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Use existing piston rod to crank nuts and bolts?

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J

John_Progess

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Having already installed the piston rods to crank shaft using the old nuts and bolts, I started thinking if I should have replaced them. It is not too late as the engine is sitting on my shop floor ready to be painted. The bolts looked perfect but the nylock nuts is really what I questioned. This is not a race car and the engine has been totally rebuilt. Any opinions from the group? Thanks and have a good day!

John
 
Replace them! Nyloc nuts are use-once-only in any case (and I really DISLIKE them on connecting-rod big ends, since it's impossible to get a true torque measurement) and it's really not worth taking a chance on the bolts. Maybe OK, but while the engine's out, buy some peace of mind.
 
+1
 
"Nyloc nuts are use-once-only in any case (and I really DISLIKE them on connecting-rod big ends, since it's impossible to get a true torque measurement)"

Not true, but it requires a bit of fussing to get the proper torque. One has to use a beam or dial reading torque wrench to read the running torque of the nyloc nut before it bottoms out on the bolt, then do the final torque to the pecified torque minus the running torque of the nut. This was the procedure for years when using nyloc fasteners on any critical assemblies on nuclear submarines. That said, the procedure was dropped a number of years ago when it was finally realized that the running torque was less than the tolerance for the final torque.

As for the replacement of the big end bolts - unless you can accurately measure the amount that the old bolts have stretched and can find a spec that tells you what is n acceptable amount (non existent as far as I know), replace them. When the cost looks to be too much, consider the cost of replacing the entire engine because a bolt broke at 4000rpm and allowed the rod to go through the side of the block (I can send you pictures of what a block out of a MGTD looks like when that happens). That consideration will put the price of new big end bolts from APT in perspective.
Cheers,
 
Hello John Progress, it's cheap insurance to change them especially as how they are accessible.

Regards,

bundyrum.
 
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