engine ground bolt size

[jk79ta]

Hope this is a simple question. What size bolt do you need to connect the ground strap from the firewall to the back of the engine? I've tried 3/8" x 16 and 3/8 x 24. Neither one will go in very far. Maybe the holes are just gummed up with crud or something but a don't want to screw up the threads.
Thanks,

Joe

[5th T/A]

I am not sure I understand your question.

If you are talking about the bolt that connects the transmission bell housing to the block, it is 3/8" by 16. The taped area into the block is probably an inch deep or less. This would be the same thread size as you find on the front or back of the cylinder heads where accessories mount.

The other end of the cable that goes to the floorboards is a sheet metal screw and doesn't need to be very long. If you stripped it out, just go one size up.

[pancho400cid]

I assume you're asking about the bolt that connects the thin braided ground strap between the rear of the passenger side cylinder head to the firewall.

I just checked the 400 engine I pulled out of my 78 Trans Am.  That bolt (definitely original in my case) is 3/8-16 thread and is 1/2" long (just the threads, not counting the bolt head), so it's a short bolt.  The wrench size is 9/16" - standard for a 3/8 bolt.

That said, I have definitely had engines where that same hole was packed with crud, so chasing with a tap etc. wouldn't be a bad idea.

...

[jk79ta]

Thanks guys. Thought it was 3/8x16, but didn't want to screw it up back there. Yes, it's the thin strap from the passenger side back of the block to the firewall. I just put a few washers on the bolt so I could get it snugged down. I think that will be adequate for now.
Thanks again.