Stupid bolt size question...

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Old July 15th, 2018, 05:19 PM
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Stupid bolt size question...

After an extended timeout, I'm finally ready to drop my engine and trans back in. Naturally a few miscellaneous bits have vanished in the meantime. Nothing major (knock wood), but I can't find the trans to block bolts, and I'd rather be sure on the size.

Anyone know the length of the six bolts? 425, TH400. TIA.
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Old July 15th, 2018, 06:05 PM
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3/8x16, probably 1 1/4 inched long
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Old July 16th, 2018, 07:10 AM
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I've used closer to 2" grade 8 bolts. Use hardened washers. I'm not familiar with the 425 block but the others use all open holes with lots of space so you can use long bolts.
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Old July 16th, 2018, 11:41 AM
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Originally Posted by oddball
I've used closer to 2" grade 8 bolts. Use hardened washers. I'm not familiar with the 425 block but the others use all open holes with lots of space so you can use long bolts.
All Olds engines use the same size bolts to mount the trans or bell housing to the block.
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Old July 17th, 2018, 06:23 AM
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Originally Posted by oddball
I'm not familiar with the 425 block but the others use all open holes with lots of space so you can use long bolts.

No, they don't. Five of the six holes are through holes. The one near the oil filter adapter is a blind hole on all 1964-1990 Olds blocks.
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Old July 17th, 2018, 07:41 AM
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Can I jump in on this thread ? Same topic - different bolts. I have a 1965 F-85 wagon that someone put a chev 305 in with welded mounts. All of that is now removed and I'm installing an Olds 350. I have the frame pads - what size bolts do I need ?
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Old July 17th, 2018, 06:26 PM
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I’m guessing the people asking these questions are under 30 years old, long before the days when all you needed to work on these cars is a 7/16”, 1/2”, 9/16”, and 5/8” wrenches and sockets. That would cover probably 90% of the hardware on old iron! 😎.

To answef your question, once again 3/8x16 thread, probably 1 to 1 1/4 long.
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Old July 18th, 2018, 06:57 AM
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You forgot the phillips screwdriver :-) Thank you for the reply. Frame pads are in and its looking like an Oldsmobile again. Sorry for hijacking the thread. I simply couldn't think of a better subject line to ask my question. Oh ya. 1" is the perfect length.
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