<VV> Steel bolts and fatigue

[kevin nash]

>
> All that having been said, it used to be that almost nobody ever
> bought new hardware when putting an engine together.? I never did, and
> never had any issues.?? Maybe the hardware isn't quite what it used to
> be... ??? This goes for head bolts, rod nuts, main cap bolts etc.?
> Likewise Corvair crankcase bolts and rod nuts.? None ever failed.
>
>
> Then there's the Cadillac Northstar 4.6 engines that still had head
> gasket failures even with all new head bolts/inserts etc... kinda hard
> to trust some of the modern engine hardware/designs. I did have one
> bigblock Mopar head crack after a few years following assembly but it
> wasn't because of reusing the head bolts (crack between chambers).?
> Maybe I just got lucky along the way?

Steel in most cases has an unlimited life if kept out of yield. Don't
actually stretch it so that it deforms, and don't let it rust/corrode,
and it keeps its strength.

Stretch it - take it past its yield point so it actually changes its
dimension, and - initially it gets stronger.

Yeah, those bolts you torque until they start stretching - they are
getting stronger.

Of course, at some point they start getting skinnier, and greater psi
doesn't compensate for fewer inches of cross section.

Jay Maechtlen
61 Corvair coupe
custom fiberglass skin
GM3800 supercharged
4T65E


Close, but not quite right. Steel has an unlimited life if its stretched to no more than 50% of its yield strength.
The reason fasteners can be reused (even though we shouldnt/not recommended/ect...) is because the
factory torque specs and bolt sizes had enough "overkill" that the bolts in most cases never get to this 50% yield point.

One example I can think of off the top of my head is the top cover bolt torques. I use 20 ft-lbs on these and have
never had even a tiny seeper type of oil leak doing it this way, but every single other engine was an oily mess
in this area using the stock bolt torques (half as much???)

Kevin Nash
63 EFI Turbo daily driver
Baddest most awesome cooling fan ever!

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