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Yield strength ratings on bolts and studs?

545 Views 3 Replies 2 Participants Last post by  MusclecarNeal
Per ARP the rating is 75% of the yield of said bolt or stud meaning studs with a torque rating of 85 ft.lbs. is actually 75% of full yield. Although this gives some stretch flexibility couldn't this also be a thorn in the side? My problem with the steel shim gaskets and need for a retorque could have some merit here.
Roughly 114 ft.lbs. would put them at 100% yield. Could it be since most of us follow the mfg. specs and torque to 85 ft.lbs. that we are actually giving some room for spring-back? This is good in a way as a safety valve to keep you from hurting a piston or ring by letting the heads lift but for max power without problems wouldn't going to 90%-95% put you closer to the stud yield and make the clamping force be more rigid? I know it would be taxing the studs some but what doesn't get stressed dunno

This would put it at 105-110 ft.lbs. Any dangers here?
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The last time I spoke to an engineer from ARP ( I was a WD for them at one time) we had a long talk about the yield strength and torque specs. We also spoke about bolt and stud stretch. The conversation included the reasons for why the specs are what they are and why. The bolt or stud must be stretched to provide clamping force. If the bolt or stud is stretched too much it losses its ability to clamp effectively as the elasticity is reduced. Remember that once an engine is warmed up the heads and block grow a little and stretch the fasteners more, that is why you sometimes find that you need to re-torque. Once the fasteners have stretched after being tightened and loosened 3 times they tend to stay were they were. Most people don't follow ARP's recommendations and don't tighten and loosen the fastener 3 times to spec begin with. I have had great luck by following the advice ARP gives and have had no head sealing problems in any of the ARP equipped engines we build. To add one thing about over-tightening fasteners. Did you ever think about the bore distortion that it causes, the deck distortion, the cylinder head distortion? It lends that deck and head distortion from over-tightening can cause more problems that over-tightening my solve. Also unless the cylinders were honed with the deck plate that that level with the exact same set of bolts they sure are not round when you do this.

Just my .02, your results may vary.
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Good points. I torqued mine twice so maybe I just need to do it one more time. This is the first motor I put studs in but I swear the instructions that come with the studs made no mention of doing it three times. I guess I will just make it a rule of all.
Remember, loosen ( back it off a little) then re-torque, that is what the engineer suggested. Has always worked well for me. Godd luck!!
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