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Rod bolt stretch

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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Is there any tips for stretching rod bolts? I'm using manley tri beam rods with arp 625+ fasteners. It says ".0065-.0075" recommended stretch using 55-60ft lbs of torque. I applied the arp lube to the threads and under the cap. Installed the bolts and used the 60ft lbs of torque and got about .0050''-55'' of stretch. Then backed off the bolt and re torqued and reached .0065''-70''. Is this normal to get to target stretch?

You may find that new bolts take a few torque cycles to achieve consistency in the relationship between torque and stretch. This is why stretch is a superior method because it's the stretch we really care about, not the torque. I'd say that if you repeat the test 4-5 times you'll find the torque settles down to a fairly consistent value to achieve your target stretch.

Thanks for that tip. I am going to try that and would you suggest doing this for the head studs? Torque cycle the new studs a few times to get a more "accurate" torque value.

It certainly can't hurt.