[zakthor]

Reading Carroll Smiths book "nuts, bolts, fasteners and plumbing handbook" and have a few questions.

First, apparently split lock washers are useless. I also looked on the internet and there is a nasa fastener guide that agrees they are the same as flat washers once tightened. I suppose there is an assumption about application (sufficiently ridgid joint?) I dunno. I'm asking because my Yakima bike rack bolts to my hitch, the bolt kept loosening which made the rack sway and rattle. No amount of tightening would prevent it. I added a split lock washer under the existing washer and its not loosened for more than a year. Question is when is a lock washer useful? It seemed to save my bacon. I'm assuming the joint design is bad in some way that means the normal rules aren't valid (slight motion? Rack steel too soft?)

Second, nylocks for 911 valve covers are allegedly single use. These go on with very little torque. I can see the plastic on used nuts has been cut by the thread. Carroll smith says they are good because they can be reused "many times" Why can't valve cover nuts be reused? Supposedly good to 250f, is the 911 motor application too hot?

Thanks!