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Yamaha MX & Off-Road Dirt Bikes
1999 yz250 Oil from Exhaust
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[QUOTE="Solid State, post: 1159623, member: 22186"] KX250Dad, I have chased this condition for years. According to Erik Gore, these mass produced cast cylinders (and heads) can leach water straight through the aluminum due to porosity of the metal. A cylinder and head swap would rule that out. Unfortunately, it did not in my situation ($249 plus shipping). Head gaskets (o-rings) and base gaskets are obvious candidates, but I'm sure you've ruled those out as well. There is another source that is possible. If you study the exploded diagram for the left/right cases, you should see that the water pump pulls/pushes coolant from the right side case to the left side case to feed the cylinder up through the water jacket on the left side of the cylinder. There is a round channel in the front of the cases (internal) to facilitate this transfer. The cases, of course, are split down the center (really stupid but a universal approach) and the channel is sealed with liquid gasket and an o-ring. A leak in this area will put water into the bottom end and thus enter the combustion chamber. Grey spooge may also be evident exiting the power valve vent tube and not necessarily the exhaust. Good luck. [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
1999 yz250 Oil from Exhaust
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