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1931 Plymouth 4 Cylinder engine torque specifications


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Near as I can tell, there were no cylinder head torque numbers published for Plymouth prior to the mid-1930s. And the engines being built then were quite different from yours. The 1928 Q through the 1932 PB all used the same stud, part number 303773. The 1929 U through 1932 PB all used the same nut, part 50079 which does not show up in the standard parts section of the parts book. However the 1928 Q used part 120370 which is a 7/16-20 free fit cad plated nut. So I guess the studs for all those cars were 7/16-20 thread at the nut side.

I don't know when they started using special hardened fasteners for cylinder heads, but I'm pretty sure that they would not have been using anything that exceeded grade 5 back then. Looking up the torque specifications for a modern grade 5 7/16-20 bolt I find a dry torque of 55 ft-lbs and a lubricated torque of 40 ft-lbs. It is quite possible that they did not use studs that were up to modern grade 5 standards, so those values might be a bit high.

For the rest of the engine, I'd probably just go through the same exercise: Look at the fastener size, guess at the grade of material used and then lookup the torque values in a machinists manual.

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