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  1. #1

    Join Date
    May 2010
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    Too lean/bad fuel, detonation? something made the piston ring break?

    Just wondering if anybody has any ideas on what happened to cylinder number one on my 2000 GPR with stage 2 Riva setup? I noticed that the porcelain on my plugs were more white than usual since the last rebuild when I put Gas Power Valves on it. I opened up my high speed screws an extra half turn but still had this happen after only about 10 hours on this cylinder After talking to Dale in Texas at Dales Motor Sports, he thought photos show it was detonation that made the piston ring grab the exhaust port? I can start using half racing fuel/half premium gas (pre mix) to see if that solves this problem? Drove the machine very easy without hardly any top speed runs (girlfriends ski). Any ideas or preventative steps to take would be greatly appreciated. Thank you Green Hulk for your knowledgeable forum users. slight nick in power valve but I think that might have been the ring that bounced around inside the cylinder when it left through the exhaust port? Dale didn't think that it was the valve grabbing the piston ring?
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  2. #2

    Join Date
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    more photos

    more photos. Other head had a power valve break off and dinged up the cylinder but that cylinder didn't seem to be affected by the dents? Should I try to file the dings down or send them in with the cylinder to Millennium to fix when they re-chrome it?
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  3. #3

    Join Date
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    you can file down the sharp ones. if you don't it might get red hot and act like a spark plug lighting the fuel.
    I can't see your picture properly, it is so bright. on the first piston picture it look like you have the ring gap facing the exhaust? if that is the case you install the piston the wrong way.

  4. #4
    Happily Self-Employed WFO's Avatar
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    Nov 2005
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    2 strokes pistons have a hole on the intake side just below the rings, so the piston doesnt appear to be in backwards

    Most common cause of that type of failure is when the piston ring locator pin falls out or recesses to far inward, letting the ring opening walk around to the exhaust port, then hooking the port and scoring. You can tell the ring hooked the port. Look at the other side of the piston and see if the locator pins are still there

  5. #5

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    Pictures also look like the piston top is dry with and not much sign of wash pattern. You mentioned plugs looking whiter, should check out fuel delivery also, #1 is the last to get fuel on a stock setup. Turning the high speed screw out only helps the very high rpm mixture and will not help if you are lean at 3/4 throttle.

  6. #6
    WFO is right,,, check to see if the opening of the piston ring/s are at or near the locator pin location. i bet they are not. even if the pin is still in place depending on the piston and ring manufacturer, the ring can get under the pin and spin around far enough for the ring to snag. ask me how i know....

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