4-2-1 Exhaust Manifold Questions

[dsnyder]

Mine had bolts but they have vibrated out and now the car is obviously noisy. I want to put in studs. Anyone know what thread size/pitch will fit in? (I'm talking about the connection to the downpipe, not the head). This is the manifold with the six bolt holes in it.

Also, there was no gasket between the manifold and the downpipe. I made one out of gasket material but I read somewhere that this is a metal to metal joint with no gasket. Is that correct? Can I use hi-temp silicone to help it seal?

Thanks,

Dave

[Mathew26]

It is a metal to metal fitting, and the thread pitch should be 1.25

[So Cal Mark]

if the flange surfaces are flat, it will seal without a gasket. If the flanges are warped, no amount of high temp rtv will cure it for very long

[mbouse]

Dave, are you talking about the two hole gasket that fits between the exhaust manifold and the down pipe? there are only four studs at this joint, not six.

Matt may not have heard of them, but i generally keep a spare one hanging about because i have had those nuts come loose from the studs. i believe the size you are looking for in the fastener is a 8mm x 1.25 thread. and if we are talking the same fitting, stock was a stud not a bolt.

the problem occurs when you attempt to use el-cheapo fasteners (like i did). the expansion / contraction of the pipes tend to loosen these fasteners over time. most down pipes lost their unique stamped steel nut locks long ago. when the fasteners loosen, it tends to blow out the gasket...causing an obnoxious racket. good luck getting that fitting to seal noiselessly w/out the gasket. V.O.E. (voice of experience).

and, the gasket may no longer be sold by Matt's employer ( i could not find it in the VAS catalogue)... but others have them in stock... and on-line. should be about $4.25 plus shipping. search for 1973 exhaust manifold flange gasket.

[RJ80]

Dave, are you talking about the two hole gasket that fits between the exhaust manifold and the down pipe? there are only four studs at this joint, not six.

The FI version has six, I believe and was designed to fit without a gasket. If it's not flush, a machine shop could probably grind both so they mate properly.

[mbouse]

WHELL... there's the difference. which is why i went to such pains to identify the part i was speaking of.

[dsnyder]

OK I have secured the studs and some special nuts made for exhaust that are locknuts without meltable parts. I'll be trying to put them in tomorrow.

Thanks everyone!!!

Dave

[So Cal Mark]

the original nuts were brass. Be sure to use antiseize on your nuts (well, maybe the cars' nuts) or you may never get them off (the cars' nuts that is)