Exhaust Manifold Leak

[toneypenna]

Having a problem with an exhaust manifold leak.

455 bored 60 over with ceramic coated W Z exhaust Manifolds.

Manifold has been re surfaced and am using fel pro Gaskets.

Keeps blowing out the gasket at # 8 port . This has happened at least four times in 3000 miles since I built the engine. Usually after a 3hr run at highway speeds.
Last time I tried a double gasket -- same problem.

Don't think it would make any difference but engine is in a 53 Olds.

Any body have any ideas.

Thanks Jim

[2blu442]

Hello Jim
There was a recent thread discussing this and Joe said that these engines came from the factory with no gasket between the exhaust manifold and head. You can do a search and read through that thread. Since you've already surfaced the manifold I'd try it without gaskets.
John

[toneypenna]

John

Will try it.

Willing to try anything at this point, Next would be to change the heads.

Jim

[joe_padavano]

Let me clarify. While it is true that Olds did not use exhaust gaskets with factory manifolds, the use of gaskets should not be the cause of a gasket blowing out. When you take the manifold off, check both the manifold and the head with a straightedge.

[toneypenna]

Joe

Thanks for the reply.

I had the manifold surfaced and last time I blew a gasket i did check it with a straight edge, however, I did not check the head. I will do that this time.

I had another thought. I am using C heads that I had ported, could the porting if not done correctly have anything to do with it?

Jim

[joe_padavano]

Originally Posted by toneypenna

Joe

Thanks for the reply.

I had the manifold surfaced and last time I blew a gasket i did check it with a straight edge, however, I did not check the head. I will do that this time.

I had another thought. I am using C heads that I had ported, could the porting if not done correctly have anything to do with it?

Jim

Yes. Depending on where the porting was done. If there is insufficient material left to seal the manifold to the head, that could lead to leaks, particularly if there is some mismatch between the manifold and the head.

[72 cutlass455]

I need to replace or upgrade my exhaust manifolds also. My old mechanic in NY would not do them unless i had a set of good replacement manifolds he said that the metal tends to get brittle with age. Also what is the best way to take the bolts off when they have been on there forever.

[Texascarnut]

Originally Posted by 72 cutlass455

I need to replace or upgrade my exhaust manifolds also. My old mechanic in NY would not do them unless i had a set of good replacement manifolds he said that the metal tends to get brittle with age. Also what is the best way to take the bolts off when they have been on there forever.

Yup, factory cast iron exhaust manifolds will become as brittle/fragile as glass with time thanks to being subject to very high exhaust temperatures. Assuming the car is not a daily driver, the best thing to do is soak down the bolts or retaining nuts whichever more applicable with something like PB Blast several times over a two to three day period. It maybe necessary to elevate the engine to get to the ones on the bottom. Just remember the last thing you want is a twisted off bolt or stud. 500 gorilla power on the end of a wrench is not a good thing. Patience and reasonable handling required. Twisted off bolts or studs are no stinking fun at all!

If you have a set of replacements it might be best to just let a shop tackle the job. It isn't the easiest thing to deal with under the shade tree or in a driveway.

[70Post]

Also--Try tightening everything but the center bolt first....once tight go back and snug up the top center bolt. Don't crank the heck out of the top center bolt just get it nice and snug.

If you have access to a superflat surface...I mean very flat....you can put down some sticky backed sandpaper and slide the machined surface of the exhaust manifold around on that a little to double check the surfacing job.
Once you slightly sand it a little you will be able to see a pattern from the sandpaper and if it's not cutting uniformly that may show you where exactly the manifold is not mating up.

Also...once you initially remove the manifold and gasket check the side of the manifold and gasket that faces the exhaust ports in the head...look for "overhang" or areas where the manifold and/or gasket is hanging down into the exhaust stream. This area would be dark or "burned" where the exhaust stream is hitting it.