Thread Size of EGR on a 292 Head
 

I tried another forum and came up dry. I am hoping someone has this information. I am refreshing a head on a 292 and am going to plug the EGR ports. This is a later model head with the larger thread size. Does anyone know the thread size? It is definitely an oddball. I would like to run a tap through them as the threads look a little suspect.

My guess right now is a metric pipe thread M18-1.5 ????

Re: Thread Size of EGR on a 292 Head
 

I see the crowd was slow to respond. I guess you could check the pitch of the EGR with another known metric bolt. I'm assuming you still have the old EGR valve handy. If you're confidant enough with that fit then gently try a bolt of the right size.

Re: Thread Size of EGR on a 292 Head
 

Its been a long time but if I can remember it was an inverted flare nut. I used to take the old nuts & weld them shut.
George

Re: Thread Size of EGR on a 292 Head
 

Thanks guys.

Wrenchbender, I think your memory is correct. My best guess right now is it is a 3/4"-18 flare thread. I have not 100% confirmed this, but dimensions match up perfectly. This makes more sense in that the EGR pipes themselves were flared.

It definitely is NOT the metric fitting.

Re: Thread Size of EGR on a 292 Head
 

My latest 292 is a MY '68. So I don't have one. I looked it up on the illustration in Santucci's ''Chevy Inline Six Cyllinder Power Manual'' and found nothing. I have the first edition. Might be shown in the later editions. IDK.