Exhaust manifold question.

[BLAZEN70]

About a year ago I replaced the RH stock ramhorn because it developed a crack and now I have to replace the LH side which bulged out a little and cracked. I know this is caused from excessive heat but, I don't know why. I don't think there are any blockages in the pipes. A friend of mine suggested the engine could be running too rich. Could this be the cause?? Any help would be appreciated.

[jhow66]

If it is running too lean would cause this not too rich. Rich-cooler, lean--hotter.

[skid]

Where did it crack? I don't think heat alone would cause a crack. Must be stress some where, like having the exhaust pipe mis-aligned, and then tightening up the studs.

[JimKshortstep4x4]

Something to consider on your cracking problem. When the emissions controls were first introduced on cars, the timing was set more retarded and the cars had controls on the vacuum advance to keep it retarded under certain conditions. The end result was that the manifolds ran hot. This was done intensionally since the theory was with the manifolds hotter more gases would be burned.

A lot of manifolds were cooked and ended up cracking overtime.

Jim

[moodyholler]

My rh cracked and upon inspection I found 1/8 " slop in the throttle shafts of my original QJ. Needless to say it was running way lean. Now have a 1406 Edelbrock and runs much better. moodyholler

[BLAZEN70]

Originally posted by skid
Where did it crack? I don't think heat alone would cause a crack. Must be stress some where, like having the exhaust pipe mis-aligned, and then tightening up the studs.

On the RH side it was cracked right on the inside curve of the center dump. On the LH side the center dump is slightly bulged out with multible cracks.

Robert

[Paul72]

My LH maniford has the same bulge/crack, and my RH has a crack or two as well. Personally, I think it a factor of design/miles/time. Nothing lasts forever, and sometimes ya just gotta throw it out and replace it!

It gives you a good reason to put some headers on it

Paul

[bpmcgee]

Paul,

Although you have an interesting theory, I don't think many people would consider cast iron manifolds to be wear items!

There has to be some sort of stress that's causing these to crack. Extreme heat from running lean could be a contributing factor -- I saw my manifolds glow orange one time when I had my idle mixture set too lean

Brian

[Paul72]

No doubt that there are other forces that can cause cracks. I was only saying that 30 years of temperature fluctuations, along with the wall thickness inconsistencies, and uneven heat distribution, can also cause stress and possibly failure. My manifolds have been removed and replaced, which probably resulted in my condition, but who knows.