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Discussion Starter · #1 ·
So, to keep the story short, I had to remove the exhaust manifolds in the process of doing some other work on my firebird. I found that one of the manifold studs was broken in the block. The good news is that I was able to remove the broken stud, and now I want to put all new studs in when I put it back together. The problem is that the threads going into the block don't match the threads on the other end of the stud where the nut goes on to hold on the heat shield. I have to get a measurement yet, but I'm thinking the engine block side is english, and I know the other side is metric with a 1.25 pitch. Has anyone run into this before and know what the thread side on the engine block side is? And more importantly, I can't find any replacement studs to match the original studs. Any help or suggestions would be greatly appreciated!
 

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The engine side of the stud is 5/16-18 threads. Unless you buy new studs from GM, then bring your jar of Vaseline to cushion the shock , you'll have to go with 5/16-18 on both ends. Get grade 8 studs. And if your changing all of them, be advised there should be 2 different lengths of studs.

Some are about 1.10" long and some are about 0.85" long. This info was taken from 4th gen firebird parts book, so I can't attest to it's correctness. The lengths I give in "about" because diameter was given in inch size and length given in millimeters.

For all practical purposes 8mm and 5/16 are the same diameter. They are just threaded different.
 

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Discussion Starter · #3 ·
Thanks for the info! There are two studs still in the block on each side, the rest turned out with the nuts when I removed the manifolds. I was planning on replacing all of them so they'd all be the same threads, so good to know that some are different lengths as well.
 
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