I'm a machinist and industrial mechanic with over 35yrs of experience in industry and quite some emphasis on machine reliability.
Ideally nuts rely on bolt tension from elastic stretch to keep tight.
Aluminum thermal expansion throws havoc into this and is the reason we see necked down "stretch" headbolts on newer engines. The bolts stretch elastically like a spring to keep a tension even with high thermal expansion. If you have ever tried (I did) larger bolts on these engines, you know they don't work. The strength limit on the China engines is not the stud, but where it threads into the case, however the supplied studs are typically very prone to stripping and deformation.
I am not a fan of "shakeproof" or spring washers. They were originally invented to allow single wrench tightening on thru-bolt/nut installations, not for retention assurance. I was taught in college that hardened steel flat washers were the best answer in most cases. They spread the load and do not gall. Recently I have used Nord-Lock washers
http://www.nord-lock.com/nord-lock/wedge-locking/washers/introduction/ on industrial installations. Seen no failures but have no great history with them yet.
Studs can be loctited in place, but are a nightmare if sheared off flush with the case, unless heat can melt it.
Places where tension is essential like headbolts should just have standard nuts and flatwashers installed. Recheck torque often.
Light tension uses (clamping on thin tube, against rubber, etc) where not enough torque can be applied can use:
loctite,
double nuts,
lockwire,
single use Nyloc (if no heat), or
single use "distorted thread" locknuts if the stud or bolt is of good enough quality.
Spring or shakeproof washers will not help in light torque situations.
Steve
