FMF silencer issues...

I just installed a FMF Q series pipe on my 99 YZ400 and I have noticed a few things and was wondering if anyone else has seen the same problems.

First off, I can't use the circular gasket between the header and silencer because the clearance is too tight. Tried teflon tape and hi temp RTV, both of them blew out, duh..

When I was washing my bike today, I noticed the silencer has a dent in it from my brake caliper when I bottomed the suspension. What the #$!@#$? I thought they would do some research on the fittment of this pipe before selling it to the public. I'm pissed...


I know that the stock pipe has been 'pre-dented' for rider convenience. I run the fmf IV and have not dented it yet...but then maybe I have not gone as big as you yet :)

I know with my pipe there is no gasket required and you just slip it on and tighten it up...there is a VERY slight leak between muffler and header but nothing to worry about.


You can also use the chamber seal on the area between the header and the silencer.


00'YZ426F 00'XR50R LATER DAYS!!!

Could that dent have been put in there from FMF just like the factory silencer? Can you see where the caliper hit it and left scratches or marring behind?

[This message has been edited by Boit (edited 08-03-2001).]

The dent in the pipe is new as the pipe had no cut out for the brake caliper till I unknowingly put one in it while coming up a little short on a double. As far as using the chamber seal, I have just enough room to get the silencer on over the stock header, not much room for anything else. I tried installing it with no gasket between the silencer and header and the leak was very apparent. The bike now also pops because of the exhaust leak sucking cold air into the hot exhaust. I called FMF and told them what was going on and they said to send them the pipe and they will look at it and let me know in a few days what they are gonna do. The tech I spoke with said that they are fixing the leak with hi-temp RTV, I told them if that is the fix, to keep it and I'll slap my old Power Core 4 back on and continue to deafen the world. What can you do? Does anybody know if a stock 2001 426 header/silencer will fit a 99 YZ400? I'm beginning to think that stock wasn't that bad...


I have the same problem with an FMF Megamax II muffler on my 99 WR. I made a "gasket" out of very thin sheet metal I got from Home Depot (thin enough to be cut with tin snips), about an inch wide and the same length as the circumference of the end of the header pipe. I wrapped that around the end of the header pipe to bend it into a cylinder in order to make it into a gasket. Push this gasket into the end of the silencer once the shape is cylindrical. If yours is like mine, there's a lip near the end of the silencer pipe and if you get thin enough sheet metal, it should be able to slip right into that lip. That whole thing should be able to slide right over your header pipe. If it's too tight, use some wide pliers to bend out the flanges on the end of the pipe so it will slide over the header pipe. I did that on mine and it works pretty good. There's a slight leak that I periodically seal with RTV sealant, but it disintegrates after a while. It's time to reapply it on mine right now. Oh well, I guess it's time to repack my muffler anyway...

Make sure you let that high temp RTV cure for at least 24 hours before you run the engine. I've been using ultra-copper and it lasts about 15 hours riding time between applications.

Hope this helps.

I know they changed the header for ’00 (and again for ’01), I’m thinking the older models have a smaller diameter at the tail pipe connection.

On my ’01 the FMF Q, the one as big as a KTM can, fits snugly to the header. I never noticed any leaks, but I was just looking at it and it appeared I had some blow by. The clamp wasn’t very tight, but I went ahead and made a few wraps with teflon tape as other guys have suggested.

This pipe clears my caliper, as I am sure I have used all the travel many times and there are no dents in the can.


did you fit the band on your fmf Q the right way round, so the silencer is mounted farthest away from the tyre? I've noticed it could go either way, next time I service the linkage I will check the clearance, if I haven't dented the silencer by then!!

scooby thumbs.gif

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