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Thoughts about piston rings


Hemberg
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Good day everyone

My pap pa 125 broke down a few weeks back, this time it was the piston ring that caused a broken piston and some scratches into the cylinder. Probably my own fault since I should have changed piston ring earlier. but...

The opening of the piston ring passes a port on the old piston. When I changed piston the opening of the piston ring is in another position.

I don't know if that makes any difference but i sound like a bad place to have the opening of the piston ring in the same place as a port opening, right?

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Right !!

never never the gap goes past the port.

They shouldn't line up either if there is more than one ring.

Usually go against the side walls.

Sometimes the location pins for the rings have been known to fall out with m/cycle engines allowing the rings to turn .

If you give it a tug with some pliers (the one in the old piston) you may find its just wedged in the groove rather than embedded in the piston in the groove.

Hope you get it sorted soon

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Makes sense not to have the opening towards a port. The motor broke because the open end of the piston ring hit the exhaust port opening and got stuck and broke the piston and cylinder.

The original piston that came with the motor had this configuration (location pin at the exhaust port) The one I got to replace it doesn't ( that one came also from pap). The replace piston is a HE piston with graphite coating.

So for those that have an early pap pa 125, make sure not to wait too long to change piston ring. Maybe might as well change the piston.

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  • 2 weeks later...
  • 1 month later...

Well I probably was wrong, after looking at the piston more carefully the retention pin had probably broken off somehow and the piston ring turned 180 degrees and got caught, anyway pap consider it being a warranty issue so that's good news. They are not sure how it happened but wants me to check the squish so I'm going to do that before I run it again.

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They gave me a pdf (in spanish) it's too big to include in the message, but mess me and we'll sort that out.

there seems to be similar info on youtube as well, how to check it. The technique used is to remove the spark plug and squish solder on the top of the piston and then measure the solder. Quite clever I must say.

Haven't got any info about ignition timing.

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