EC300 Cylinder problem
 

Hi there,

I recently got my cylinder back from coating and rebuild the whole top end. After 5 hours of use the cylinder looked like the first picture. I asked the dude that coated my cylinder what could?ve caused those marks. He told me that the ring clearance was too small and I should get new rings and hone the cylinder. After I sent him the cylinder again to hone it and got new rings I put the ring clearance to 0.4mm on both the top and bottom ring. I rebuild it again, let it run for 3x10 minutes and the cylinder looks like that again. Has anyone on this forum have an idea of where those marks could come from?

What does your piston look like? Do you warm it up properly before going hard on the throttle? 99% of two stroke rings barely need any clearance adjustments if at all.
To me that looks like a cold seizure.

Hmm. If it were me I'd dress the areas with scotchbrite, open the gap to a safe 0.6 and never look inside again.

Like I said, I didn?t give it throttle at all. I just let it idle with some 1/4 throttle in between to warm it up. In the second picture I didn?t even ride the bike. It came just from the idle.

W?ssner recommends 0.29mm for the tip ring and 0,36 for the bottom ring so it should be a safe Gap.

Are you using an A, B, or C piston and what size was the cylinder plated for?

I'm running Wossner and have had jug off after many hours after following ring clearance recommendations with no issue.
But clearly something isn't working. Youd lose no power. But hadn't considered SS109s idea??

I have been running a Wossner with 0.4 end gap on top and bottom rings for years. Just an idea but are the numbers on your rings facing upward?

A Piston with Cylidner plated for A Size

Yeah, I made sure the numbers were on top.