Quote:
Originally Posted by Pete
Here are few things to think about for head studs.
A thread to be properly used needs to be CLEAN bare metal.
No corrosion, rust or scale. Any of these will corrupt a torque reading.
A thread chaser is essentially an under size tap which will clean out MAJOR rust and corrosion. This device can not produce a correct size CLEAN thread. Like it or not, the laws of physics apply here.
Head stud holes in a block need to be cleaned with a standard tap which will make the thread size as it came from the factory. This operation needs to be done with a fixture that holds the tap in perfect vertical alignment or a machine such as a mill or large drill press.
If the hole does not clean to bare metal then it is too rusted/corroded to hold proper torque and needs to be repaired.
While sometimes not visible, corrosion can account for up to 20% corrupt torque readings before the thread fails.
A sealer such as high temp. RTV can be used on the dead end but a thread lube absolutely must be used on the fine thread end. The sealer should be allowed to dry for at least an hour before assembly.
Head stud holes in a block can be tested before final assembly of the engine with simple home made tools. A 3 inch diameter by 2 inch thick steel slug (BOTH SIDES PARALLEL) with a 1/2 inch hole in the center, a HEAVY HARD steel 7/16 washer, a HARD high nut and a proper length stud. You install the stud through the slug with the lubed nut and washer on top and torque to 80 for a model A or flathead V8. If the thread is good, the torque wrench will have a solid feel. No “floating” or wanting to keep turning.
Good threads will easily go over 100 if you are wondering.
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Some excellent info here, especially that last sentence in red?
Thanks, Gary in N.Y.
P.S. We actually test ALL the head bolt holes when we mount the block plate either during a pressure test session or for finish honing the bores, but they ALWAYS get checked way before the final assembly time! Occasionally we'll do singles also (photo below).