One critical bolt missing!

Steve Barnes · #1 09-07-2015, 01:23 PM

Went to move my RV6 in the hangar and one wheel had a point of very bad resistance while rolling. It would catch and let go while rolling it around. It felt like a disc was badly bent. Further inspection revealed that one of the three #4 bolts that hold the rim halves together was totally missing and the halves pulled away a little. (I know what you are thinking. NO I didn't forget to put it in). Somehow it must have broken and both parts of the bolt/nut were missing (probably at the bottom of someones swimming pool).

Here's my thoughts; I probably have under torqued the bolts thinking that the tire pressure would do that. If there was a little working room for the bolt/nut to move because of under torqueing it may have caused the nut to break at the threads.

Anybody else have this happen or any ideas.

Steve Barnes Owner of Fairings Etc.

BillL · #2 09-07-2015, 01:40 PM

If a bolt is holding a 1000 lb weight, an eye is on bolt end, a different eye is on the nut end. a washer is in between. You torque the bolt with an initial tension of 1000 lbs. Now you lift the weight.

What is the tension load on the bolt?

BobTurner · #3 09-07-2015, 01:55 PM

For any weight, 0 to 1000 pounds, the tension on the bolt is unchanged. Heavier weights will start to stretch the bolt, increasing tension. It acts just like a strong spring, with the washer allowing extention but not contraction.

Steve Barnes · #4 09-07-2015, 01:56 PM

That is what I was thinking Bill. With the tire pressure the rims may have slightly pulled apart with bolt stretch with out enough torque being applied. So the question is; torque the bolt before or after the tire is inflated?

Steve

alpinelakespilot2000 · #5 09-07-2015, 02:24 PM

Note also, at least if you have the same Cleveland wheels that I do, that the torque specs for the AN4 bolts are quite a bit higher than normal.

Mel · #6 09-07-2015, 02:45 PM

Quote:

Originally Posted by Steve Barnes

That is what I was thinking Bill. With the tire pressure the rims may have slightly pulled apart with bolt stretch with out enough torque being applied. So the question is; torque the bolt before or after the tire is inflated?
Steve

Before!!!!

BillL · #7 09-07-2015, 04:23 PM

Yes, it is 1000lbs, the load simply transfers from the washer to the external load. Bob had a good physical description. And like Mel says "Before!"

Just replace the bolts and torque to the wheel manufacturer's specification.

David Paule · #8 09-07-2015, 04:38 PM

Not exactly, although that's the common expectation.

For the shank portion of the bolt -what's happening is that the axial stiffness of the entire joint (bolt plus washer) carries the load. The bolt will carry a share of the load based upon it's fraction of the total axial stiffness, in addition to the preload, which the shank alone carries (the washer being in compression from the preload). Of course this is before separation.

I've seen that fraction typically be in the range of 10% to 20% but of course it'll vary considerably depending on the joint's geometry.

After separation the bolt carries the entire load.

Dave

BillL · #9 09-07-2015, 04:46 PM

Quote:

Originally Posted by David Paule

Not exactly, although that's the common expectation.

For the shank portion of the bolt -what's happening is that the axial stiffness of the entire joint (bolt plus washer) carries the load. The bolt will carry a share of the load based upon it's fraction of the total axial stiffness, in addition to the preload, which the shank alone carries (the washer being in compression from the preload). Of course this is before separation.

I've seen that fraction typically be in the range of 10% to 20% but of course it'll vary considerably depending on the joint's geometry.

After separation the bolt carries the entire load.

Dave

I agree Dave, I did not want to provide a complete analysis of abutment, but the OP was concerned he had over stressed the bolt from the load (tire pressure) and thus was considering lowering the preload (torque). Clearly, this is one of the few applications of a grade 5 bolt that is designed for a tension load and not a shear loading. The example was an attempt to illustrate that lowering the torque was not appropriate.

BobTurner · #10 09-07-2015, 05:19 PM

Quote:

Originally Posted by David Paule

Not exactly, although that's the common expectation.

For the shank portion of the bolt -what's happening is that the axial stiffness of the entire joint (bolt plus washer) carries the load. The bolt will carry a share of the load based upon it's fraction of the total axial stiffness, in addition to the preload, which the shank alone carries (the washer being in compression from the preload). Of course this is before separation.

I've seen that fraction typically be in the range of 10% to 20% but of course it'll vary considerably depending on the joint's geometry.

After separation the bolt carries the entire load.

Dave

Yes, I agree. My statement was correct only if the washer is incompressible - which, compared to the steel bolt, is not likely a good approximation.