Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Re: Torx Problem
That point about a lock washer effectively turning into a flat washer is something I've pondered on several occasions. The only thought I can offer is that, due to the way the washer is formed, it acts like a ratchet in the tighten direction. Split lockwashers aren't split perpendicular to the plane of the washer, they're split at an angle that forms a knife edge on each side of the split. That edge is oriented so that the metal will pass over it more easily during tightening than loosening.
The points on a star lock washer are twisted the same way, so that the nut will slide over the edges of the star during tightening, but dig in when it's loosened.
That would mean that the lock washer doesn't really come into play until the fastener starts to back off. That might suggest that it won't help keep the joint tight, but if it starts working with only a couple degrees of reverse rotation, that shouldn't really result in a loose nut - it just allows a little of the stretch (preload) out of the bolt. One would hope that the engineers who figure out such stuff have that worked into the torque tables.
And the burr you mention is something I've seen many times, but dug up in the reverse direction, not forward.
If they really didn't do anything, Generous Motors wouldn't keep buying them and putting them on their vehicles.
You're absolutely right, of course, about the lubricated threads. Every torque spec I've ever seen has a footnote something like "Clean, undamaged threads lubricated with a light film of oil."