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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Cometic EST Gaskets - Extreme Seal Technology
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[QUOTE="extreme33, post: 1408537, member: 26196"] The next rebuild I'll reinstall new nuts and studs but don't think it's the problem. When the bike was a stock 250, I rebuilt the top end a few times using the same hardware and the problem wasn't present. I don't remember the exact torque increments used during installation. Any recommendation on an increment amount? The leak increasing over time. The first ten hours there isn't any coolant loss. Then it slowly starts to loss coolant at a rate of 1/4 capacity per hour. It's starts to escalate from the 10 hour point to the 20 hour mark. At the end it's half empty after 10 minutes. My first thought was overheating but further investigation concluded head gasket leak. I attached a small plastic bag to the overflow hose to contain the antifreeze. Once you let it settle, you can see a fine skim layer of black on top. I'm assuming it's the exhaust gas / carbon. Also, if you remove the radiator cap and start the bike, you'll see very very small bubbles on top during idle. If you rev the bike, it's difficult to see an increase since the whole bike vibrates. Pressure test doesn't work well since the leak starts out so small. It needs to be track tested / hard riding to create coolant loss. Running on the stand didn't show any increase in pressure on the gauge. I also did a combustion leak test which test for exhaust gases in the antifreeze. The color turned from blue to yellow which confirms the presence of exhaust. I still believe it to be an inadequate seal by the gasket. I find it ironic that Cometic now makes the same gasket set but with "Extreme Seal Technology." Shouldn't the standard gasket be sufficient? [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Cometic EST Gaskets - Extreme Seal Technology
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