Olgerz

Is it OK to fit chinese 150ccm or Airsal cylinder is the only choice? Not gonna live forever with my YBR, prob selling it.

Thank you for replying. Piston is OK, no holes, rings seems to be also OK - don't know how to measure them. Will replace all parts anyway. Valves are opening and closing properly in my opinion - should I replace the valves and other parts? What about that periodic humming sound? Could it be bearing or something? Don't want to open both crankcases for nothing..

Hello! First time here, non english, so forgive me for any typos etc. My YBR 125 engine (on Derbi Senda frame) started to make weird noise. Before that engine ran smoothly. Now power is lower than usual but it runs and shifts like it should. Link to video: https://www.youtube.com/watch?v=blPZ5RVSqEQ What it could be? I've opened the engine up and no major flaws are seen. Im changing 125cc to 150cc anyway.