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Posted by David Sherman on Monday, May 18, 2009 at 00:21:01 :
In Reply to: Re: Broken Beadlock Bolts posted by Will (in IL) on Sunday, May 17, 2009 at 23:12:54 :
I was thinking you were talking about combat rims. Yours is a whole different beast, so I don't know about it. The M37 combat rims have special bolts, but I've made my own by grinding off part of the head of a regular bolt. I've used grade 5 and they're holding up fine. I think they're 1/2".
If yours is some new contraption, maybe the people who make it are of the "grade 8 is always better than 5" philosophy. Could be a poor design. It would be interesting to know if there are fatigue cracks in any of your other bolts. If it was just one, I'd say it was a manufacturing defect, but two makes me think either it was an entire bad lot (wrong heat treat, embrittlement during plating, wrong alloy), which seems unlikely, or the bolt is the wrong choice for the application.
It seems to me that a good design for a wheel ought to be fairly foolproof. That means no fussy torque specs. Any monkey with a wrench should be able to torque them down good and tight and have them hold but not break. That means plenty of bolts, large diameter, with low stress on each. Maybe the this design was too "optimized" for a minimal number of fasteners and too demanding of precise installation.
This particular failure scares me -- partly because we don't know why they failed and it might be a bad design, and partly because if any one bolt fails, it increase the stress on its neighbors, which in turn are more likely to fail, and if they fail, there will come a point where even the perfect bolts will break or the bead lock will bend and the assembly will blow up.
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