What the heck

I bought ten new spark plugs that seem to fit all my engines so I thought I would turn the 31cc ww engine to make sure it was hitting the plug. I noticed a grinding sound at the top end. I tested to make sure it wasn't the plug. It did it with two other plugs that were the exact match for the bike.

What would cause that grinding sound at the top of the stroke. I hope it is just carbon accumulation. Silly me lol. It does not seem to effect the engine performance. I plan to run it till it blows anyway but I am curious.

These engines are cheap enough to be throw aways.

I think the ryobi is a great helper engine. It really would make a great bike for someone in a flat area. The minor hills in a reasonably flat area wouldn't be any problem for it.