Why Would Exhaust Manifold Gasket Blow

awca12a

My '29 Essex kept stalling every time I took my foot off the gas and I

had to resort to rolling starts to make it home because the battery was

finally exhausted from all the restarts. Once in the garage, I found

black smoke puffing from under the exhaust manifold next to both of the

long exhaust manifold studs. (Part #BM 63553) I'm probably getting the

wording wrong but I believe it is directly under the carb riser to

exhaust manifold and bounded by the long studs.



My question is before I simply take off the carb and exhaust manifold

to replace the gasket, what would cause exhaust to blow-by this area at

idle (and running) when it was working like a top all morning?



I'm still new to motor teardown so perhaps I'm missing somthing basic

like ????



THanks



David Weinstein

'29 Essex Roadster

'72 Corvette Cvt

Unknown

As far as exhaust maifold gasket failure goes, age and improper installation are causes, but heat is the true enemy.

[Deleted User]

It sounds like you have an obstructed exhaust system. Has the car been sitting, possible rat nest. Also, check to see if your the flapper in the manifold is stuck closed.



Harry

Unknown

Also check to see if the gasket surface of the manifold is true and flat.

[Deleted User]

Dave, does it seem like it doesn't have any power? I'm wondering if it was running fine before this started happening or was this the first time you had it out. Does this car have a heat exchange butterfly flap to push hot exhaust gasses up to the intake until the car is warmed up. Maybe the it's stuck closed and is causing the manifold to get too hot. It could also cause the gas to boil in the carb and vapor lock.



Harry

ESSX28-1

Check your that both your vacuum tank & your carb float are working as they should.

Unknown

Did it ever back-fire? If so, that would be an above-average amount of exhaust pressure, perhaps above the design pressure of the gasket, and potentially leading to the premature failure. When you replace it be sure to torque to specs and recheck the torque twice a year.