Jan 14, 2007
went to start my bike this weekend and it had zilcho compression. it tried to start but just popped once and died. so i noticed a little coolant coming out of the head. btw this motor uses 2 rubber o-rings. i have probably no more than 10 hours on the new piston which looks great would it be a good idea to put a new one in with that amount of time or just ring it and put new o-rings in.


Jul 19, 2007
I would get a new top end gasket set because you will have to pull the head and cylinder off anyways. With the little experience I've just done with re-doing the top end of my '98 yz125, you might want to check the tolerances of the cylinder bore and the piston size to make sure that you won't have to have the cylinder bored. Make sure that when you get the new ring(s), place it in the cylinder and square it up with the piston and then check the gap clearance. File down the end of the ring according to the specs of your manual and don't forget to smooth the sharp edges of the end. If your piston doesn't have any stress cracks in the skirt and there isn't too much carbon build up that you can't clean off, then re-use the one you have if you need to get back out and ride. I would replace the piston myself because of peace of mind!


Jul 15, 2007
well 10 hours is nothing presuming that you dont ride lke you stole it, you run 32:1 with good synthetic, maintenece regularly(air filter etc).

ten hours is not enough to replace the piston or rings, really it depends on how you ride.


Oct 19, 2006
If the piston really has only 10 hours on it and an inspection through the exhaust and intake ports reveals minimal wear, I would just replace the o-rings. You have to wonder why the gasket blew, though. Did the o-rings simply lose their resiliancy? Was their dirt or imperfections on the sealing surface. The head studs not properly torqued or the head warped? Or, was the bike run into severe detonation?


Aug 31, 2005
on my rm it also has the 2 o-ring set up.
and in my experience with rebuilding it that the o-rings never
set true and sometimes you get a flat spot on the o ring.
i would take the head off and check the o-ing.
before doing full rebuild just my .02 from past problems


Crash Test Dummy
Jul 18, 2006
Amo, IN
whenfoxforks-ruled said:
I lick and rub the o-rings to lay properly,that they stay is absolute! 10 hours on the ring is time,rings can last longer.

I lick and rub something to get it to lay down, but not o-rings.. :rotfl:

Shut Up Pred!
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