As seen in Speedboat Magazine’s
May 2024 Issue.

TRY COPPER

Dear Bob:
I have a Formula 382 FasTech with a pair of Mercury 500 EFI engines. I have a
problem with the exhaust flange gasket leaking and blowing out on one of the
engines. The starboard rear cylinder keeps leaking. What are the best gaskets
to use? Thanks,

Randy Wallace
St. Clair, MI

SCE copper head gasket.

If you are continuing to have a problem with the header flange gasket blowing out, there is possibly a cause that needs to be addressed. It is likely that your header exhaust flange is warped, and less pressure is being applied to the gasket on the one port. You may be able to re-surface the mating surface which can be done with a large sanding belt. It is important that the surface of all of the ports are on the same plane which can be checked with a 3-foot straight edge. Once the exhaust manifold is installed, it should be retorqued after the engine has been run.

1. Header flange.
2. Header with copper gasket.
3. Header bolt hole not tapped deep enough.

Most of the engines that we build have CMI headers on them. In the past, we have experienced some problems with the gaskets blowing out. Usually the cause is that the header bolts loosen. Periodically tightening the bolts normally solves the problem. In some cases, we have discovered that the 3/8-16 bolt holes in the cylinder head castings are not tapped deep enough which prevents the bolt from being properly tightened before it bottoms out. This is not usually the case with the stock iron heads but more common
with after-market aluminum heads. If you suspect this might be the problem, you can use a bottom tap to make sure the threads in the head casting are deep enough.

When installing the CMI E-Tops like yours—or any of the headers with the similar primary port diameter of approximately 2 inches—we switched to solid copper header gaskets many years ago. This change has nearly eliminated the problem. With the solid copper header gasket, even if the header bolts loosen, the gasket survives, and the exhaust leak can be fixed by simply tightening the header bolts.

SCE Gasket Company makes solid copper gaskets for just about every application. They do have a solid copper exhaust header gasket for your engine. We keep them in stock, and they are also available from various performance parts sellers. The part number for the 2″ round port header gasket is 4313.

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