Al-Ko Trailer Tongue failure

[Dave Springford]

On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:

http://www.foxonecorp.com/images/20160703_154501.jpg

In the picture you can see the front hole that has been vacated by the bolt.. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.

The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.

These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.

I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.

So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.

A few dollars in bolts might save you thousands in repairs!

Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

[JS]

Glad it had a reasonably happy ending, Dave.
You mentioned RV. Do you think the distance from axle to tow ball was a factor?

Another good set of bolts to inspect are inside the trailer, holding the tongue in place. Once discovered one of the front bolts broken during a drive across the Great Basin.
Jim

[[email protected]]

Nice save, F1! I'm towing a 1992 Cobra with the round tongue so I check that for cracks fairly regularly along with the usual hub/tire checks. But I've never towed with a motorhome and I, too, wonder if that's the common factor.

There was a flurry of concern some years ago about these earlier round trailer tongues on Cobras. Has everyone else replaced theirs already, leaving me in the minority? Or did this prove to be an issue only for those towing with larger RVs where some serious leverage could be applied?

Chip Bearden
ASW 24 "JB"

[Tom Kelley #711]

On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>
> http://www.foxonecorp.com/images/20160703_154501.jpg
>
> In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
>
> The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
>
> These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
>
> I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
>
> So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
>
> A few dollars in bolts might save you thousands in repairs!
>
> Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

Just went and checked my bolts on my 2006 Cobra trailer. Mine are original and they are 10.9 grade. Pulled behind my motor home with many miles....no problems....yet...thanks for the pictures and glad it turned out safe.

Best. #711.

[Dave Springford]

I'm certain that the towing with the RV is the contributing factor in the failure. The amount of bouncing that I see in the mirrors is astonishing and this certainly puts a significant number of cycles at higher loads on the tongue, than a car, that can lead to either a fatigue or catastrophic failure.

Tom's 10.9 bolts are rated at 145,000 psi so much closer to the imperial grade 8 bolt that I used as replacements than the original 8.8 bolts that were installed in my trailer. These are close to an imperial grade 5 bolt.

So from Tom's experience, I conclude if you tow with an RV and have 8.8 bolts replace them!

[Karl Striedieck[_2_]]

My first Duo trailer showed signs of those two cross bolts working, so I drilled a 1/2" hole vertically in that area and installed a grade 8 bolt to hold everything tight. No working thereafter.

I'll so same with replacement Duo/trailer.

Piet Barber has that rig now and he might share pics?

I'll send a picture to Dave who might post it for me. (Thanks in advance Dave!)

[Dave Springford]

Here is Karl's picture showing the location of the additional bolt.

http://www.foxonecorp.com/images/trailer.jpg

[[email protected]]

Remember that "tensile strength" measures a bolt under a longitudinal load. What you are seeing in this instance is a failure under "shear load." Two entirely different situations, and one of the main reasons that aircraft bolts (AN) are not the same as "Grade 8" or the European (DIN) equivalent. High tensile strength bolts often exhibit less than desirable brittleness under shear load.

[Per Carlin]

On Friday, July 8, 2016 at 4:31:04 AM UTC+2, wrote:
> Remember that "tensile strength" measures a bolt under a longitudinal load. What you are seeing in this instance is a failure under "shear load." Two entirely different situations, and one of the main reasons that aircraft bolts (AN) are not the same as "Grade 8" or the European (DIN) equivalent. High tensile strength bolts often exhibit less than desirable brittleness under shear load.

I think Mark is close to the root cause of the failing bolts. It is not the strength of the bolts itself that makes in brake (sounds funny, I know).
In the bolt-configuration in the initial post is the function of the bolts to hold the Al-Ko tongue tight to the square bar, the friction between the tongue and the bar makes the strength.
If the friction coefficient is low (fat, grease, dirt) or bolts is not tight (loosen by vibrations, deformations etc) is the friction between the tongue/bar low and a shear stress occurs on the bolts. The bolts are not dimensioned for this and will brake by fatigue.
This is a common problem on Cobra trailers(the nose-cone / spare wheel holder), the bolts a not tighten enough from the factory and / or they vibrate loose on the road.

[Eric Greenwell[_4_]]

Per Carlin wrote on 7/8/2016 12:43 AM:
> On Friday, July 8, 2016 at 4:31:04 AM UTC+2,
> wrote:
>> Remember that "tensile strength" measures a bolt under a
>> longitudinal load. What you are seeing in this instance is a
>> failure under "shear load." Two entirely different situations, and
>> one of the main reasons that aircraft bolts (AN) are not the same
>> as "Grade 8" or the European (DIN) equivalent. High tensile
>> strength bolts often exhibit less than desirable brittleness under
>> shear load.
>
> I think Mark is close to the root cause of the failing bolts. It is
> not the strength of the bolts itself that makes in brake (sounds
> funny, I know). In the bolt-configuration in the initial post is the
> function of the bolts to hold the Al-Ko tongue tight to the square
> bar, the friction between the tongue and the bar makes the strength.
> If the friction coefficient is low (fat, grease, dirt) or bolts is
> not tight (loosen by vibrations, deformations etc) is the friction
> between the tongue/bar low and a shear stress occurs on the bolts.
> The bolts are not dimensioned for this and will brake by fatigue.
> This is a common problem on Cobra trailers(the nose-cone / spare
> wheel holder), the bolts a not tighten enough from the factory and /
> or they vibrate loose on the road.

Can we be certain the missing bolt broke? I would expect the bolt hole
to show noticeable elongation or other damage from shearing the bolt,
especially on the side opposite the break (it would stay in the hole for
while, taking all the pounding, until that side also sheared, or the
bolt simply fell out), but the hole looks undamaged in the photo. Can't
see the other hole, however.

There is vertical bolt in the picture (about where Karl's seems to be),
just ahead of the missing bolt: what is it's function?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[[email protected]]

On Friday, July 8, 2016 at 2:43:03 AM UTC-5, Per Carlin wrote:
> On Friday, July 8, 2016 at 4:31:04 AM UTC+2, wrote:
> > Remember that "tensile strength" measures a bolt under a longitudinal load. What you are seeing in this instance is a failure under "shear load." Two entirely different situations, and one of the main reasons that aircraft bolts (AN) are not the same as "Grade 8" or the European (DIN) equivalent.. High tensile strength bolts often exhibit less than desirable brittleness under shear load.
>
> I think Mark is close to the root cause of the failing bolts. It is not the strength of the bolts itself that makes in brake (sounds funny, I know).
> In the bolt-configuration in the initial post is the function of the bolts to hold the Al-Ko tongue tight to the square bar, the friction between the tongue and the bar makes the strength.
> If the friction coefficient is low (fat, grease, dirt) or bolts is not tight (loosen by vibrations, deformations etc) is the friction between the tongue/bar low and a shear stress occurs on the bolts. The bolts are not dimensioned for this and will brake by fatigue.
> This is a common problem on Cobra trailers(the nose-cone / spare wheel holder), the bolts a not tighten enough from the factory and / or they vibrate loose on the road.

Per is right, a properly engineered bolted connection is never meant to hold shear loads. The longitudinal tension in the bolted connection should press the pieces together with a force that causes friction sufficient to withstand the bending moment.

[[email protected]]

I've often thought that the source of many trailer failures here in the U.S.. is partly that we just drive a lot more miles/kms than the typical European customer. I just got back from a nearly 5,000 mi. round trip to Nephi. And I've made numerous trips west with this trailer. How common is that in Europe?

The nose cone/spare tire holder on my Cobra failed last year and fell over (fortunately without damage) not because of a failed or loose bolt but because of a failure of the weld at the base of the supporting post. I had a failure many years ago of an Al-Ko tongue on a Komet trailer when the welds that secure the front tongue bracket inside the trailer broke.

Cobra/Komet designs have continued to improve each year since we first saw their appearance here (in the 70s?). But it seems like many of those improvements are in response to "destruction testing" performed by helpful U.S. owners. :) Is our experience shared by owners in similarly wide-open regions such as, say, Australia?

Chip Bearden
ASW 24 "JB"

[Dave Springford]

In response to Eric's comments about whether or not the bolt broke, I can not say for sure, but the bolts are secured with ny-lock nuts that should prevent an inadvertent loosening of the nut.

The vertical bolt in the picture attaches to a plate on the bottom side of the upper (inverted) U-shaped piece of the tongue. This plate then butts up against the edge of the square tube that forms the inner piece of the tongue and it appears to be there to prevent the two pieces of the tongue from moving fore and aft against each other, or perhaps for alignment during installation.

[Eric Greenwell[_4_]]

wrote on 7/8/2016 7:36 AM:
> Per is right, a properly engineered bolted connection is never meant
> to hold shear loads. The longitudinal tension in the bolted
> connection should press the pieces together with a force that causes
> friction sufficient to withstand the bending moment.

Bolts are routinely used in shear, from toys to airliners. On my glider,
the tail wheel, landing gear, and propeller are fastened with bolts in
shear, along with many other items.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[[email protected]]

On Friday, July 8, 2016 at 10:26:09 AM UTC-5, Eric Greenwell wrote:
> wrote on 7/8/2016 7:36 AM:
> > Per is right, a properly engineered bolted connection is never meant
> > to hold shear loads. The longitudinal tension in the bolted
> > connection should press the pieces together with a force that causes
> > friction sufficient to withstand the bending moment.
>
> Bolts are routinely used in shear, from toys to airliners. On my glider,
> the tail wheel, landing gear, and propeller are fastened with bolts in
> shear, along with many other items.
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> email me)
> - "A Guide to Self-Launching Sailplane Operation"
>
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> - "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm
>
> http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

Sorry Eric, you are wrong. Pretension (torque) on the bolt results in parts being pressed together. That force with a coefficient of friction normally being assumed at 0.1 results in the parts staying together without slippage. Shear can only occur if the parts slip, a properly designed connection never does.

[Craig Funston]

On Friday, July 8, 2016 at 9:05:24 AM UTC-7, wrote:
> On Friday, July 8, 2016 at 10:26:09 AM UTC-5, Eric Greenwell wrote:
> > wrote on 7/8/2016 7:36 AM:
> > > Per is right, a properly engineered bolted connection is never meant
> > > to hold shear loads. The longitudinal tension in the bolted
> > > connection should press the pieces together with a force that causes
> > > friction sufficient to withstand the bending moment.
> >
> > Bolts are routinely used in shear, from toys to airliners. On my glider,
> > the tail wheel, landing gear, and propeller are fastened with bolts in
> > shear, along with many other items.
> >
> > --
> > Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> > email me)
> > - "A Guide to Self-Launching Sailplane Operation"
> >
> > https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> > - "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm
> >
> > http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf
>
> Sorry Eric, you are wrong. Pretension (torque) on the bolt results in parts being pressed together. That force with a coefficient of friction normally being assumed at 0.1 results in the parts staying together without slippage. Shear can only occur if the parts slip, a properly designed connection never does.

Herb,

There are some cases where friction is what is relied on for a bolted shear connection, but these are very special cases and require specific installation procedures. In building structures, these bolts are designated ASTM A325 SC or ASTM A490 SC. The "SC" designating slip critical. In order to perform as slip critical connections there needs to be enough capacity in the bolted sandwich to allow the bolt to yield slightly in tension during tightening. This provides a consistent preload to develop the friction. This type of connection is impossible to achieve when bolting though a hollow tube unless there is a bearing sleeve through the tube to allow development of full tension in the bolt. Without the bearing sleeve the bolt simply crushes the tube and sufficient clamping force is never achieved. Many buildings and other structures are designed and constructed using bolts in shear without relying on friction between the faying surfaces. Slip critical bolting (friction bolting) is a nice solution when cyclic loads and fatigue are a consideration because it eliminates the movement that happens when bearing bolts (bolts in plain shear) are cycled from one load direction to another. Cyclic loading can also be accommodated by interference fit bolts, but the degree of accuracy required in fabrication is too expensive for all but specialty applications.

Best regards,
Craig Funston, P.E. , S.E. , P.Eng.

[Craig Funston]

On Thursday, July 7, 2016 at 2:21:21 PM UTC-7, Dave Springford wrote:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>
> http://www.foxonecorp.com/images/20160703_154501.jpg
>
> In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
>
> The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
>
> These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
>
> I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
>
> So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
>
> A few dollars in bolts might save you thousands in repairs!
>
> Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

Dave,

Did the vertical bolt ahead of the horizontal ones fail as well or did the nut come off the bottom? That's usually the primary load path for the vertical prying loads introduced by coupling the hitch assembly with the drawbar.

[Craig Funston]

On Friday, July 8, 2016 at 7:55:50 AM UTC-7, Dave Springford wrote:
> In response to Eric's comments about whether or not the bolt broke, I can not say for sure, but the bolts are secured with ny-lock nuts that should prevent an inadvertent loosening of the nut.
>
> The vertical bolt in the picture attaches to a plate on the bottom side of the upper (inverted) U-shaped piece of the tongue. This plate then butts up against the edge of the square tube that forms the inner piece of the tongue and it appears to be there to prevent the two pieces of the tongue from moving fore and aft against each other, or perhaps for alignment during installation.

Dave,

Just saw your comment on the vertical bolt. Please ignore my prior note.
Craig

[[email protected]]

Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.

On Thursday, July 7, 2016 at 5:21:21 PM UTC-4, Dave Springford wrote:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>

[Casey[_2_]]

On Friday, July 8, 2016 at 4:08:38 PM UTC-4, wrote:
> Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.

Right On. I can't believe they are still using steel wheels with hub caps. Nice aluminum rims are not even an option. Not sure if current hubs come with bearing buddy/quick lube fittings. But if not that is amazing as well.. A shot of synthetic grease every couple of years and one would never need to replace bearings or have to open bearing cap.

[Craig Funston]

On Friday, July 8, 2016 at 1:08:38 PM UTC-7, wrote:
> Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.
>
> On Thursday, July 7, 2016 at 5:21:21 PM UTC-4, Dave Springford wrote:
> > On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
> >

No intention to get off into the weeds on bolting technology, but there's no evidence at this point indicating a bolt shear failure rather than the bolt working its way out. Dave would have likely found the remainder of the bolt shank in the square section draw bar if the bolt failed in shear. If there was nothing remaining then the probable scenario is the nut coming loose and the bolt working its way out. Dave will have to let us know what the situation really was. If the nut came loose then loctite is a better solution than nylocks and there's no need to upgrade the bolts on your new trailer.

[JS]

On Friday, July 8, 2016 at 2:13:45 PM UTC-7, Casey wrote:
> On Friday, July 8, 2016 at 4:08:38 PM UTC-4, wrote:
> > Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.
>
> Right On. I can't believe they are still using steel wheels with hub caps. Nice aluminum rims are not even an option. Not sure if current hubs come with bearing buddy/quick lube fittings. But if not that is amazing as well. A shot of synthetic grease every couple of years and one would never need to replace bearings or have to open bearing cap.

Has anyone checked if their fuel tank is within the range of motion the chains will allow?

To get an idea of what the trailer tongue has to deal with behind an RV, try riding in the back seat of one of those shuttle buses built on a truck chassis, AKA "short bus". Enjoy a glass of something colorful if you dare. After that, the idea of loosening or breaking things shouldn't come as a big surprise.

Casey, you've probably noticed when replacing the steel wheels on your own trailer that AlKo have used sealed bearings for more than a decade.

Jim

[Charlie M. (UH & 002 owner/pilot)]

Keep in mind (not really directed to Herb....) if you upgrade the bolt rating, it ALSO requires a higher torque value to maintain the correct clamping force within the elastic limits of the fastener.
Common issue is, "well hey, I put in better hardware, but it still failed!!", person never properly torqued the better hardware to an appropriate torque valve within elastic range.
I'll stay out of lubed vs. dry threads, rusty vs. clean threads........

[[email protected]]

Just checked my trailer year 2011 and the same cross bolt was sheared at the nut. The bolt was still in but the nut was gone and you could see the shear plane. and yes the trailer is towed with a motor home.

David
ASG29E BV

[Eric Greenwell[_4_]]

wrote on 7/8/2016 7:20 PM:
> Just checked my trailer year 2011 and the same cross bolt was sheared
> at the nut. The bolt was still in but the nut was gone and you could
> see the shear plane. and yes the trailer is towed with a motor
> home.

Were there any threads on the bolt in the sheared area?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Casey[_2_]]

On Friday, July 8, 2016 at 6:14:51 PM UTC-4, JS wrote:
> On Friday, July 8, 2016 at 2:13:45 PM UTC-7, Casey wrote:
> > On Friday, July 8, 2016 at 4:08:38 PM UTC-4, wrote:
> > > Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.
> >
> > Right On. I can't believe they are still using steel wheels with hub caps. Nice aluminum rims are not even an option. Not sure if current hubs come with bearing buddy/quick lube fittings. But if not that is amazing as well. A shot of synthetic grease every couple of years and one would never need to replace bearings or have to open bearing cap.
>
> Has anyone checked if their fuel tank is within the range of motion the chains will allow?
>
> To get an idea of what the trailer tongue has to deal with behind an RV, try riding in the back seat of one of those shuttle buses built on a truck chassis, AKA "short bus". Enjoy a glass of something colorful if you dare. After that, the idea of loosening or breaking things shouldn't come as a big surprise.
>
> Casey, you've probably noticed when replacing the steel wheels on your own trailer that AlKo have used sealed bearings for more than a decade.
>
> Jim

Jim,
Wow. I did not realize that. My trailer is a 1975 Pfeiffer but probably does have the Alko axle. The bearings are not sealed of course. I pulled the bearings out, inspected, cleaned and re-greased with synthetic grease. I'm so use to re-greasing trailer bearings that I did not even know/realize that they were using sealed bearings. I never had a trailer with sealed bearings. I guess not common in the US. I just wonder why they are still using steel wheels and hub caps without a upgrade to aluminum wheels.

Casey

[[email protected]]

In answer to the question if the bolt was sheared in the thread plane. Yes.. It looks to me like the threads were crushed in the original shear plane with the bolt tight and that allowed the nut to come loose and back off a bit. The actual shear was about 1/2" from the end of the bolt. There is about 3/4" of thread remaining. Ideally the shear plane should not have threads.

David
ASG29E BV

[Karl Striedieck[_2_]]

Here's a better picture of the bolt I added to the tongue of the Duo trailer to eliminate the shear loads on the two cross bolts.

http://www.foxonecorp.com/images/tongue%20bolt.jpg

KS

[Ramy[_2_]]

On the subject of trailer tongue issues, I just noticed that the coupler can rotate 360 degrees inside the tongue round tube in my Cobra trailer. It was always relatively loose and could rotate 30 degrees but not 360. Not sure when it happened but it towed just fine before I noticed this today. Nothing looks broken and all bolts seem to be in place. Problem is that I am in the middle of a flying trip. Anyone experienced this or has an idea what is going on and how to fix this? And most importantly, is the trailer still road worthy?

Thanks

Ramy

[Ramy[_2_]]

Got a very quick reply from Alfred that my issue is simple to fix and not a big concern so I am relieved. Excellent customer service.

Ramy

[[email protected]]

To answer Ramy's question, I have had two trailers who's hitch would rotate 360 degrees......... Never any problem. It can't rotate off the ball and is limited to about 30 degrees by the hitch sides.
Now, I'd like to ask (and answer) why these hitch bolts are failing. AN bolts are good for 125,000 psi, but these are common hardware bolts, so let's say they are good for 100,000 psi tensil strength. A half inch bolt cross section would have .19635 area X 100,000 = 19,635 t/s. Say 50% for shear strength, no let's say 40% because the shear load in on the threads = 7854 psi shear strength...........we can expect the bolt to shear off when 7854 pounds of force is applied.
Now, let's take a look at what's happening as we exit a gas station in out motor home with a large over-hang.........tow ball 10 feet behing the rear axle. As the rear wheels approach the curb (low point at edge of road) the rear end of our motor home drops and the trailer tung skid starts dragging across the pavement, but the motor home rear wheels are not yet all the way down to the curb. At this point the a good portion of the weight of the MH is pulling down on the tow ball. Our trailer skid is now acting as a sliding fulcrum and trying to lift the trailer. Most MH weigh a good 10,000 pounds, so let's say half of that is pulling down on the tow ball.
The bolts that have sheared off are located 15" behind the skid plate and the ball is about 10" forward of the skid, so we have a one to one and a half ratio. 5000# X 1.5 ratio = 7500# shear force applied to our half inch bolt that should shear off at 7850#.
I'm sure the engineering types in this group will have fun pointing out the errors in my thought process.
;>) JJ

[Dan Marotta]

So... What was the fix?


On 7/9/2016 11:12 PM, Ramy wrote:
> Got a very quick reply from Alfred that my issue is simple to fix and not a big concern so I am relieved. Excellent customer service.
>
> Ramy

--
Dan, 5J

[jfitch]

On Sunday, July 10, 2016 at 1:20:11 AM UTC-7, wrote:
> To answer Ramy's question, I have had two trailers who's hitch would rotate 360 degrees......... Never any problem. It can't rotate off the ball and is limited to about 30 degrees by the hitch sides.
> Now, I'd like to ask (and answer) why these hitch bolts are failing. AN bolts are good for 125,000 psi, but these are common hardware bolts, so let's say they are good for 100,000 psi tensil strength. A half inch bolt cross section would have .19635 area X 100,000 = 19,635 t/s. Say 50% for shear strength, no let's say 40% because the shear load in on the threads = 7854 psi shear strength...........we can expect the bolt to shear off when 7854 pounds of force is applied.
> Now, let's take a look at what's happening as we exit a gas station in out motor home with a large over-hang.........tow ball 10 feet behing the rear axle. As the rear wheels approach the curb (low point at edge of road) the rear end of our motor home drops and the trailer tung skid starts dragging across the pavement, but the motor home rear wheels are not yet all the way down to the curb. At this point the a good portion of the weight of the MH is pulling down on the tow ball. Our trailer skid is now acting as a sliding fulcrum and trying to lift the trailer. Most MH weigh a good 10,000 pounds, so let's say half of that is pulling down on the tow ball.
> The bolts that have sheared off are located 15" behind the skid plate and the ball is about 10" forward of the skid, so we have a one to one and a half ratio. 5000# X 1.5 ratio = 7500# shear force applied to our half inch bolt that should shear off at 7850#.
> I'm sure the engineering types in this group will have fun pointing out the errors in my thought process.
> ;>) JJ

Well, one thing is that the bolts are in double shear and so should be good for twice that.

I'd go more with the fatigue argument. With a large overhang, sometimes the trailer gets into some serious pitch oscillations with large reversing stresses. Not amenable to simple analysis.

Trust me, I'm an engineer:
https://youtu.be/rp8hvyjZWHs

[[email protected]]

Fix? Best to roll down drivers window and listen for any scraping noise as you exit any parking area. Stop immediately if trailer skid makes contact. Probably best way to proceed is un-hook trailer and move it by hand past the curb problem area.
JJ

[Ramy[_2_]]

To fix the rotating issue I mentioned (not the main issue in this thread) I will need to order a little sliding part to replace the damaged one.

Ramy

[[email protected]]

Interesting analysis jj, mine failed on a new tongue hitch, I lost the vertical bolt and part of the hitch plate but it was because the tail end of the trailer drags occasionally when entering or departing deep curbs at entrances. Putting the entire weight of the trailer on the younger at the ball and the back skids of the trailer. The best way I see to reduce this chance is whenever possible go across the depressions at at relatively low angle of 45 degrees or less if possible so only one wheel of motorhome and or trailer goes in the depression at a time. Traffic can make this a chore at times but it works.

[Dan Marotta]

Thanks Ramy. ...And JJ's solution is the most elegant!


On 7/10/2016 9:42 AM, Ramy wrote:
> To fix the rotating issue I mentioned (not the main issue in this thread) I will need to order a little sliding part to replace the damaged one.
>
> Ramy

--
Dan, 5J

[[email protected]]

If you have frequent issues with dragging, consider shimming your trailer axle with a 1" or 2" tube.

[JS]

On Sunday, July 10, 2016 at 8:43:34 AM UTC-7, wrote:
> Interesting analysis jj, mine failed on a new tongue hitch, I lost the vertical bolt and part of the hitch plate but it was because the tail end of the trailer drags occasionally when entering or departing deep curbs at entrances. Putting the entire weight of the trailer on the younger at the ball and the back skids of the trailer. The best way I see to reduce this chance is whenever possible go across the depressions at at relatively low angle of 45 degrees or less if possible so only one wheel of motorhome and or trailer goes in the depression at a time. Traffic can make this a chore at times but it works.

Some people react to the tail dragging by using a drop coupler on the tow vehicle. This puts the tongue of the trailer in a lower and more vulnerable position, the condition JJ warns of.
The trailer should be level. You should be able to rig the glider with the trailer hooked to the vehicle.

Spindelberger sells lift kits in a couple of heights. They are pretty inexpensive, and easily installed between the body of the trailer and the axle.
Here's a photo of one on an ASH26E trailer which had 13" wheels. The 26 trailer is long and this one was too low.

https://www.dropbox.com/s/37wtbsd4cs6xkyo/Cobra%20Trailer%20Lift%20Kit.jpg?dl=0

Spindelberger would normally have parts galvanized, but made my part to order and needed to put together a larger batch. As I wanted it right away, it ended up painted.
Jim

[[email protected]]

On Sunday, July 10, 2016 at 12:19:29 PM UTC-4, wrote:
> If you have frequent issues with dragging, consider shimming your trailer axle with a 1" or 2" tube.

A size large (diameter) tires does the same. 1/2" at the axle gives about twice that much more clearance at the aft end of the trailer.

Of course, if you rig while the trailer is hitched to the tow vehicle, that changes the angle of departure when you're pulling the fuselage out (watch out for scrapes) and forces you to lift the spars off the dollies from a higher position. Nothing is free in this world. :)

Chip Bearden
ASW 24 "JB"

[lynn]

On Friday, July 8, 2016 at 9:29:13 AM UTC-7, Craig Funston wrote:
> On Friday, July 8, 2016 at 9:05:24 AM UTC-7, wrote:
> > On Friday, July 8, 2016 at 10:26:09 AM UTC-5, Eric Greenwell wrote:
> > > wrote on 7/8/2016 7:36 AM:
> > > > Per is right, a properly engineered bolted connection is never meant
> > > > to hold shear loads. The longitudinal tension in the bolted
> > > > connection should press the pieces together with a force that causes
> > > > friction sufficient to withstand the bending moment.
> > >
> > > Bolts are routinely used in shear, from toys to airliners. On my glider,
> > > the tail wheel, landing gear, and propeller are fastened with bolts in
> > > shear, along with many other items.
> > >
> > > --
> > > Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> > > email me)
> > > - "A Guide to Self-Launching Sailplane Operation"
> > >
> > > https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> > > - "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm
> > >
> > > http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf
> >
> > Sorry Eric, you are wrong. Pretension (torque) on the bolt results in parts being pressed together. That force with a coefficient of friction normally being assumed at 0.1 results in the parts staying together without slippage. Shear can only occur if the parts slip, a properly designed connection never does.
>
> Herb,
>
> There are some cases where friction is what is relied on for a bolted shear connection, but these are very special cases and require specific installation procedures. In building structures, these bolts are designated ASTM A325 SC or ASTM A490 SC. The "SC" designating slip critical. In order to perform as slip critical connections there needs to be enough capacity in the bolted sandwich to allow the bolt to yield slightly in tension during tightening. This provides a consistent preload to develop the friction. This type of connection is impossible to achieve when bolting though a hollow tube unless there is a bearing sleeve through the tube to allow development of full tension in the bolt. Without the bearing sleeve the bolt simply crushes the tube and sufficient clamping force is never achieved. Many buildings and other structures are designed and constructed using bolts in shear without relying on friction between the faying surfaces. Slip critical bolting (friction bolting) is a nice solution when cyclic loads and fatigue are a consideration because it eliminates the movement that happens when bearing bolts (bolts in plain shear) are cycled from one load direction to another. Cyclic loading can also be accommodated by interference fit bolts, but the degree of accuracy required in fabrication is too expensive for all but specialty applications.
>
> Best regards,
> Craig Funston, P.E. , S.E. , P.Eng.

I was about to start in with the shear versus friction discussion on bolted joints when I saw Craig's discussion. He is absolutely correct. I have been in the crane design industry for many decades and use the friction joint technique when using many bolts in a connection but when one bolt is used, shear is usually the design mode. Lynn Wyman, P.E.

[Auxvache]

Thanks F1 and company--love the shared knowledge here.

I've had one nose cone bolt and one front handle/top bolt fail, and carry all spares. Just back from Utah, and I'm again amazed and dismayed at some of our roads in the U.S. The road-bridge-road junction must be very hard to engineer--ugh.

Anyone successfully upgrade the Cobra suspension to help with the sharp jar and also big dips? I run 13" trailer tires at high psi, original steel rims. Does Cobra offer a heavy duty option for insert-state-here?

Thanks in advance.

[2G]

On Monday, July 11, 2016 at 1:43:56 PM UTC-7, Auxvache wrote:
> Thanks F1 and company--love the shared knowledge here.
>
> I've had one nose cone bolt and one front handle/top bolt fail, and carry all spares. Just back from Utah, and I'm again amazed and dismayed at some of our roads in the U.S. The road-bridge-road junction must be very hard to engineer--ugh.
>
> Anyone successfully upgrade the Cobra suspension to help with the sharp jar and also big dips? I run 13" trailer tires at high psi, original steel rims. Does Cobra offer a heavy duty option for insert-state-here?
>
> Thanks in advance.

That bolt did not fail because it was under-specified for the application - there is something else going on here. Adding a bolt with greater strength will not resolve the issue. Just think about it: what forces are being applied to the bolt by towing that would have caused it to fail? As an engineer, I have seen so many times when people become fixated on the wrong cause of the problem (I have done it myself). You may have just have had a nut that came loose because of vibration.

Tom

[Dave Springford]

Hi Tom,

Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).

After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.

I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.

[AS]

On Monday, July 11, 2016 at 4:43:56 PM UTC-4, Auxvache wrote:
Just back from Utah, and I'm again amazed and dismayed at some of our roads in the U.S. The road-bridge-road junction must be very hard to engineer--ugh.
>

I can only second that, 'At the cows'! I just returned from Moriarty on I-40. West Memphis has a long bridge or elevated highway build with concrete sections which are all sagging in the middle. That excited my van and two-axle trailer to the point where I felt the front wheels coming off the ground.. The whole rig was galloping and the only way to make it stop was to slow down to about 35mph, which did not please the truckers behind me. I did inspect the Cobra trailer, ALKO tow bar assembly and the contents of the trailer afterwards and did still find everything being tight and in place.
Road/Highway maintenance does not seem to be important in certain states.

Uli
AS

[Dan Marotta]

A question for the mechanical engineers on this group:

Isn't it true that the load rating of a bolt is an indication of the
tensile strength of the bolt and not its shear strength? Is there any
indication of the shear strength of a bolt? Can anything be inferred
about shear strength from tensile strength?

On 7/20/2016 8:31 PM, Dave Springford wrote:
> Hi Tom,
>
> Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
>
> After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
>
> I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
>

--
Dan, 5J

[AS]

On Thursday, July 21, 2016 at 10:43:44 AM UTC-4, Dan Marotta wrote:
> A question for the mechanical engineers on this group:
>
> Isn't it true that the load rating of a bolt is an indication of the
> tensile strength of the bolt and not its shear strength? Is there any
> indication of the shear strength of a bolt? Can anything be inferred
> about shear strength from tensile strength?
>
> On 7/20/2016 8:31 PM, Dave Springford wrote:
> > Hi Tom,
> >
> > Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
> >
> > After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
> >
> > I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
> >
>
> --
> Dan, 5J

Dan - bolting theory 101: Never design a bolted joint where the bolt(s) are going into shear! A bolt is supposed to clamp two or more members together and the whole thing is supposed to hold together by friction. If the joint moves, the axial pre-stress or clamping force provided by the bolt(s) was not high enough! Short, stubby bolts will not hold their clamping force for long. That's why long, slender bolts that can be elongated up to their yield point and act as axial springs are preferred over short, stubby ones. Going up in bolt diameter does in most cases not solve the problem.
If you really want to improve the ALKO design, use stand-off bushings (NOT stacks of washers!) and longer bolts. Figure out what the torque rating for that bolt grade is and precisely torque it to that value. Use a good torque wrench and NOT Bubba on a 3ft cheater pipe!

Uli
AS

[Craig Funston]

On Thursday, July 21, 2016 at 7:43:44 AM UTC-7, Dan Marotta wrote:
> A question for the mechanical engineers on this group:
>
> Isn't it true that the load rating of a bolt is an indication of the
> tensile strength of the bolt and not its shear strength? Is there any
> indication of the shear strength of a bolt? Can anything be inferred
> about shear strength from tensile strength?
>
> On 7/20/2016 8:31 PM, Dave Springford wrote:
> > Hi Tom,
> >
> > Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
> >
> > After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
> >
> > I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
> >
>
> --
> Dan, 5J

For typical steels used in bolt fabrication, shear strength correlates pretty well with tensile strength. Current guidance from the American Institute of Steel Construction use a shear strength equal to 60% of the tensile strength (ultimate values, not yield). This is for a bearing type (not friction) connection with threads included in the shear plane. High strength bolts are allowed shears up to 75% of tensile if the threads are excluded from the shear plane.

Craig
7Q

[Craig Funston]

On Thursday, July 21, 2016 at 9:12:54 AM UTC-7, AS wrote:
> On Thursday, July 21, 2016 at 10:43:44 AM UTC-4, Dan Marotta wrote:
> > A question for the mechanical engineers on this group:
> >
> > Isn't it true that the load rating of a bolt is an indication of the
> > tensile strength of the bolt and not its shear strength? Is there any
> > indication of the shear strength of a bolt? Can anything be inferred
> > about shear strength from tensile strength?
> >
> > On 7/20/2016 8:31 PM, Dave Springford wrote:
> > > Hi Tom,
> > >
> > > Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
> > >
> > > After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
> > >
> > > I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
> > >
> >
> > --
> > Dan, 5J
>
> Dan - bolting theory 101: Never design a bolted joint where the bolt(s) are going into shear! A bolt is supposed to clamp two or more members together and the whole thing is supposed to hold together by friction. If the joint moves, the axial pre-stress or clamping force provided by the bolt(s) was not high enough! Short, stubby bolts will not hold their clamping force for long. That's why long, slender bolts that can be elongated up to their yield point and act as axial springs are preferred over short, stubby ones. Going up in bolt diameter does in most cases not solve the problem.
> If you really want to improve the ALKO design, use stand-off bushings (NOT stacks of washers!) and longer bolts. Figure out what the torque rating for that bolt grade is and precisely torque it to that value. Use a good torque wrench and NOT Bubba on a 3ft cheater pipe!
>
> Uli
> AS

Uli,

Use of bearing vs. friction for bolts in shear depends on which industry you're operating in. For building structures it's quite common to use bolts in bearing since often the loads are relatively static. Friction bolting is advantageous in applications where the loads are cyclic and fatigue is a concern. It's also advantageous for applications that require accommodation of loose field tolerances since the bolts can be tightened to clamping friction and the bolt holes can be oversize or slotted.

I agree the ALKO tongue connection is subject to cyclic loads and fatigue and would benefit from a properly installed friction bolted connection. A compression bushing between the inside walls of the square tube is needed to develop the proper clamping force. Drilling a larger hole for a bushing and pushing it through the square tube won't accomplish the goal.

Craig
7Q

[Dan Marotta]

Very informative, thanks!

How about this for the use in question: Drill the holes in the trailer
tongue oversize and use a steel bushing the exact length of the outer
tube of the tongue. Then use a high strength bolt to hold it together.
Or simply a trailer hitch pin with a spring clip or lock to hold it in
place.

On 7/21/2016 10:23 AM, Craig Funston wrote:
> On Thursday, July 21, 2016 at 7:43:44 AM UTC-7, Dan Marotta wrote:
>> A question for the mechanical engineers on this group:
>>
>> Isn't it true that the load rating of a bolt is an indication of the
>> tensile strength of the bolt and not its shear strength? Is there any
>> indication of the shear strength of a bolt? Can anything be inferred
>> about shear strength from tensile strength?
>>
>> On 7/20/2016 8:31 PM, Dave Springford wrote:
>>> Hi Tom,
>>>
>>> Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
>>>
>>> After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
>>>
>>> I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
>>>
>> --
>> Dan, 5J
> For typical steels used in bolt fabrication, shear strength correlates pretty well with tensile strength. Current guidance from the American Institute of Steel Construction use a shear strength equal to 60% of the tensile strength (ultimate values, not yield). This is for a bearing type (not friction) connection with threads included in the shear plane. High strength bolts are allowed shears up to 75% of tensile if the threads are excluded from the shear plane.
>
> Craig
> 7Q

--
Dan, 5J

[Craig Funston]

On Thursday, July 21, 2016 at 9:45:47 AM UTC-7, Dan Marotta wrote:
> Very informative, thanks!
>
> How about this for the use in question: Drill the holes in the trailer
> tongue oversize and use a steel bushing the exact length of the outer
> tube of the tongue. Then use a high strength bolt to hold it together.
> Or simply a trailer hitch pin with a spring clip or lock to hold it in
> place.
>
> On 7/21/2016 10:23 AM, Craig Funston wrote:
> > On Thursday, July 21, 2016 at 7:43:44 AM UTC-7, Dan Marotta wrote:
> >> A question for the mechanical engineers on this group:
> >>
> >> Isn't it true that the load rating of a bolt is an indication of the
> >> tensile strength of the bolt and not its shear strength? Is there any
> >> indication of the shear strength of a bolt? Can anything be inferred
> >> about shear strength from tensile strength?
> >>
> >> On 7/20/2016 8:31 PM, Dave Springford wrote:
> >>> Hi Tom,
> >>>
> >>> Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
> >>>
> >>> After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
> >>>
> >>> I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
> >>>
> >> --
> >> Dan, 5J
> > For typical steels used in bolt fabrication, shear strength correlates pretty well with tensile strength. Current guidance from the American Institute of Steel Construction use a shear strength equal to 60% of the tensile strength (ultimate values, not yield). This is for a bearing type (not friction) connection with threads included in the shear plane. High strength bolts are allowed shears up to 75% of tensile if the threads are excluded from the shear plane.
> >
> > Craig
> > 7Q
>
> --
> Dan, 5J

Drilling oversize holes in the tongue for a bushing just makes the bushing the bearing member and takes away any possibility of developing clamping force on the tongue which is where it's needed.

The bushing could be welded into the tongue or shorter bushings that are fed in from the end of the square tube to brace the sidewalls against compression from the bolt could be used

Craig

[Charlie M. (UH & 002 owner/pilot)]

Not so good, better would be a "reverse fishmouth" on a steel bushing that fit INSIDE the inner tube and aligned with the bolt hole. Then, properly torque the bolt (depends on grade, diameter and length) so the bolt loads a "solid structure".
Currently, the design allows for some "crush" of the tongue thus losing some of the clamping force. Threads in shear are also not a good thing for strength, but may be fine for "torque limiting" as in a snowblower auger.

Note: you could also use a length of bar stock inside the inner tube rather than my first thought.

[Charlie M. (UH & 002 owner/pilot)]

Another note, I was describing a fix for the round tube tongue, square tube would be similar. Another thought, whatever "internal spacer" you get should have a larger diameter/size than the area under the nut or bolt head, NOT a thin tube.

[[email protected]]

On Wednesday, July 20, 2016 at 10:31:52 PM UTC-4, Dave Springford wrote:
> Hi Tom,
>
> Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
>
> After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
>
> I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.

Rather than put a lot of time into the bolt specification, why not "simply" drill the holes out to 5/8" and get 50% more strength?
I'm going to look at doing that on mine.
UH

[AS]

> Uli,
>
> Use of bearing vs. friction for bolts in shear depends on which industry you're operating in. For building structures it's quite common to use bolts in bearing since often the loads are relatively static. Friction bolting is advantageous in applications where the loads are cyclic and fatigue is a concern. It's also advantageous for applications that require accommodation of loose field tolerances since the bolts can be tightened to clamping friction and the bolt holes can be oversize or slotted.
>
> I agree the ALKO tongue connection is subject to cyclic loads and fatigue and would benefit from a properly installed friction bolted connection. A compression bushing between the inside walls of the square tube is needed to develop the proper clamping force. Drilling a larger hole for a bushing and pushing it through the square tube won't accomplish the goal.
>
> Craig
> 7Q

Hi Craig - point taken! I didn't even think about static applications. I designed mining and tunneling machines and now I engineer around wind turbines. Think high vibrations and dynamics in both cases, so in my world, stuff is constantly trying to fall apart while I desperately try to keep it together - with bolts as long and tightly torqued as the materials allow ;-)

Uli
AS

[Ian[_2_]]

On 21/07/2016 18:35, Craig Funston wrote:
> Use of bearing vs. friction for bolts in shear depends on which
> industry you're operating in. For building structures it's quite
> common to use bolts in bearing since often the loads are relatively
> static. Friction bolting is advantageous in applications where the
> loads are cyclic and fatigue is a concern. It's also advantageous
> for applications that require accommodation of loose field
> tolerances since the bolts can be tightened to clamping friction and
> the bolt holes can be oversize or slotted.

> I agree the ALKO tongue connection is subject to cyclic loads and
> fatigue and would benefit from a properly installed friction bolted
> connection. A compression bushing between the inside walls of the
> square tube is needed to develop the proper clamping force.
> Drilling a larger hole for a bushing and pushing it through the
> square tube won't accomplish the goal.


From my understanding of bolted joints, cyclic shear loads can induce
fatigue failure and using a higher strength steel is not going to
prevent fatigue. I suspect the designers underestimated the number and
magnitude of the fatigue cycles these trailers are subject to when towed
behind motor homes.

Note I have not looked at one of these in person to know if these
suggestions are practical. But I would look for a simpler fix:

- Drill out the 12mm bolts and fit 16mm bolts, and make the problem "go
away" for a long time, hopefully forever.

or

- Drill additional holes for 2 extra 12 mm bolts, one adjacent to each
of the existing ones. Then fit two extra bolts, but with one head of
each pair of bolts on opposite sides of the trailer. Biggest advantage
of this is there are now four bolts and any 3 will easily carry the
load. So if you check it once in a while and find a bolt missing or
damaged, you will have ample chance to replace it and check the other 3,
before things deteriorate to a point of potential catastrophic failure.

In reality the redundant bolts will probably not take any load, but
hopefully with pairs of bolts fitted from opposing sides, their will be
an un-threaded portion bolt to take the load in each major shear plane.

Ian

[Nigel Pocock[_2_]]

As an ignorant non-engineer why not reduce the cause of the problem
rather than use a technical solution to it.
As I understand it the problem seams to be caused by excessive
pitching of the trailer exceeding the design loads on the tongue.
What caused this pitching? One thing mentioned it is large overhangs
between the rear axle and the hitch on the tow vehicle. If this is
sufficient to cause problems with the integrity of the tongue what is it
doing to the glider inside?
Another problem is loading the trailer so there is too much weight on
the tongue. The pitching causes a loading + or _ around that weight.
i.e if the tongue weight is 30lb and pitching causes a variation of +or -
100lb the load would vary between -70 and +130. If the tongue weight
was 100lb plus as I have seen recommended on this site it would vary
between 0 and 200lb. Insert your own figures but you get the gist of
my argument.
As a matter of interest I havnt heard of this problem on this side of the
pond where we usually tow with much more compact, lighter vehicles.

[Eric Greenwell[_4_]]

Nigel Pocock wrote on 7/22/2016 8:32 AM:
> As an ignorant non-engineer why not reduce the cause of the problem
> rather than use a technical solution to it.
> As I understand it the problem seams to be caused by excessive
> pitching of the trailer exceeding the design loads on the tongue.
> What caused this pitching? One thing mentioned it is large overhangs
> between the rear axle and the hitch on the tow vehicle. If this is
> sufficient to cause problems with the integrity of the tongue what is it
> doing to the glider inside?
> Another problem is loading the trailer so there is too much weight on
> the tongue. The pitching causes a loading + or _ around that weight.
> i.e if the tongue weight is 30lb and pitching causes a variation of +or -
> 100lb the load would vary between -70 and +130. If the tongue weight
> was 100lb plus as I have seen recommended on this site it would vary
> between 0 and 200lb. Insert your own figures but you get the gist of
> my argument.
> As a matter of interest I havnt heard of this problem on this side of the
> pond where we usually tow with much more compact, lighter vehicles.

Changing to a more trailer-friendly towing vehicle than a motorhome is a
non-starter if I want my wife to travel with me; I also prefer
traveling (particularly to glider events) in a motorhome.


It does happen on your side of the pond when towing with motorhomes, but
likely isn't as common due to fewer towing miles and smaller motorhomes.
I've towed my ASH 26 E more than 170,000 miles in it's Cobra trailer,
and it's in fine shape, so the pitching doesn't seem to be a problem for
the glider. I did have to replace the original, smaller tongue about 15
years ago, which developed a crack at the weld for the tongue wheel mount.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Craig Funston]

On Thursday, July 21, 2016 at 6:42:04 PM UTC-7, AS wrote:
> > Uli,
> >
> > Use of bearing vs. friction for bolts in shear depends on which industry you're operating in. For building structures it's quite common to use bolts in bearing since often the loads are relatively static. Friction bolting is advantageous in applications where the loads are cyclic and fatigue is a concern. It's also advantageous for applications that require accommodation of loose field tolerances since the bolts can be tightened to clamping friction and the bolt holes can be oversize or slotted.
> >
> > I agree the ALKO tongue connection is subject to cyclic loads and fatigue and would benefit from a properly installed friction bolted connection. A compression bushing between the inside walls of the square tube is needed to develop the proper clamping force. Drilling a larger hole for a bushing and pushing it through the square tube won't accomplish the goal.
> >
> > Craig
> > 7Q
>
> Hi Craig - point taken! I didn't even think about static applications. I designed mining and tunneling machines and now I engineer around wind turbines. Think high vibrations and dynamics in both cases, so in my world, stuff is constantly trying to fall apart while I desperately try to keep it together - with bolts as long and tightly torqued as the materials allow ;-)
>
> Uli
> AS

Hi Uli,

I can absolutely see why clamping force is king. Lots of other things to consider as well I'm sure. I remember being fascinated by the use of tapered studs to control shear lag / bond stresses in the bonded steel fasteners for the FRP blades. Interesting industry.

Cheers,
Craig
7Q

[Piet Barber]

On Thursday, July 7, 2016 at 9:21:28 PM UTC-4, Karl Striedieck wrote:
> My first Duo trailer showed signs of those two cross bolts working, so I drilled a 1/2" hole vertically in that area and installed a grade 8 bolt to hold everything tight. No working thereafter.
>
> I'll so same with replacement Duo/trailer.
>
> Piet Barber has that rig now and he might share pics?

I took some pictures of this on Saturday, hope they help the discussion a bit:

https://sites.google.com/a/pietbarber.com/www/home/cobra-modification

[Hartley Falbaum[_2_]]

On Thursday, July 7, 2016 at 5:21:21 PM UTC-4, Dave Springford wrote:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>
> http://www.foxonecorp.com/images/20160703_154501.jpg
>
> In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
>
> The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
>
> These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
>
> I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
>
> So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
>
> A few dollars in bolts might save you thousands in repairs!
>
> Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.



Piet---check your jockey wheel mount weld. Last picture shows a crack developing. Are you towing with the jockey wheel retracted but in place? I remove mine for travel.

[Charlie M. (UH & 002 owner/pilot)]

While this is a thread I've done in an automotive forum, it gives some good basic engineering/hardware info......

http://www.newtiburon.com/forums/newbie-forum/284042-nuts-bolts-what-torque-why-should-i-care-not-talking-engines.html

Basically, it's about the plastic/elastic deformation of the grade/size hardware you're using and why a torque value is "approximate" based on many outside influences.

[howard banks]

Without having seen in person any of these failed bolts I am therefore guessing a bit -- and at some point in this long thread this may already have been said.
1. it is unlikely that the initial failure of these bolts was in shear. They actually came apart at the end in shear, but the initial failure was fatigue. When the growing fatigue cracks (typically growing inward from each side of the threaded section normal to the load) reduce the remaining unbroken area of the bolt to around the level of the load limit of the steel the bolt busts.
2. The first and most important thing when trying to avoid the problem is to buy decent quality bolts where the shank of the bolt is longer than the outside measurement of the tongue. The thread adds a notch factor which reduces the fatigue limit of the steel being used. Depending on how badly the threads are made (many are pretty rough at a microscopic level and the surface actually has what amount to many many small microcracks) the fatigue limit of the steel in shear is seriously reduced, easily by a half in many cases. Make sure the failure inducing threads are well outside the area where shear loading will occur. Preferably do not use washers to fill in the gap, but a proper spacer.
3. Do tighten the bolts to the correct amount as specified for the steel in question. As has been said in this thread often, an insufficiently tightened bolt is asking for the thing to break, even if of proper shank length -- as for different reasons is an over-tightened bolt.
PS: From personal experience the round tube tongue is clearly inferior to the square one when it comes to serious road overload, as in a sway that gets out of hand and ends in ugliness.




On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>
> http://www.foxonecorp.com/images/20160703_154501.jpg
>
> In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
>
> The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
>
> These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
>
> I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
>
> So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
>
> A few dollars in bolts might save you thousands in repairs!
>
> Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

[[email protected]]

If memory serves me ( 64 years since A&E school) to be considered airworthy; threaded portion of a bolt must never rest on the components of the joint, one washer under the nut is always necessary with a maximum of two washers, or use a shorter bolt. USAF A&E school, Witicha Falls, Tx 1952.
JJ

[Andrzej Kobus]

On Wednesday, July 20, 2016 at 10:31:52 PM UTC-4, Dave Springford wrote:
> Hi Tom,
>
> Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
>
> After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
>
> I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.

I just checked my new trailer (delivered this year), it has bolts 10.9.

[Tom Kelley #711]

On Thursday, July 28, 2016 at 2:59:28 PM UTC-6, Andrzej Kobus wrote:
> On Wednesday, July 20, 2016 at 10:31:52 PM UTC-4, Dave Springford wrote:
> > Hi Tom,
> >
> > Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).
> >
> > After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.
> >
> > I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.
>
> I just checked my new trailer (delivered this year), it has bolts 10.9.

To follow up on my earlier post. My trailer, as many know, is towed behind my motor home. Its on a 6 foot tow bar which goes under my motorcycle lift which then attaches to the bottom of the lift. This whole system does allow for movement as its subject to bouncing/flexing around when traveling. But I never have seen the trailer sway thru my rear view camera.
I again checked my bolts(10.9) and their is a washer then self locking nut installed. I did take my torque breaker bar to check. The head of the 2 bolts are really tight( I never went for a max torque reading), but both nuts had less than 25 pounds of torque applied.
I did tighten both nuts down and it appears the nylon used in the nut has worn allowing them to loosen(become looser or maybe that is what they were originally torqued to?).
My trailer is a 2006 and has around 80,000 tow miles on it. Have gotten new bolts,washers, nuts to carry with me.

Thanks again to Dave for bringing this to our attention.

Best. #711.

[[email protected]]

The bolt which sheared on my trailer was also a 10.9. As Howard noted above and I have stated earlier in the thread the threads were in the shear plane which I believe is the starting point for the troubles as the threads become distorted due to trailer tongue stresses during towing allowing the bolt to loosen which creates move movement which eventually ends in shearing.

David Martin
ASG29E BV

[howard banks]

Just to clarify what I tried to say above:
The failure in metallurgical terms was caused by fatigue. The load was in the shear plane. Threads in the actual load area do serious damage to the fatigue limit of the bolt. (Looking at a microscopic level at most threads, especially ordinary commercial ones, can be frightening.) The fatigue cracks originate in the bottom of the threads, typically diametrically opposed to each other and normal to the load plane. When the fatigued area gets to be large enough and the load exceeds the properties of the steel the bolt breaks.
If you have a failed bolt of this sort look at the fracture surface. There will typically be smooth area(s) that in moist circumstances are a bit rusty, or at least darker from oxygenation, and the final failure is much brighter in color. If it is clear from just looking that the fatigued area has tended to rotate and not just propagate in a symmetrical fashion, that indicates the bolt was not tight enough and was actually rotating slowly.
Since this particular failure is not happening once a month in the US, it suggests that the original bolt specification (as in 10.9) is adequate. The problem is that the bolts are not of adequate shank length. An easy thing to fix. Those lucky enough to have monster RVs (as in 711!) should just change the bolts at some regular interval.




On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>
> http://www.foxonecorp.com/images/20160703_154501.jpg
>
> In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
>
> The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
>
> These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
>
> I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
>
> So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
>
> A few dollars in bolts might save you thousands in repairs!
>
> Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

[Dave Springford]

>Preferably do not use washers to fill in the gap, but a proper spacer.

Hi Howard,

Could you elaborate on this? By spacer, I assume you mean a cylindrical block with similar diameter to a washer, but with the height of the cylinder equivalent to the stack of washers?

Why is this preferable to a stack of washers?

Thanks,

[Tom Kelley #711]

On Thursday, July 28, 2016 at 8:20:29 PM UTC-6, howard banks wrote:
> Just to clarify what I tried to say above:
> The failure in metallurgical terms was caused by fatigue. The load was in the shear plane. Threads in the actual load area do serious damage to the fatigue limit of the bolt. (Looking at a microscopic level at most threads, especially ordinary commercial ones, can be frightening.) The fatigue cracks originate in the bottom of the threads, typically diametrically opposed to each other and normal to the load plane. When the fatigued area gets to be large enough and the load exceeds the properties of the steel the bolt breaks.
> If you have a failed bolt of this sort look at the fracture surface. There will typically be smooth area(s) that in moist circumstances are a bit rusty, or at least darker from oxygenation, and the final failure is much brighter in color. If it is clear from just looking that the fatigued area has tended to rotate and not just propagate in a symmetrical fashion, that indicates the bolt was not tight enough and was actually rotating slowly.
> Since this particular failure is not happening once a month in the US, it suggests that the original bolt specification (as in 10.9) is adequate. The problem is that the bolts are not of adequate shank length. An easy thing to fix. Those lucky enough to have monster RVs (as in 711!) should just change the bolts at some regular interval.
>
>
>
>
> On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
> > On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
> >
> > http://www.foxonecorp.com/images/20160703_154501.jpg
> >
> > In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
> >
> > The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
> >
> > These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
> >
> > I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
> >
> > So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
> >
> > A few dollars in bolts might save you thousands in repairs!
> >
> > Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

Yes, Howard I hear you. Late this afternoon I removed the bolts and both bolts on the head side of the shaft showed excessive wear. Both bolts where the threads were riding in the holes showed excessive wear.
Went down to our nuts and bolt supplier and ordered new bolts with longer shafts so now both sides will ride on the shaft.
A regular inspection/replacement, along with having several spares, as we do with trailer tires, is a great idea.

Best. #711.

[Discus 44]

I have followed this post with quite some interest. I believe there is some additional information that has been missed however. The bolted joint in question uses M12 x 100 bolts with Nylon lock nuts. The actual joint couples a C channel and a square tube. The bolted joint is subject to transverse vibration forces which translates to shear once the joint has loosened. If the "locknut" nylon has become dry and hardened it may loosen as one is driving down the road and eventually separate. Then the bolt will fall out. Because both elements in the joint are "flexible" as in the square tube being hollow and the C channel can flex or distort some (called fretting) the eventual result is loosening of the fasteners. The design of the joint does include threads in the shear plane which is always a problem. Increasing the length of the fastener and adding washers to eliminate the shear in threads may help. Some of the posts have suggested using a "spacer" which I believe would have to be installed inside the square tube to act as a method to keep the joint from distorting and the prevailing joint torque from loosening as a result of the less flexible / compressible joint, however this would require drilling out the tube and potentially weakening the tube. One would have to probably weld this new spacer and of course it is a galvanized finish which has it's own hazards. And what diameter the spacer? If I have misunderstood the intent of the spacer idea, sorry. OK, so my answer is without significant engineering study, and experiments that could lead to an accident, I suggest checking the existing bolts and nuts for tightness and replacing them with at least 10.9 strength and new "locknuts".. The rated torque value for this bolt is 105 N-m or 77 Ft/lbs. Due to the forces translated to this joint this joint will loosen as the miles pile up. Checking the joint periodically should become part of the pre-towing checklist. Keeping a spare couple of bolts and nuts in the kit is also not a bad idea. I have seen on my own trailer the effect of the bolt necking as it was slipping around in the joint and I replaced it with new bolts and locknuts. Phew! I almost had the same experience as Dave. Just for more information If you look at Bolt Science.com for some interesting ways bolts fail. http://www.boltscience.com/

[2G]

On Tuesday, August 2, 2016 at 6:26:31 AM UTC-7, Discus 44 wrote:
> I have followed this post with quite some interest. I believe there is some additional information that has been missed however. The bolted joint in question uses M12 x 100 bolts with Nylon lock nuts. The actual joint couples a C channel and a square tube. The bolted joint is subject to transverse vibration forces which translates to shear once the joint has loosened.. If the "locknut" nylon has become dry and hardened it may loosen as one is driving down the road and eventually separate. Then the bolt will fall out. Because both elements in the joint are "flexible" as in the square tube being hollow and the C channel can flex or distort some (called fretting) the eventual result is loosening of the fasteners. The design of the joint does include threads in the shear plane which is always a problem. Increasing the length of the fastener and adding washers to eliminate the shear in threads may help. Some of the posts have suggested using a "spacer" which I believe would have to be installed inside the square tube to act as a method to keep the joint from distorting and the prevailing joint torque from loosening as a result of the less flexible / compressible joint, however this would require drilling out the tube and potentially weakening the tube. One would have to probably weld this new spacer and of course it is a galvanized finish which has it's own hazards. And what diameter the spacer? If I have misunderstood the intent of the spacer idea, sorry. OK, so my answer is without significant engineering study, and experiments that could lead to an accident, I suggest checking the existing bolts and nuts for tightness and replacing them with at least 10.9 strength and new "locknuts". The rated torque value for this bolt is 105 N-m or 77 Ft/lbs. Due to the forces translated to this joint this joint will loosen as the miles pile up. Checking the joint periodically should become part of the pre-towing checklist. Keeping a spare couple of bolts and nuts in the kit is also not a bad idea. I have seen on my own trailer the effect of the bolt necking as it was slipping around in the joint and I replaced it with new bolts and locknuts. Phew! I almost had the same experience as Dave. Just for more information If you look at Bolt Science.com for some interesting ways bolts fail. http://www.boltscience.com/

There is one simple solution to bolted joints losing their preload tension (which is what torquing accomplishes): use Belleville spring washers in place or in addition to the flat washers. The washers maintain constant preload tension over a wide range of conditions.

Tom

[JS]

Thanks for posting this Dave.

Finding bolts with the right unthreaded length wasn't easy. Just replaced the 8-year-old 10.9 grade bolts with AN8-36A and AN365-820A from Aircraft Spruce. $20 with spares and shipping. AN8-37A bolts would work too. The unthreaded part is long enough and the threaded part comes to the top of the Nylock when using locknuts.
Torqued to 45Lb. Does that seem right?

The old bolts didn't look bad. A little corroded, but still tight. The threaded part was not damaged but too long. The unthreaded part was too short for the job.

Do this at home! Chock the trailer. Jack up the tongue aft of the bolted connection. Release the parking brake. 19mm fits metric and STD. Loosen both. Change one at a time, and don't tighten until it's reassembled as the AN8 bolts are a snug fit.
Jim

[RuudH]

I was lucky to discover the sheared forward bolt before my 1200 km trip to the French Alps this spring
This bolt was exactly the same position as in your picture. Only the head was gone, with the rest of the bolt still in.

https://dl.dropboxusercontent.com/u/35654093/cobra-bolts.jpg

I changed both bolts with original ones and installed them with the correct torque.
My Cobra trailer was build in 2006, holds a Duo Discus xT and weighs 1300 kg.
Average mileage is about 5000 km per year.

I think best practice is to change these bolts at regular intervals ( every 4-5 years?)





Op donderdag 7 juli 2016 23:21:21 UTC+2 schreef Dave Springford:
> On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture here:
>
> http://www.foxonecorp.com/images/20160703_154501.jpg
>
> In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.
>
> The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.
>
> These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.
>
> I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.
>
> So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.
>
> A few dollars in bolts might save you thousands in repairs!
>
> Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

[Ian[_2_]]

On 08/08/2016 08:26, RuudH wrote:

> I was lucky to discover the sheared forward bolt before my 1200 km trip to the French Alps this spring
> This bolt was exactly the same position as in your picture. Only the head was gone, with the rest of the bolt still in.
>
> https://dl.dropboxusercontent.com/u/35654093/cobra-bolts.jpg

That photo shows a classic fatigue failure. But it has failed through
the shank not the threaded portion. Rather it appears to match the
corrosion marks on the remaining bolt. It also looks like the brittle
fracture area is quite a large portion of the total area, which implies
that it is quite highly stressed.

Solution? Bigger bolts, more bolts or stronger bolts, or all of these.

Ian

[Casey[_2_]]

I'm no engineer, but seems to me the length of the coupler puts additional stress on bolts. Seems to me that if the bolts were closer to the hitch then there would be less stress on them by a lever type action. I've towed heavier boats with trailer couplers similar to this but rated for 5000lb: https://www.zoro.com/fulton-trailer-coupler-class-ii-3500-lb-22300-1256/i/G3226027/ and you can see the couple is much shorter.

Of course the design with the break away and brake would have to be engineer differently.

I like the idea of Cobra having galvanized tongue but wonder why they did not use galvanized bolts.

[[email protected]]

Seems like there should be some thought towards using a different type of tongue on trailers that are being towed by RVs and motorhomes.
The tongues used on automobiles that are towed behind RVs allows the tongue to move up and down. Seems like that would eliminate most of the forces that are overstressing the mounting bolts on our glider trailers being towed behind vehicles that have a long distance between the rear axle and the tow ball.

[[email protected]]

I see your point, but towed autos are sitting on 4 wheels and therefore a hitch that allows vertical movement works. Try that on a 2 wheel trailer and the front of our glider trailers would emediatly drop to the ground.
JJ

[[email protected]]

Aw. Details.

[[email protected]]

On Wednesday, August 10, 2016 at 2:41:33 PM UTC-4, wrote:
> Aw. Details.

If you're worried about the trailer tongue dragging with a flexible trailer hitch, just leave the front dolly wheel in the "down and swiveling" position while trailering. Might want to upgrade the bearing on it, though. :)

Chip Bearden
ASW 24 "JB"

[Casey[_2_]]

Just wondering if this type of trailer tongue design would be any better for large motorhomes? Has anyone had a failure with this type tongue while towing with a large motorhome?

https://www.dropbox.com/s/4vva44n0ho6zazj/IMG_0495.JPG?dl=0

[Vaughn Simon[_2_]]

On 8/15/2016 11:16 AM, Casey wrote:
> Has anyone had a failure with this type tongue while towing with a large motorhome?

I once had a failure with that style tongue, and I was towing with my car!

In my experience there is nothing inherently superior about a double
trailer tongue. Regardless of style, the adequacy of any trailer tongue
is all about the engineering and construction. As always, the devil is
in the details.

[[email protected]]

My failure was at the actual hitch not the tongue. I had two failures actually, one with the original hitch from Cobra and the second on a replacement hitch from autozone. the euro hitch has one vertical and one horizontal bolt, the replacement had two horizontal and one vertical bolts I had to use one of the vertical bolt holes away from the tow vehicle and drill the horizontal hole in a different location to make it fit the failure was in the vertical bolt hole, and the hitch " ripped" the metal away. Luckily the horizontal one held. My latest design, I doubled the hitch plate with 1/8" steel "U" channel and drilled out to match the tongue. 1/2" bolts still one vertical one horizontal and so far so good.

[Muttley]

On Wednesday, August 10, 2016 at 8:23:53 PM UTC+1, wrote:
> On Wednesday, August 10, 2016 at 2:41:33 PM UTC-4, wrote:
> > Aw. Details.
>
> If you're worried about the trailer tongue dragging with a flexible trailer hitch, just leave the front dolly wheel in the "down and swiveling" position while trailering. Might want to upgrade the bearing on it, though. :)
>
> Chip Bearden
> ASW 24 "JB"

would not recommend this, as I had a dolly wheel smashed up by high speed bumps, since then dolly wheel is always removed for long travel trips.

[2G]

On Monday, August 15, 2016 at 1:01:57 PM UTC-7, wrote:
> My failure was at the actual hitch not the tongue. I had two failures actually, one with the original hitch from Cobra and the second on a replacement hitch from autozone. the euro hitch has one vertical and one horizontal bolt, the replacement had two horizontal and one vertical bolts I had to use one of the vertical bolt holes away from the tow vehicle and drill the horizontal hole in a different location to make it fit the failure was in the vertical bolt hole, and the hitch " ripped" the metal away. Luckily the horizontal one held. My latest design, I doubled the hitch plate with 1/8" steel "U" channel and drilled out to match the tongue. 1/2" bolts still one vertical one horizontal and so far so good.

Sometimes what happens is a design fails and you strengthen the failed part, only to discover that the next weakest part of the design fails. This is the epitome of a "bandaid" fix. The whole system needs to be analyzed to find an engineered solution.

Tom

[JS[_5_]]

On Thursday, September 8, 2016 at 9:32:24 PM UTC-7, 2G wrote:
> On Monday, August 15, 2016 at 1:01:57 PM UTC-7, wrote:
> > My failure was at the actual hitch not the tongue. I had two failures actually, one with the original hitch from Cobra and the second on a replacement hitch from autozone. the euro hitch has one vertical and one horizontal bolt, the replacement had two horizontal and one vertical bolts I had to use one of the vertical bolt holes away from the tow vehicle and drill the horizontal hole in a different location to make it fit the failure was in the vertical bolt hole, and the hitch " ripped" the metal away. Luckily the horizontal one held. My latest design, I doubled the hitch plate with 1/8" steel "U" channel and drilled out to match the tongue. 1/2" bolts still one vertical one horizontal and so far so good.
>
> Sometimes what happens is a design fails and you strengthen the failed part, only to discover that the next weakest part of the design fails. This is the epitome of a "bandaid" fix. The whole system needs to be analyzed to find an engineered solution.
>
> Tom

Bringing this thread back up as another thread about towing with smaller cars hints at the subject.

The AlKo trailer tongue on many trailers has a placarded limit of 100kg.
Some are rated 80kg.
Don't overload the tongue if you don't want it to fail.
In the case of smaller vehicles, this also avoids overloading the rear of the tow vehicle, perhaps putting too little weight on the steering axle.
If you need to carry more weight, put some elsewhere, perhaps in a drawer below the trailer, a Cobra option, or an IMI retrofit. I've installed both.
My last drawer install successfully took the tongue weight of a trailer down from close to 400 pounds to below 220lb / 100kg with the same load on board.
Jim

[Papa3[_2_]]

On Friday, March 2, 2018 at 10:57:50 AM UTC-5, JS wrote:
> The AlKo trailer tongue on many trailers has a placarded limit of 100kg.
> Some are rated 80kg.
> Don't overload the tongue if you don't want it to fail.
> In the case of smaller vehicles, this also avoids overloading the rear of the tow vehicle, perhaps putting too little weight on the steering axle.
> If you need to carry more weight, put some elsewhere, perhaps in a drawer below the trailer, a Cobra option, or an IMI retrofit. I've installed both..
> My last drawer install successfully took the tongue weight of a trailer down from close to 400 pounds to below 220lb / 100kg with the same load on board.
> Jim

Another trick. I relocated the spare wheel/tire (approx 7kg) from the mount inside the trailer at the glider nose-cone. I made an under-trailer mount with a steel plate and bolt pattern to match the rim. It sits just behind the axle, so it has very little moment and is also below the trailer's vertical CG. Bought a nice tire cover with elastic closure to keep the mud and grime off of it. Works great. A little less convenient to access, but makes the front of the trailer much more usable, especially with the short wingtips mounted in the front of the trailer.

[[email protected]]

Bolted under the trailer! So if the tyre in-use tyre has burst and the trailer has sagged down you may have to go under a jacked up trailer to unbolt it. I have done that - once - never again. Very frightening when trucks pass and the trailer sways.

An under-trailer wheel should go in some sort of cradle that it can be slid out of. Failing that carry a very stable axle stand.

[Papa3[_2_]]

Nope. Thought about that. Plenty of room to drop it without needing to jack up the trailer first, even with one tire down. Worst case can unhook the hitch, chock both wheels, and drop the front end. Lots of clearance that way.

[Bob Kuykendall]

On Friday, March 2, 2018 at 10:39:45 AM UTC-8, Papa3 wrote:
> Nope. Thought about that. Plenty of room to drop it without needing to jack up the trailer first, even with one tire down. Worst case can unhook the hitch, chock both wheels, and drop the front end. Lots of clearance that way.

I once drew up plans for a spare tire post for a Cobra that locates the spare on the side of the trailer, just forward of the right fender. As I recall, it bolted to reinforced areas already in the underside of the trailer bed, with maybe one extra hole required. I wouldn't be averse to fabbing a couple of them.

--Bob K.