I bought this 1970 model 292 and would like to know the purpose of the bolts in the head above the exhaust manifold. I have circled one of them on attached pic.
Yep- - - -that head once had a piece of tubing with a gland nut on it, and a one way check valve to pulse air into the manifold like an afterburner. They burned out pretty quickly and the head usually got threaded for a pipe plug. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
On the Chevrolet V8's, the exhaust manifold was the item that was ported, threaded, and the point of Air Injection Reaction. That may be a California Head, I don't know when the "49 states" engines were built with A.I.R. but 1970 seems a little early for it.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
The original threads in the port were machine thread, unlike pipe thread which is a tapered thread. The A.I.R. port is in the exhaust passage downstream of the combustion chamber, even if the bolt/thread leaks a little, it is not leaking combustion or water or oil. If you get the engine running and there are no major exhaust leaks at the bolts, I would call it good.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
It only takes a few minutes to run a pipe tap into those holes and do a permanent fix that doesn't leak. I don't remember if the proper size is 1/4 NPT or 3/8 NPT at the moment. No drilling is required- - - -just chase the existing threads with a tapered tap. This can even be done with the head on the engine- - - -any chips that fall into the exhaust port just get blown away from the port into the exhaust pipe. I use Allen socket pipe plugs to fill the holes. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Nope- - - -I don't think anyone makes pipe tape that can stand exhaust temps that can approach 2000 degrees F. on a long uphill pull! I've seen temps that high on a dyno run with heat sensors in the exhaust ports. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
If those bolts have been in there since the '70's, they probably have enough carbon/rust in the threads to seal them. I would just run it with whatever is in the ports and decide if it's worth messing with, if it ain't broke, don't fix it.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Just about any thing threaded in the holes will work one of the easy ones is you Cut the fittings off the rail pinch the end closed and weld or braze it closed One of the few smog things that didn’t hurt performance much. Those are just part of life out here, the preferd way is to use a plug that has an allen head so it doesn’t show as much
I appreciate all your feedback. I'm taking the advice of 78buckshot: don't mess with it if it is not a problem.
But if it is a problem, how hard is it to pipe thread per Hotrod above, and install an Allen head plug. Can a rookie like me do it without screwing it up and making it worse?
Honestly I would leave it alone also, if they are plugged it’s all that matters You could cut the heads off the bolts just for looks. The way I mentioned is so it is reversible so could be made to pass emissions testing.
