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Exhaust Gasket

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Perko725/07/2019 06:52:44
320 forum posts
24 photos

Hi all, just wondering what people use for exhaust manifold gaskets on small I/C engines. Using a 25cc strimmer motor to drive a loco but needed to make a new exhaust system to fit inside body. Existing gasket too thin to give sufficient offset to new exhaust to clear other bits. Thinking about using a piece of 3mm aluminium with a smear of gasket cement on each face. Any thoughts? Exhaust connection is steel, held on with two M5 cap screws into existing exhaust mounting holes.

David George 125/07/2019 08:01:55
1197 forum posts
409 photos

Hi you can use copper for an exhaust gasket cut it out and then aneal it by heating it to bright cherry red and quench in water. It will work no problem.


Howard Lewis25/07/2019 12:04:59
3159 forum posts
2 photos

If the cylinder head is aluminium alloy, beware of using copper gaskets!

In the presence of any moisture, (as in storage ) which will probably produce an electrolyte, the Aluminium alloy will be corroded by the copper.

Gasket cements may not withstand the temperature when the engine is working hard.

This does happen! I have seen alloy, "water" cooled exhaust manifolds and gearbox oil coolers, on marine engines ruined by the use of copper gaskets.

It would be preferable to use a steel faced gasket, if the head is light alloy.

Copper between a steel spacer and the steel exhaust flange will be quite acceptable.

You might get away with using a copper gasket, with a steel shim between the Aluminium and the alloy head. In this way you remove the Copper/Aluminium electrolytic cell.


JasonB25/07/2019 13:08:02
17882 forum posts
1954 photos
1 articles

Silver solder a bit of 3mm steel to the existing exhaust flange to get the extension you want then use whatever gasket you would normally have done, it's one less joint to worry about.

mgnbuk25/07/2019 13:26:52
748 forum posts
60 photos

Standard "gasket" on two stroke trials bikes I have had was a smear of clear silicone sealant on the joints at assembly.

Nigel B

Perko725/07/2019 13:39:28
320 forum posts
24 photos

Thanks all. Copper is not an option at the moment as I don't have a suitable piece available, and anyway the cylinder is alloy so there could be a problem of galvanic corrosion. Gasket cement would be the type designed for exhaust systems (CRC Maniseal). The rest of the exhaust system is silver-soldered together so silver-soldering another piece of steel to the flange would run the risk of upsetting the existing joint of the flange to the pipe. I've thought of soft-soldering a piece of steel to the existing flange but I'm not sure whether this is practical with the heat of the exhaust possibly melting the solder thus potentially losing the seal.

I already have a piece of 3mm Aluminium made up to suit, so I'll give it a try and see how it works. If no good then I'll explore other options.

JasonB25/07/2019 14:46:44
17882 forum posts
1954 photos
1 articles

In that case just use a couple of layers of exhaust gasket with some jointing on all the faces to give the thickness you require. I have bought A4 size sheets of it from E-bay

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