I don't think that is the problem but should be on the list of things to check! I do think the proper bolts should be used there.If you use bolts that have the thread all the way up then it could take less to shear!:cool:

I am pulling the flywheel housng off a new engine tommorrow. I will try and check the clearance for you. Checking it is not a problem, remembering is the issue! My memory is toast.

Here's an update - Pulled the flywheel housing and sure enough, the coupler bolt heads were hitting the housing. Put hex head bolts in and everything is great. There is probably less than 3/16" clearance in there from the head of the bolt to the housing. Live and learn, but it always seems to be the hard way.

:) Thanks for the update :)

So how does she run???

It sounds great but it's still in my driveway! Hope to splash it this weekend.

Let us know how it works. Is a 421 a 400 with a stroker crank??

That's made with a 3.875 stroke crank. I think it's similiar to the new cranks beings used in the GM 383HT crate motors. You use it with a 400 block or aftermarket (Merlin Motown, etc.).

A close friend runs one of these monsters on the jug... Motown block, 421 CID, all roller, 9.0's @ 150+/- in a 3000 lbs. (with driver) Nova. I like it!

It's a DART Little M block with a SCAT steel 3.875 crank. Last year it was a 415, this year it's 030 over so a 421. Had it out on Saturday and it ran real good but still needs a little tweaking. The weather's been so great here, I just want to enjoy it for a while. I'm tired of wrenching.