Vintage Dirt Bike Q & A

The exhaust is leaking around where the pipe attaches to the manifold on my MT250. When I installed it, it didn't feel like it went on tight. I've tried tapping it on with a deadblow hammer to no avail. Is there some trick to getting a tight fit?

I've got another kind of leak as well. I noticed oil drips from the exhaust. I sandblasted the exhaust and repainted it. Looked good with no apparent holes. Turns out there are two tiny pinholes that I didn't see. They only leak when the exhaust is hot.

There is supposed to be a ring to seal the pipe. Before I fixed mine, it made a greasy buildup on the jug and frame below the pipe. I also picked up almost 5mpg when I sealed that, and lost the greasy goop on the exhaust outlet as well.

The ring is there, just cant seem to get the pipe to seal over it.

There's actually three rings (see diagram). The best way to get a good seal is to pull it apart, clean everything and replace at least the ring gasket (item 7), then reassemble with hi-temp compound on everything and strong springs (if they pop right on, they're too weak). The MT I worked on had the tapered sealing ring (item 5) carbon-welded to the pipe flange crooked, so the new ring gasket just squashed up on one side and leaked like crazy on the other. The piston-ring thing (13) seems to be mainly for mechanical centering, it sure doesn't seal worth a damn.

You could also try just compounding it, but that didn't work too well for me. JB Weld should seal any leaks; I used it on my MR's head pipe and it worked great.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

That explains it. Thanks Ray!

What do parts 5 and 7 look like? Is 5 a material type gasket similar to plumbers tape? Is number 7 a copper ring? Any ideas where to find these still, or something that will substitute?

Part 5 is a machined steel collar- I think its function is to compress part 7 (asbestos-looking ring gasket) onto the end of the exhaust manifold.

CMSNL has both of them, I believe:

http://www.cmsnl.com/products/collarex- ... 325358303/

http://www.cmsnl.com/products/gasket-ex ... 352358000/

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric