I'm going to assume it's the header flanges and not the heads but my basset headers do not fully seal up against the heads. I feel the exhaust coming out and also when i pulled my headers to do some maintenance i could see where the exhaust was escaping. I was wondering if this was common and if so what can be done to correct it. Can i have the headers surfaced? Should i double up gaskets?
~Shaun
First check the lower edge of the flanges looking for bright spots/scratches. If you use head studs the header flanges may be hitting the tops of the studs and/or nuts or bolt heads. Just about every BBC header I've installed had some type of interference and had to be ground away to clear.........MP
I'm using head studs, i already had to grind away on the flange a little bit but clearance is good... besides it looks like i'm leaking mostly out the top. Also it's not a small little area, when looking at the gasket i can see the burnt area is about 1/2" wide on some ports... These headers are about 15+ years old so they have had some abuse.. I havnt tried putting a straight edge on them yet, will tomorrow.
This is an old car trick, not sure if its applicable on boat headers: If a straight edge reveals they are warped, take a sawzall and cut most of the way through the flanges on both sides of the center two tubes. You can start from the bottom or the top, doesn't matter. Try not to cut all the way through so the integrity of the headers is not compromised. This allows the flange to flex at two spots and conform with your heads better and make for a tighter seal. Not sure if this makes sense in words, maybe somebody has a photo where they've done this. Again, never seen this on a boat but plenty of times in cars, especially when cheap headers (aka, thin/warped flanges) are used-Aluminum Squirt
Another thing to check is make sure the gasket is covering the flanges completely. Lay the gasket over the flange with several bolts in the holes and look to see if they're covering everything correctly. I don't know if the Bassets have a welded bead around the header opening, but if so, sometimes the gasket isn't covering this corectly. (If they don't have the welded bead, you're a little out of luck and Squirt's idea above will help) I always buy the small round port gaskets and use a die grinder to open them up to the tube dia. for a perfect fit.
In a pinch, I've used copper silicone. The gasket blew out and I didn't have a spare. Was surprised it worked. Don't know how long it would work in a lake boat.
I done the same thing (copper RTV) but used a good header style gasket to. Give both sides a coat, bolt everything up and let sit over night.
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