Leaking exhaust gasket

Das Chicken

Member
Mar 22, 2012
41
0
6
Georgia
My 48/49cc two stroke HT engine's exhaust gasket is leaking. The whole front end of the engine is saturated in oil (not the top though). Whats rust? It even decided that it would be a good idea to spray scalding oil on my leg (felt like a bee sting). I am using a self port-matched METAL gasket. any ideas on how to seal it? Is there some sort of liquid gasket material that won't melt off; and still allow me to remove the exhaust pipe somewhat easily? This should be put up as a sticky if it gives conclusive results.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
241
63
up north now
Remove the pipe, and studs and use a file to dress the mating surfaces, both in the pipe sn[[and the cylinder, then use a new gasket torqued to the proper amount
 

dragray

New Member
Mar 10, 2012
278
2
0
Indiana
if you use the aluminum exhaust gasket from sbp, you shouldn't have to file the exhaust port flat as suggested. (the mating surfaces).
by the way, good luck getting those exhaust studs out without breaking one, or destroying the threads.
the soft aluminum exhaust gasket is malleable and it will conform to the irregularities on the port and on the exhaust flange.
the aluminum gaskets are re-useable as well.
I personally put a LIGHT FILM of high temp silicone on each side of the gasket, and install it. I just tighten the nuts tight by hand, i don't torque them.(hand tight to one guy may be finger tight to another guy...i just know when to stop tightening)
I've done this several times on several different engines, and i haven't had a leak yet.
 
Last edited:

killercanuck

New Member
Dec 17, 2009
1,748
4
0
44
Wallaceburg ON
Dudes! For one, never file a port surface, unless you have a really long file and a good eye. You'll end up making it worse. And two, the two studs come out easily when you know what you're doing.

2-double nut the stud with two nuts and lock them together with two wrenches(or vicegrips or whatever). Unscrew on the inner nut and it'll come out. Then,

1-using something flat(flat-steel, wood), wrap some sandpaper around it and sand with that. That will give you a much flatter surface than taking a file to it.

4-dragray had a good point, some copper rtv on the surfaces will ensure sealage, even for your metal gasket.

3-if you have an old leather boot, cut out a chunk of that to use for a gasket, bullet casings or hole punches can be used for the stud holes. Then clamp it on good once, and take it off. Now you have a perfect imprint of your ports to get out the exacto knife and have at it.

5-you can still rtv the leather to make sure the seal is good.

Don't forget to sand your exhaust flange with your flat surface, that'll help flattening both surfaces. While you have it off, is a good time to port match the flange the best you can, for better performance.

gl.
 
Last edited:

2door

Moderator
Staff member
Sep 15, 2008
16,337
165
63
Littleton, Colorado
Remove the exhaust flange from the cylinder. Clean the old gasket off and use some good solvent on the gasket mating surface. Now take a Magic Marker and 'paint' the gasket surface of the flange with it. Next using a known flat surface, glass works best, rub the 'painted' area of the exhaust flange over a sheet of sandpaper that you laid on the glass.
What you want is a uniform surface. After a few strokes across the sandpaper you'll easily see where the high and low spots are that need to be eliminated before you can expect to get a good, leakproof seal at the exhaust flange.
Glue, gasket sealer, metallic gaskets, all are bandaids for a poorly prepared gasket sealing surface. Get the flange and the mating surface of the cylinder flush and then use a gasket material intended for exhaust, properly torque the fasteners and you'll never have to worry about leaks again.
Tom
 

Das Chicken

Member
Mar 22, 2012
41
0
6
Georgia
if you use the aluminum exhaust gasket from sbp, you shouldn't have to file the exhaust port flat as suggested. (the mating surfaces)
Well, i dremmel'd the gasket (and muffler), to match the cylinder ports. Some of the material likely curved and is causing the leak. I'll file it down smooth sometime soon, i've got the top end in pieces, and i have a final today and tomorrow.
 

maurtis

New Member
Dec 14, 2011
707
0
0
Kyle, TX
I tried one of those aluminum exhaust gaskets when I first installed my motor and it leaked a little, so port matched the stock "pressed dog food" gasket and used that instead, and so far no issues. I did not use any gasket sealant, though, so I am sure that would have helped.

If/when I blow out the stocker, I will give the Al gasket another chance... good luck!

***edit***
It makes me a little sad that I just spent any time at all finding out which pony your avatar is... uh, yeah... sigh.
 
Last edited:

Das Chicken

Member
Mar 22, 2012
41
0
6
Georgia
I tried one of those aluminum exhaust gaskets when I first installed my motor and it leaked a little, so port matched the stock "pressed dog food" gasket and used that instead, and so far no issues. I did not use any gasket sealant, though, so I am sure that would have helped.

If/when I blow out the stocker, I will give the Al gasket another chance... good luck!

***edit***
It makes me a little sad that I just spent any time at all finding out which pony your avatar is... uh, yeah... sigh.
The reason i got the aluminum gasket in the first place was that both of my paper gaskets disintegrated when the pipe was removed. Not to mention that any port-matching would be impossible without destroying the gasket.
It makes me a little sad that I just spent any time at all finding out which pony your avatar is... uh, yeah... sigh.
Don't be too hard on yourself, my avatar is a rendering of twi's mental breakdown. My big brother who the one who made it in the first place. Scootaloo is best chicken!...err..I mean filly.