BS or what? Doesn't feel like it.

9 replies to this topic
  • Rich_in_Orlando

Posted August 12, 2002 - 04:26 PM


My bike had been having a radiator problem. Coolant wasn't sucking back into it as it cooled down. I thought it was the cap, so I replaced it, but that didn't fix it. I noticed a tiny coolant leak at the base of the cylinder and realized it was the o-ring that was leaking. This was Friday night (and I must ride Sunday!)

Saturday morning I started rounding up the parts to fix it: new head gasket, base gasket and an o-ring. Everything but the base gasket was available. I was able to locate a YZ base gasket about 60 miles away. (Good excuse for a fast road trip on my street bike.) Different part number but it would work. I was told that the YZ gasket increases compression because it's a little thinner and I'd have to run with YZ timing to deal with that. I was already running YZ timing so I figured "no problem".

More compression equals more power, right? Well, it sure did feel like it had more power! Admittedly, conditions on Sunday were nearly ideal due to a cold front that had dropped the humidity and it wasn't too hot. But it ran very strong--better than it ever has as far as I can tell.

Is it my imagination or could the YZ gasket truly be enhancing performance? (I thought WRs and YZs both had a 12.5:1 compression ratio.) If I'd have known about this, I would have replaced the gasket long ago. BTW, the new o-ring fixed the radiator problem.

  • tk421

Posted August 12, 2002 - 06:35 PM


Hmmm, that’s interesting. Another MOD.
Thanks Rich!

  • Mark_Cantrell

Posted August 13, 2002 - 03:36 AM



The O-ring is the one that comes out of the front left side of the head. The one you have to remove to get the head off? If so, why did you have to remove the head to change it?

The cometic base gasket is the same between the WR and YZ. And I'd be shocked if the difference between two paper gaskets could be noticed. Could the cooler weather have been the difference you noticed?


  • Rich_in_Orlando

Posted August 13, 2002 - 04:52 AM


The o-ring that was leaking joins the cylinder to the crankcase on the front right side of the engine. The one you're thinking of connects that pipe that goes from the cylinder head to the left radiator. I've had leakage with that one too, but that's an easy fix. A little teflon tape around a new o-ring fixed it right up.

The temperature was just a little cooler than it has been- about 88° vs 95° F. If the weather did make it run better, I'd bet the lower humidity affected it more than the temperature. But that's what I'm not sure about and it made me wonder if the thinner gasket/higher compression I was told about was BS. I do know it did run better. I drag raced a guy on a very strong running XR650R and while he did pull away from me, it was a good close race and we both reached the same approximate top speed. Bouncing off the rev limiter is an interesting experience.

  • SFO

Posted August 13, 2002 - 06:20 AM


when I was building my wr I noticed the same thing.
wr 426 has .080" deck height w/stock gasket.
yz gasket .050" deck height.

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  • evl2evil

Posted August 13, 2002 - 04:39 PM


I'm not sure about the size difference between a yz and a wr gasket.I do know that putting a thinner gasket either head or base gasket result's in more compression,which in turn create's a harder hitting motor.I haven't had to rebuild my wr yet but i've done this with every 2 stroke i've ever rebuilt,it alway's give me a harder hitting motor.

  • lewichris

Posted August 14, 2002 - 03:58 AM


why dont you grind the head down a bit. That would do it for you right. That is what the 2 smoke guys do to get more power out of their motors. But then again they dont have a valve train huh. HMMMMMMMMMMMMMM!!

  • tbronc

Posted August 14, 2002 - 07:55 AM


it can be done, it has been done... though there's a little more to it than just a grinder :)

didn't you do this SFO? -(along with many things)

  • SFO

Posted August 14, 2002 - 09:51 PM


I ended up with my deck height at .035"...
among with some other things... :) :D

  • Rich_in_Orlando

Posted August 14, 2002 - 04:16 PM


What is "deck height"? :)


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