Intake manifold leak?

[Guest sintid58]

On my 55 Buick Special.

I put on a new right side exhaust manifold, had the intake off and inspected it, replaced the clean out plate and seal on the underside of the intake and started the car again Friday. It starts and runs great, very smooth not like it should be with an intake leak but I still have noise coming from the intake manifold. Sound like an exhaust leak but I can not see anything wrong with the manifold. So what am I missing.

[Bhigdog]

Stick a piece of plastic tubing in your ear and move the other end around the suspected area. you will be able to isolate the source of the noise very closely. Maybe now that your car is so quiet you can hear an exhaust leak you didn't know you had.........Bob

Edited January 30, 2010 by Bhigdog (see edit history)

[Guest sintid58]

I just hate exhaust or intake leaks, they sound terrible and dont do anything for the performance of a car. That said, I do like the sound of a V8 with a good solid exhaust system and glass packs on it. I would also like to know if there is a way to free up a frozen cross over valve on the left manifold. I think that may be froze closed and pushing more exhaust across than needed.

[Bhigdog]

soak it with Kroil, PB, Kerosene, whatever and tap the shaft from side to side. Sometimes it's easy, sometimes it needs to be removed to work on with a torch, sometimes it takes major surgery, and sometimes it's easier to just find a good one............Bob

[JohnD1956]

Did you put gaskets between the engine and the exhaust manifold?

[Smartin]

Pull the exhaust manifold back off and have a machine shop grind it flat. Reinstall with no gasket. I use a light coat of high temp RTV to fill imperfections. Never had a leak.

That said, you could have an exhaust leak in the crossover in the intake. There is the large plug on the underside of the intake that can rust out (but from your description, it sounds like you replaced that while it was out?) And there is also the exhaust passage that is routed under the carb itself...which is the reasoning for the steel plate under the carb...to keep the exhaust gas from coming in contact with the carb base. Check all of these areas.

[Guest sintid58]

I took the exhaust manifold to my machine shop before I put it on and had it machined flat and also magnafluxed for cracks. I have had bad luck using gaskets between the head and manifold so don't like to use them unless needed. When I start the car cold I can hear the leak and feeling around the exhaust manifold and listening that doesn't seem like the problem. I am pretty sure this is a intake manifold issue. I did replace the metal plate on the under side of that along with getting a new gasket from Old Tank (thanks again). I used metal gaskets on the intake manifold. My thoughts are that I need to have the intake manifold machined, there is a hairline crack in the intake, or maybe on of the heads is cracked where the exhaust passages pass through. I am just looking for something I may over looked and the more minds on the problem the better. Thanks

[Mark Shaw]

Spray WD-40 around the intake manifold with the car idling. It will speed up when you spray the intake leak.

and if you really want to find it use some starter fluid!

Edited February 8, 2010 by BUICK RACER (see edit history)