Flexplate bolt question

OK, finally got my old 91 4.0 out and just about everything stripped to go on the new engine and the flexplate bolts are giving me a fit.

Tried my 3/4 inch wrench - and it seems a little too loose, slipped off on me, and I called it a night.. .

I though it was SAE. . . Anyone know if it's a 19mm ?

Yeah I know, just check. . . but I've only got 1 19mm socket, with the side blown out. . .so before I run out in the morning tool shopping. . .

They're inch bolts (1/2"-20x1/2",) and I seem to recall using a six-point 3/4" socket on mine.

If you want to replace them, ARP has a kit for Pontiac that works. I don't recall the part number, but I know it's a kit for Pontiac flexplates, and it has six correct bolts - I've used it to replace bolts before.

For "critical" bolts like this, there's no reason to use a trashed wrench to turn them. Take a bolt with you to make sure, but get a nice snug fit (it should turn out to be 3/4", but 3/4" and 19mm are close enough to the same size that they get swapped out a lot. 9/16" & 14mm, 7/16" & 11mm, and 5/16" & 8mm are all "pairs" as well - knowing that comes in handy sometimes...)

5-90

I was thinking mine were 18mm. Not sure about it, but i just put my engine in less than a month ago. The transmission is foriegn, so metrics are likely, and 18mm is a common automotive size.

Jaredatriot:

OK, 5-90 would know better than me. Listen to him.

Yeah - the transmission's foreign, but the engine ain't. Since the flexplate bolts to the engine, that's the general idea.

What still gets me is the Mitsubishi starter bolting to a French, Japanese, or American gearbox and an American engine, having two bolts - one is 3/8"-16, the other is M10x1.5. WTF?

5-90

Nope not an 18mm - too small - I'd tried that. . . 18mm seems to be typically the biggest size in a metric set.

This block had a rebuild on it at some point, and alot of bolts swapped out and a few just left out... The waterpump was on with a 12mm and a 13mm rather than 1/2" that should have been there - I've been putting the correct bolts into the new block. Seems like if it threads into the block, it should be SAE. . . Not as random as I thought when I started on this project

I said "wrench" but yeah, my 6-point socket slipped off too. The 3/4 just ain't snug enough - I can rattle it back and forth. Off to the store for a 19mm. .

5-90 said:

Take a bolt with you to make sure... 5-90

Click to expand...

If I had one of them out, that would be easy. . . ROFL thinking about dragging the block into the store by the hoist chain. . . But, since it IS sitting in my utility trailer, it's not that bad an idea. . .

5-90, Thanks for the response as usual

You know, if I came into my hardware store with an engine on a cart, they probably wouldn't think anything of it... I've gone in a few times carrying a Briggs!

I'd thought you'd managed to get them out, and were having trouble getting them in. I'm fairly sure they're 3/4" heads, but there's usually some heavy thread-locking going on (or there at least should be.) Try this...

If you have a "pencil" torch, use it to heat up the bolt heat at the very centre. This will serve to break up any factory threadlocker that may be at issue (the flywheel/flexplate bolts are one of the few places to consistently get threadlocker from the factory.) This will likely result in a significantly weaker bolt - so do this if you have replacements handy. (ARP 200-2904 will work for replacements, and is just the right kit for the AW4 flexplate.)

It is also possible to take a centre punch and fetch the bolt a good whack (use a small hammer - 5# or less - and a short handle) in the dead centre of the head. This also helps to break up threadlocker, and is a useful little thing to have in your bag of tricks anyhow. You can do this after the torch work as well.

I've also found it handy from time to time to actually try to tighten the bolt 1/6-1/2 turn before loosening. It's often easier to turn it forward, and it sort of gives you a "running start" when you go to loosen the bolt next.

In any case, I'd definitely replace the bolts - but I'll do that any time I can anyhow (those bolts really are a pain to get to when you just have that to do...)

5-90