Lock washers, self-locking nuts, cotter pins, and even safety wire are for people too timid to put the proper torque on bolts. Properly-lubricated and tightened bolts and nuts do not get loose and back off. If you use a higher grade bolt than what was used originally, be aware that any factory torque specification you find will be far too low to keep the fastener tight. A bolt has to stretch a certain percentage of its length to stay tightened properly, and if a Grade 8 bolt is used in place of a Grade 5, for instance, you MUST look up the proper torque value for the grade 8 and tighten accordingly.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!