PSA: Rivets went AWOL - Disaster avoided

Grumpy_G

The other day I was crawling around my trailer checking things over and found this : 



All four of the rivets connecting the tongue (right side of pic) to the main trailer frame went AWOL. I did check for cracks in the area when I got the trailer close to a year ago and they were definitely present. Somewhere along the last 2500-3000 miles I dragged it around they have failed. I did find all four inner pieces in the channel or the underbelly. 



It's an easy fix, drill the holes to 3/8 and use grade 8 hardware tightened to 5 ugga-dugga with a 3/8" impact gun. 



FWIW, this trailer is a 2015 and was owned by Dale before me. I know he put quite a few miles on it and it's anybody's guess why that happened. Just keep an eye on it .... 

ScottG

Yikes. That inspired me to run right out and check my own 2015. (All good!)

fstop32

Waiting for the thunderstorm to pass then I'll be running out to check my 2015...

Grumpy_G

The engineer in me needed to know what type of rivets these are: https://www.hansonrivet.com/lockbolts/maxlok-lockbolts-and-collars/

The collars are not broken off flush but 2-4 mm below the contact surface. Makes me wonder if the collar was not clamped on sufficiently. 

GigHarborTom

Rivets, Holly C___. That is not quality construction a tall.

Grumpy_G

I'm guessing the "maxlok" fasteners are faster and/or cheaper to install than regular grade 8 bolts. The tensile strength of a 1/4" lock bolt is 2600 lbs (according to the data in the link), the 3/8 grade 8 bolts I put in have 6900 lbs clamp load. 

AnOldUR

Grumpy_G said:

The collars are not broken off flush but 2-4 mm below the contact surface. Makes me wonder if the collar was not clamped on sufficiently.

Could breaking below the contact surface be caused by over torquing causing stress in the little 6mm bolt bolt?

Dutch061

I am sorry, but there is a big difference in "Tensile Strength" and "Clamp Load". While Tensile strength determines the fracture point of the fastener, it is "Proof Strength" that is used for torque specifications. "Clamp Load" is the desired end result of the fastener being tightened and has a list of variables that can affect it that is a long paragraph.

Bottom line, you can have the "correct torque" but have an incorrect "clamp load". The clamp load can be too high or not high enough, either of which is not a good fastener installation. 

It is very possible that the "tensile stiffness" of the "Huck Fasteners" is what the design engineer for the frame wanted to have some flexibility. Huck bolts are installed using a tool that stretches the bolt and crimps the "nut" at the same time to create the "clamp load". It is possible that there were tool issues or the person installing them was not properly trained, and they were "over stretched" which is likely why they failed.

Granted, it is a problem since they failed, that point there is no dispute on.

Brad

Grumpy_G

Dutch061 said:

I am sorry, but there is a big difference in "Tensile Strength" and "Clamp Load". While Tensile strength determines the fracture point of the fastener, it is "Proof Strength" that is used for torque specifications. "Clamp Load" is the desired end result of the fastener being tightened and has a list of variables that can affect it that is a long paragraph.

True, the maxlok site doesn't list clamp forces though and I merely wanted to highlight that 3/8 grade 8 bolts' normal operating forces are beyond the breaking limit of the maxlok. Tensile strength of the bolt is over 11000 lbs compared to 2600 lbs for the maxlok fastener. 

Seeing that Huck markets how fast these can be installed I have a suspicion why lock bolts are used .... 

AnOldUR

I'm not an engineer, but it looks like these bolts were only meant to sandwich the two frame components together. The dimples in the frame look like what would stop movement and prevent shearing of the bolts. I'm guessing that the bolts may have been over tightened causing "over stretched" bolts mentioned by @Dutch061.

I put in a ticket with nuCamp. It will be interesting to hear if/what they say.

Denny16

Also, nüCamp does not make the frame, they buy the frames from a outside manufacturer, and get the frames already assembled.  

Cheers 

ChanW

Hmmm. Thanks for the heads-up, Grumpy.

Will be crawling under the Tab today!

Michigan_Mike

There are a lot of dynamic forces that occur during road travel, flexing, twisting, bouncing, etc.  Would this be a result of the above and via loading on the tongue of the trailer with items like generators, gas cans, gear, etc.?  

Tabaz

Same thing happened to my August 2015 build 320 about two years ago.  Took it to a trailer shop and they replaced the rivets with bolts.  

AnOldUR

@Tabaz do you remember what size bolts they used? Also, did you contact nuCamp?