Exhaust Manifold Leak

[MercuryMarc]

Any tips to how to seal the exhaust pipe flange to the exhaust manifold? I have repleaced the gasket (donut) twice and still have a small and annoying leak- I can't get it to seal right. It's a 78 head on a 69 250 block that I rebuilt last year. Thanks!

 

[wallaka]

Make sure the mating surfaces are smooth and flat (I used a Dremel and a shop light to see any gaps) and you have the correct donut for the manifolt. There were two outlet sizes, and either donut will work in either hole, though it won't seal well. Also the downpipe needs to be the correct diameter for the manifold. Again, either will work but not well.

 

[Redfalken]

Hi Marc,

I had some leaking where the manifold mounts to the head and didn't want to spend the $$ on getting the head surface milled. I had the manifold surface milled (it was warped) and put a small amount of Permatex Ultra Copper between the gasket and head, around each opening. It's supposed to be good to 700 degrees.

So far it's holding up well. You might try that as a last resort.

 

[MercuryMarc]

Thanks Kenny and Wallaka-
I got it to seal by loosening all the muffler ahd exhaust clamps, then mating the manifold port to the exhauast pipe with a new donut, then reattaching all the exhauast and muffletr hangers again.

 

[Anonymous]

I used a Dremel and a shop light to see any gaps

Yup. When I built the turbo set-up, I had to make sure the donut mounting was PERFECT.

I started with a sanding drum in a drill and cleaned all the rust off. I then gave it a coating from a black magic marker (poor-man's "machinist's blue")

and then carefully rotate the donut.

The high spots get worn off....that's where you know where to sand. Keep painting with the marker until it makes a clean ring all the way around.