Vintage Dirt Bike Q & A

Exhaust pipe collar
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Author:  Michaels [ Mon May 28, 2018 1:18 pm ]
Post subject:  Exhaust pipe collar


I'm re-installing the stock exhaust pipe for a 1975 MT250. I bought a new OEM gasket (GASKET, EX. PIPE 18352-358-000) and NOS collar (COLLAR, EX. PIPE 18325-358-303). ... 5-358-303/

The NOS collar is tapered and I want to be positive which side faces into the pipe and which side faces the gasket (& engine). I can't find any information on this anywhere. Has anybody installed this same piece?

A or B?

exhaust collar A1.jpg
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exhaust collar A2.jpg
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exhaust collar B1.jpg
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exhaust collar B2.jpg
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Author:  rayivers [ Mon May 28, 2018 6:18 pm ]
Post subject:  Re: Exhaust pipe collar

The exhaust ring fits into the pipe inlet flange as shown in your picture 'A1', with the chamfer facing out. The end of the exhaust manifold has a matching chamfer, and the white ring gasket will end up sandwiched between these two chamfers. The MR175 has a very similar setup, except the ring & gasket are combined into a single chamfered ring.

Here's how I've installed these setups, with no leakage yet - it's important to have the pipe ready to go on, with all brackets on, nuts handy, etc:

1) Clean everything well, especially the pipe flange and manifold 'piston ring' groove
2) Apply hi-temp sealant to the inner pipe flange and metal ring, and insert it till it bottoms (chamfer out)
3) If the manifold is off, use the same sealant & Honda gasket to install it on the engine
4) Install the manifold 'piston ring' (not shown in your photos) into the manifold groove after coating it and the groove
5) Coat the manifold spigot and white ring gasket, then install the gasket on the manifold end
6) Coat the inside of the pipe flange, then carefully slide it straight onto the manifold
7) While keeping the pipe in place, put on the rear bracket nut loosely to hold up the far pipe end
8 ) Push the pipe onto the manifold firmly while installing both springs
9) While still keeping most of the pipe weight off the manifold end, install & tighten all mounts

You might want to try a dry run first, as the manifold / piston ring / gasket can be a little tricky to force into the pipe flange,
and it can be hard to tell if the pipe is bottomed fully onto the manifold. These pipes are heavy and have significant backpressure,
so they chafe and eventually start leaking unless sealant is used everywhere. With sealant, they neither leak nor chafe.


Author:  Michaels [ Mon May 28, 2018 8:49 pm ]
Post subject:  Re: Exhaust pipe collar


Thank you very much. This is extremely helpful.

I have not taken off the current pipe, which the previous owner installed. The manifold is already there, connecting the current pipe. When I remove that pipe, will I need to replace the 'piston ring' also? I only got new parts from the muffler side, # 5 & 7.

Do I also need to replace, on the manifold side, #13? Is that the piston ring you refer to? I don't want to make the switch until I have all the parts I need.

When you say coat the ring and manifold groove, you are still referring to the high temp sealant?

muffler diagram.png
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cylinder diagram.png
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Author:  rayivers [ Tue May 29, 2018 6:06 am ]
Post subject:  Re: Exhaust pipe collar

I don't think you'll need to replace the #13 piston ring unless it's missing. Also, if the manifold seems clear inside I wouldn't remove it, so you shouldn't need the #14 manifold gasket either. FWIW, I've replaced the piston ring with a hi-temp O-ring on my MR175 manifold; it degrades with time, but in conjunction with the sealant continues to seal fine.

Yes, all the 'coating' I mentioned was with hi-temp sealant (usually silicone based). I used to assemble the pipes dry, and they either leaked immediately or within a few months of use. It also makes for easier disassembly later, as the sealant is much softer than baked-on carbon.


Author:  Michaels [ Tue May 29, 2018 9:12 am ]
Post subject:  Re: Exhaust pipe collar

Thank you, Ray.

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