My 75 has a small annoying exhaust leak at the front of the engine. I investigated and found there is no gasket at the heads, is this the norm? Can I install gaskets if they are made. Also, a mechanic said its probably the donut but I dont see a listing for a exhaust donut on the passanger side in Ecklers. My exhaust is all stock.
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Re: exhaust donut
Yes you can change the exhaust donuts on your 75. This exhaust gasket is the same thick round gasket for each side. It can be purchased at any automotive store. There is a gasket for the right /passenger side that is not used on the left, it is a thin flat gasket that goes between the heat riser valve and the cast iron exhaust manifold. You should loosen the exhaust clamp at the middle of the car to facilitate change out of the exhaust gasket. -
Re: exhaust donut
THANKS JimComment
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Re: exhaust donut
There should be no gasket between the head and exhaust manifold. Unless one or more of the exhaust manifold bolts into the head has failed there is no need for one. Frequently on rebuilds folks (usually engine shop) like to install such gaskets, but if the exhaust manifolds are intact (that is ears not broken off) and bolts not broken, and fasteners are properly torqued there should be no need of them.
When the engine is run with failed exhaust manifold fasteners or broken ears then warpage can occur and sometimes even the addition of gaskets are then not sufficient to stem the leak. More drastic measures are then needed, but there is no need to explore them here if that is not your problem.
There are two styles of exhaust manifold to exhaust pipe (doughnut) gasket available. There is a fiber type that used to be made partly of asbestos and a cast iron doughnut. My 1970 originally came with the fiber type. You might want to look at your car before you go to the parts store. I think the cast iron type are used on trucks, but with the increase of exhaust heat used with catalatic converters they might have changed to the iron type.
Terry
TerryComment
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Re: exhaust donut
Eddie-----
As Terry mentioned, no small block Corvette V-8 was ever originally fitted with a gasket between the heads and exhaust manifolds. Many aftermarket upper end gasket sets do come with composition, "waffle pattern" gaskets which can be used as gaskets for the above application. Genereally, if these gaskets are required it means that the exhaust manifolds are warped or otherwise distorted. In that case, since you have to remove the manifolds anyway to install the gaskets. I recommend taking the manifolds down to your local machine shop to have them surfaced to produce a perfectly flat and true surface. That's the way to correct leaks at the exhaust manifold to cylinder head interface. I don't like "band-aid" type fixes.
Your exhaust leak is very likely your exhaust "donut" gasket. This is a common source of exhaust leaks. Like Terry said, your engine probably used an organic donut which was partially composed of asbestos or other replacement fiber. I don't ever recommend these donut gaskets. Use the sintered iron type that Terry mentioned if you can get one. Otherwise, the original donut gasket is still available under GM #3731062 for $2.30 each. You could try just tightening the 3 exhaust flange stud nuts on this side, but, usually, if they are loose, you will need to replace the donut anyway.
Be advised, though, that your 75 uses this donut gasket ONLY on the left(driver) side. The right(passenger) side uses NO GASKET or Donut. Your car uses a vacuum controlled heat riser valve which is specially configured to provide all of the sealing. No donut or flat gasket is used on this application. If this is the side where your leak is occurring, AND YOU HAVE CONFIRMED THAT THE 3 EXHAUST FLANGE STUD NUTS ARE PROPERLY TIGHTENED, you may have to replace the heat riser valve assembly or the exhaust pipe to cure the problem.In Appreciation of John HinckleyComment
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Re: exhaust donut
Joe,
I purchased a set of the iron doughnuts from Chevrolet. Not sure the application, thus my speculation about truck in the earlier post. I can look in the garage for numbers.
Terry
TerryComment
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Re: exhaust donut
Terry-----
I think that the sintered iron donuts have more-or-less replaced the earlier organic type. Perhaps this occured as part of the effort to rid the country of the "scourge" of asbestos. In any event, most of the GM gasket kits like top engine kits and intake manifold gasket kits now come with the sintered metal type donuts. So, I usually end up with a lot more of these around than I need, but I still don't know the part number since they're part of the kits. I would be interested in finding out what part numbers might be on the iron donuts that you have if you have them in their individual GM packages. No rush, though.In Appreciation of John HinckleyComment
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Re: exhaust donut
Joe, I just replaced the exhaust system on my '78 L-48 and have an annoying leak on the passenger side. There was a gasket between the heat riser and manifold when I removed the old exhaust. I also found the original heat riser had a broken weld at the internal flapper, causing it to vibrate noisily. The local Chevy dealer wanted $207 for a replacement heat riser valve, so I settled on a $40 reproduction.
I'm thinking that the heat riser valve is warped, causing my exhaust leak. Is it possible to have this machined flat along with checking the exhaust manifold, or should I bite the bullet and spring for an original valve, or try just a flat gasket and see if this fixes it?
Appreciate any suggestions.
Greg.Comment
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Re: exhaust donut
Try the gasket if you don't mind the work of the R & R.
Terry
TerryComment
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