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6/15/2014
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Salamanca, NY
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I have a 2003 CR125 that has blown up on me twice since I've rode it. I have probably 8 hours on the bike TOTAL between the 2 rebuilds. The first time it blew up it had a crappy Namura piston in it, no cylinder damage on the inside. I rebuilt it the same why I have with my other bikes over the years....and it blew up AGAIN. I did the same break in as I always do and have NEVER had a problem. Ran a Pro-X piston, pre-lubed everything. When it blew up this time the cylinder got damaged, the sleeve is toast on the intake side. The ring appeared to have caught a groove and just keep working until it couldn't go anymore. I run my gas 40:1.
I don't want to overthink this at all but for it to blow up twice in less than 10 hours of owning it, both pistons are damaged on the side where the intake is. I ordered a complete rebuild kit, top and bottom. I found that the crank seal on the flywheel side was leaking (had gas on it) and was leaking to the flywheel.
I guess my question is, would you build the carb too at this point? Has a PC pipe and silencer
I don't want to overthink this at all but for it to blow up twice in less than 10 hours of owning it, both pistons are damaged on the side where the intake is. I ordered a complete rebuild kit, top and bottom. I found that the crank seal on the flywheel side was leaking (had gas on it) and was leaking to the flywheel.
I guess my question is, would you build the carb too at this point? Has a PC pipe and silencer
rebuild again bottom up and make sure the piston is matched for proper clearance to the cylinder. steel sleeves are hard on pistons and do not expand as much as aluminum so you may be able to get away with slightly less cylinder wall clearance.
set your ring gap at the maximum as a steel sleeve will run hotter than standard and cause the ring to expand more, you need the room.
lastly, Run leaded fuel (I LOVE 100LL AVGAS) and mix at 28:1 with a good synthetic oil like maxima K2 or motul 800
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