Flex plate crank bolt craziness?

Chad Hilburn · Oct 20, 2025

Hey, guys, I'm running into a weird situation. Most of the flex plate bolts that bolt, the flex plate to the crank on a mopar big block are supposed to be 7/16 thread. I've got a 383 that is a early 68 engine. It may even have a 67 casting date. But i'm telling you, the seven sixteenths bolt won't fit into the crank holes. There's got to be a smaller size? Anyone run into this?

ckessel · Oct 20, 2025

Never. Doesn't mean it never happened though. Run a tap through it?

33 IMP · Oct 20, 2025

Have you got the right thread? 7/16-20? (I do not mean to insult, just asking. You seem to have an unusual problem.)
Are you sure you don't have Metric bolts? Or 1/2 inch.?

There has to be a reason.

Chad Hilburn · Oct 20, 2025

ckessel said:
Never. Doesn't mean it never happened though. Run a tap through it?

Hey there, no, they are actually smaller. Ran a fine thread 3/8 thru there and fits perfect. This is the second time I ran into this. Just recently we got a 7/16-20 set of arp bolts for his, and same thing. Too big. Had to go to next size down

Chad Hilburn · Oct 20, 2025

ckessel said:
Never. Doesn't mean it never happened though. Run a tap through it?

It literally appears to be a 3/8 thread. 2nd time ive seen this recently. 7/16 is way too big a bolt

Chad Hilburn · Oct 20, 2025

33 IMP said:
Have you got the right thread? 7/16-20? (I do not mean to insult, just asking. You seem to have an unusual problem.)
Are you sure you don't have Metric bolts? Or 1/2 inch.?

There has to be a reason.

I'll tell you what it literally is a smaller bolt, all six of them. I got what I think is a 3/8 fine thread holes

MWbirdLOVER70 · Oct 21, 2025

Ok then try it id say

Flex plate crank bolt craziness?

Chad Hilburn

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ckessel

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33 IMP

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Chad Hilburn

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Chad Hilburn

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Chad Hilburn

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MWbirdLOVER70

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