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Torque dropping suddenly while tightening head studs

Practical Engine Building

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I was building up a 3sgte engine yesterday and was attaching the head with new ARP head studs. The head studs were tighten in several passes with increasing torque and everything was fine until the final pass to torque everything to ARP's spec of 60 lb-ft. On the final pass, a few of the bolts would suddenly give and turn at a much lower torque, almost feeling like something have stripped and takes maybe half a turn or more before reaching the proper torque again.

Could it simply be stuck threads simply getting unbinded? But all threads had been lubed with ARP ultra torque. Were the studs not bottomed fully and was moving while the nut was being torqued down? Since the instructions said hand tight only, I tightened down the studs with a 3/8 ratchet and held the ratchet on its head only with my full palm to limit torque but with sufficient force for a tight turn.

This sudden drop in torque really have me worried. Could something really have been stripped or could the studs have been stretched? I am definately taking them back out tomorrow and redo everything and hopefully I don't see threads from the block hanging on the studs.

At 60 ft/lb I would be very surprised if you've managed to strip any threads. I'd suggest removing all of the components and inspecting them to see if you can find a reason for this as it's not normal. Did you start by running a tap through the threads of the block before installing the studs? While the ARP instructions recommend hand tightening I do tend to go slightly further than this and I use an allen key and apply a small amount of force when tightening the studs.

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