Head bolts

[Farmall MD nut]

I'm in the middle of an Fmall F-12 engine rebuild, and what I wanted to do is use head studs instead of bolts. My question is, will stainless hold up? It will be higher compression than stock. Doug

 

[Anonymous-0]

I think the biggest consideration is the tensile strength of the two materials. When you torque something, the goal is to stretch the fastener and the tensile strength of the fastener wants to pull it back together- that's where the "clamping pressure" comes from. The torque value on the F-12 be 90 ft. lbs and with the original bolt it would stretch say .030". Your replacement stainless fastener, if it has a higher tensile strength may only stretch .018" given the same torque. (Those numbers are for illustration only) Does that make sense?
Crucial also is turning all that torque from your wrench into clamping pressure. Any torque lost to friction with bad threads, paint, dry threads, etc. results in less clamping pressure (also known as preload).
How much are you going to increase the compression ratio?

Grub

 

[jmixigo]

I would recomend against stainless for head studs. Even when useing antisieze the threads tend to gall, and that throws torque values vs clamping force all outa whack. The thermal expansion rates are also higher. Stainless when stretched wants to stay stretched, it has little spring value. Google up ARP fasteners, they specialise in engine hardware for hot rods and have a good reputation with engine builders of all sorts.

 

[Farmall MD nut]

Hi Grub. So wouldn't that be better if the s/s stretches less? It would be less stress on fastener, not?

"Crucial also is turning all that torque from your wrench into clamping pressure. Any torque lost to friction with bad threads, paint, dry threads, etc. results in less clamping pressure (also known as preload)."

I couldn't agree with you more. That's exactly why I like to use head studs, because you're torquing the nut and not a 4"-5" bolt that twists and doesn't get all that torque to the threads. I've always used the CAT headbolt grease to lube threads.

I'm not sure how much increase I'm gonna have. I'm still mulling around ideas. Doug

 

[Farmall MD nut]

jmixigo, I beg to differ. I've been a welder fabricator all my life, and when we bend stainless(weather it be 16 GA, or 1/4") in the brake, it springs back way more than steel does.
If I'm making a 90 degree bend, I don't have to set the brake much over 90 degrees(91-93 degrees roughly) when doing steel, but for stainless I have to set the limit switch a bit farther(94-96 degrees roughly). Doug