Vintage Dirt Bike Q & A

Does anyone have (or know where I can find) an exhuast collar for a '74 MT250. Number 5 in the schematic. Most places say this part is now obsolete.

A fat hi-temp O-ring might work for now, until you find a collar; just big enough to stretch over the recessed tip of the exhaust manifold, and as thick as you could find while still being able to slide on the pipe. I've never had my buddy's MT250 pipe off so I don't know what the pipe flange's forward inside edge looks like; if it's a rough welded surface it might chew up the O-ring (or gasket) pretty quick without the collar as a buffer, but maybe you could smooth it down with a grinder or sandpaper if needed.

eBay item 380091970615 is the gasket; it's not what you asked about, but I included it in case you need one of these too.

My MR175 has a similar arrangement, but it only uses the 'piston ring' (on the manifold) and a single wire-mesh ring gasket, without the collar piece.

Ray

P.S. Just for grins, make double sure the collar isn't still in the pipe flange, covered by a thick layer of carbon. I pulled another buried ring gasket out of one of my MR pipes this morning, bringing the total to three so far.

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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

Ray,
Thanks for the reply. I did check the pipe flange this morning and there was no sign of the collar stuck or caked on. I am not sure my bike ever had the collar (like your MR175), after taking off the muffler assembly I noticed the "piston ring" was cracked and the whole gasket was missing. I found both the ring and gasket on the internet, but can't find the collar.
I may go with your O-ring idea, I was thinking some type of sealer to help reduce the contact area between the gasket and flange.

Some hi-temp sealer surely couldn't hurt. If the pipe slides onto the manifold far enough (without the collar) to allow the pipe to contact the manifold flange, it might work well to use another O-ring at that point too (mainly as a mechanical buffer, since a new piston ring probably won't allow much leakage). I did that on my '74 CR125 pipe and it helped a bit; it would have worked much better if the pipe was absolutely square to the manifold, but unfortunately it was at a slight angle and never sealed right.

On my MR, it seems like the ring gasket does most of the sealing duty (after it fills up with carbon, anyway), while the piston ring's job is to keep the pipe flange centered on the manifold and relatively stationary and also provide secondary sealing. I guess Honda wanted to keep the MT250 manifold short for some reason, and added the collar as a gasket spacer instead of shortening the pipe flange.

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