Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: apossin on November 29, 2012, 04:47:17 PM
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Purchased the bike seized. Tore it down. Piston broke and locked it up. New bottom end, replayed cylinder, new top end. While putting the top end on I had problems. Lubricated new piston and cylinder, tightened cylinder down. Turned motor by hand with flywheel weight. Everything felt good until the piston was at the bottom of the stroke. Something was in a bind and I could no longer turn it either way. Removed cylinder nuts and took pressure off the base gasket. I was then able to turn it again by hand but could hear metal to metal contact at the bottom of the stroke. Pulled it apart and I can't find any evidence of where the contact is happening. I believe the skirt on the bottom of the cylinder is contacting the crank on that portion of the stroke. Almost like the crank is not perfectly round. Any help or suggestions would be greatly appreciated. I was considering lightly coating everything with some grease to see where the contact is happening.
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The grease idea sounds like it would show you where its happening. As long as it isn't the rod hitting the bottom of the crank case.
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Shrapnel from grenaded piston stuck under the crank?
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Turns out the skirt in the intake side of the piston was contacting the cases at the bottom of the stroke. After filing it down I have no interference. Hopefully it doesn't blow up but only one way to find out. Note to self: never buy another Namura piston. Cheap isn't always good. Never had a single problem out of a wiseco so that's what ill stick with from now on.
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Somebody sell you the wrong piston?
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Do you have the correct year piston. The rm motors changed abit between 01-03.
Not sure if the piston changed but worth a look.
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make sure its got plenty of clearance for when the piston expands at runnng temp.
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Something is not right... I've used Namura pistons in the past with no issues... You've got too much invested to just slap it back together. Step back and review you parts and ensure everything is correct.
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Something is not right... I've used Namura pistons in the past with no issues... You've got too much invested to just slap it back together. Step back and review you parts and ensure everything is correct.
This. You don't want to wait until your piston gets a smiley face ground into it before you start doing something about it. Depending on the conditions of the previous seizure, your cylinder may be slightly warped. If only ever so slightly.
Don't wait for it to grenade before you investigate the issues, thats an idiots path. Take cylinder measurements, compare them to the piston. Check your piston part no. and compare it to OEM. Compare everything.
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I'm not sure if the front/rear profile is different, but the piston isn't in backward is it?