Cobra top hinge plate bolt failure

I think that all hardware store socket head cap screws are going to be
grade 8 or equiv. so I don't think you have to worry about that.

My bolt popped in the middle of the threaded length which apparently
is not where Andy's bolt broke. That supports my impression that it
is primarily a tension failure rather than a shear failure.

The type of clamp that I used successfully by myself is called a "Kant
Twist" 4 1/2" machinist clamp. These are sold at www.use-enco.com and
lots of other suppliers. So I'm not so sure that designing a special
clamp is needed. What does need designing is a scheme to get a
couple more bolts into that plate. The design is flawed and
dangerous.

Steve Koerner (GW)
www.wingrigger.com

On May 16, 8:08*pm, Steve Koerner wrote:
The type of clamp that I used successfully by myself is called a "Kant
Twist" 4 1/2" machinist clamp. *These are sold atwww.use-enco.comand
lots of other suppliers. *So I'm not so sure that designing a special
clamp is needed. * What does need designing is a scheme to get a
couple more bolts into that plate. * The design is flawed and
dangerous.

Steve Koerner (GW)www.wingrigger.com

Hmm - I planned to clamp with surfaces:
- bottom: grab the front inside the extrusion slot
- top: fix the angle on top of the alum frame
Nothing fancy, just a couple parts with holes
preventing clamping surfaces rotating and a bolt...

Did the kant-twist end fit inside the front's slot ?

Thanks,
Best Regards, Dave

On May 16, 5:18*pm, Dave Nadler wrote:
On May 16, 8:08*pm, Steve Koerner wrote:

The type of clamp that I used successfully by myself is called a "Kant
Twist" 4 1/2" machinist clamp. *These are sold atwww.use-enco.comand
lots of other suppliers. *So I'm not so sure that designing a special
clamp is needed. * What does need designing is a scheme to get a
couple more bolts into that plate. * The design is flawed and
dangerous.

Steve Koerner (GW)www.wingrigger.com

Hmm - *I planned to clamp with surfaces:
- bottom: grab the front inside the extrusion slot
- top: fix the angle on top of the alum frame
Nothing fancy, just a couple parts with holes
preventing clamping surfaces rotating and a bolt...

Did the kant-twist end fit inside the front's slot ?

Thanks,
Best Regards, Dave

Dave -- I am not really visulizing all this. Probably because I dealt
with it in the dark holding a flashlight. If you've worked through a
plan, it's probably a good one. It does seem like one of the jaws on
the clamp was fatter than I wished it were. So that is probably what
you are referring to. On my hinge plate, I was able to get the holes
to allign though even without the jaw stationed exactly where I wished
it would go. That might not be the case if the plate is positioned
just a little different on your trailer.

GW

It looks like YO and I were both commenting at the same time to the
effect that it is more likely a tension failure. However I don't
agree that the gas spring force has much to do with it. The gas
spring force is small compared to the strength of two 5/16 cap
screws. I suspect it has more to do with the inertia of the lid in
longitude with some combination of vibration and road bumping creating
the load. Heaven knows my trailer has seen some bumpy roads.

GW

On May 16, 5:23*pm, Steve Koerner wrote:
It looks like YO and I were both commenting at the same time to the
effect that it is more likely a tension failure. *However I don't
agree that the gas spring force has much to do with it. *The gas
spring force is small compared to the strength of two 5/16 cap
screws. *I suspect it has more to do with the inertia of the lid in
longitude with some combination of vibration and road bumping creating
the load. *Heaven knows my trailer has seen some bumpy roads.

GW

Examination of the failed bolt should tell you whether it was tensile
with necking or shear with a fairly clean break.
But, main concern I would have is having a failure while rolling down
the road and doesnt sound like something one could fix by themselves
even with a spare bolt on hand. Maybe the solution is to pre-
emptively replace these bolts anyways at say 10 years?

On May 16, 6:23*pm, joesimmers wrote:
Did the bolt break or shear at the location where the thread ends and
solid shank starts?

...

I think I would get bolts long enough to have a solid shank all the
way thru the structure causing the misaligned stress
you decribe and only enough thread on the back side to hold the washer
and nut.

But, note that the load is not just in shear.
These 4 bolts are taking the total force of the
compressed gas springs in tension...

Best Regards, Dave "YO electric"

On May 16, 7:40*am, Andy wrote:
Last year "YO" told us about how he nearly lost his trailer top after
both bolts securing one trailer top hinge plate failed. *Of course I
checked my bolts and all four were secure at that time.

Yesterday I arrived at the club field and had a problem releasing the
left rear top latch. *Sure enough the outer bolt on the left hinge
plate had failed and this allowed the top to move back slightly and
bind up the rear latch. *I was able to find replacement bolts at a
local hardware store. *5/16 x 3.5 inch *are very close to the
diameter *the original metric bolt and provide more load bearing
unthreaded shank.

The bolts in question go through the front handles, the trailer glass
top, the trailer top frame (with an internal spacer block), a spacer
plate, and then the main hinge plate. All the parts try to misalign
under load. *With the help of 5 people I was able to align all the
pieces well enough to get the new bolt in and was then able to rig and
fly the task.

Another isolated failure? *No. *While I was working on it GW walks up
and says he found the same bolt failed on his trailer the previous
evening. My trailer is 9 years old and GW's I think 10 years old.
Both are glass top but I don't know if that is significant. *So 3
known failures of these bolts.

Do you feel lucky?

Andy (GY)

This happened to a friend of mine also exactly as you describe. So
make that 4 cases.

On May 16, 7:40*am, Andy wrote:
Last year "YO" told us about how he nearly lost his trailer top after
both bolts securing one trailer top hinge plate failed. *Of course I
checked my bolts and all four were secure at that time.

Yesterday I arrived at the club field and had a problem releasing the
left rear top latch. *Sure enough the outer bolt on the left hinge
plate had failed and this allowed the top to move back slightly and
bind up the rear latch. *I was able to find replacement bolts at a
local hardware store. *5/16 x 3.5 inch *are very close to the
diameter *the original metric bolt and provide more load bearing
unthreaded shank.

The bolts in question go through the front handles, the trailer glass
top, the trailer top frame (with an internal spacer block), a spacer
plate, and then the main hinge plate. All the parts try to misalign
under load. *With the help of 5 people I was able to align all the
pieces well enough to get the new bolt in and was then able to rig and
fly the task.

Another isolated failure? *No. *While I was working on it GW walks up
and says he found the same bolt failed on his trailer the previous
evening. My trailer is 9 years old and GW's I think 10 years old.
Both are glass top but I don't know if that is significant. *So 3
known failures of these bolts.

Do you feel lucky?

Andy (GY)

Just checked my hinge plate bolts and they appear to be OK, but one
nut was just finger tight. A loose nut could/would lead to bolt
failure. Recommend we all check to make sure our hinge plate nuts are
tight.
JJ

On May 17, 11:04*am, JJ Sinclair wrote:
On May 16, 7:40*am, Andy wrote:





Last year "YO" told us about how he nearly lost his trailer top after
both bolts securing one trailer top hinge plate failed. *Of course I
checked my bolts and all four were secure at that time.

Yesterday I arrived at the club field and had a problem releasing the
left rear top latch. *Sure enough the outer bolt on the left hinge
plate had failed and this allowed the top to move back slightly and
bind up the rear latch. *I was able to find replacement bolts at a
local hardware store. *5/16 x 3.5 inch *are very close to the
diameter *the original metric bolt and provide more load bearing
unthreaded shank.

The bolts in question go through the front handles, the trailer glass
top, the trailer top frame (with an internal spacer block), a spacer
plate, and then the main hinge plate. All the parts try to misalign
under load. *With the help of 5 people I was able to align all the
pieces well enough to get the new bolt in and was then able to rig and
fly the task.

Another isolated failure? *No. *While I was working on it GW walks up
and says he found the same bolt failed on his trailer the previous
evening. My trailer is 9 years old and GW's I think 10 years old.
Both are glass top but I don't know if that is significant. *So 3
known failures of these bolts.

Do you feel lucky?

Andy (GY)

Just checked my hinge plate bolts and they appear to be OK, but one
nut was just finger tight. A loose nut could/would lead to *bolt
failure. Recommend we all check to make sure our hinge plate nuts are
tight.
JJ- Hide quoted text -

- Show quoted text -

I checked my bolts for security last year after YO's report. Don't
remember how much I tightened them, it at all, but the damage was
probably already done. I think the only safe action is to replace the
bolts.

Given Howard's confirmation of fatigue failure I wonder how much wash
boarded dirt roads are a factor. Is this just a Western US hazard? I
didn't even know what a wash board road was until I moved here.

Andy (GY)

On 5/17/2011 11:38 AM, Andy wrote:

I checked my bolts for security last year after YO's report. Don't
remember how much I tightened them, it at all, but the damage was
probably already done. I think the only safe action is to replace the
bolts.

Given Howard's confirmation of fatigue failure I wonder how much wash
boarded dirt roads are a factor. Is this just a Western US hazard? I
didn't even know what a wash board road was until I moved here.

Washboarded roads - maybe. Here's another data point: 1995 Cobra trailer
for ASH 26 E, 160,000 miles of highway driving, and the bolts are not
broken.

Some details:

*note that the ASH 26 E trailer body is 30 feet long, as the 18 meter
wing is only two pieces (tongue is another 4 feet)

*towed almost entirely by motorhomes

*I haven't actually pulled out the bolts to see if they are cracked

*Probably less than 1000 miles of dirt roads, including mostly roads
under repair or construction, and hardly any washboarded roads.

I will replace the bolts as soon as people settle on the best kind of bolt.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)