Al-Ko Trailer Tongue failure

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

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"

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 he

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.

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 he

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.

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

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,

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 he

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.

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 he

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.

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/

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