Hi there,

I recently bought a NovaRoss .12 engine and finished run in with about half gallon on it. When I disassembly the engine for maintenance, I found that there is a coat of black, tar like, stuff stick on the top of the pistol surface. I tried to use motor spray to rub it but couldn’t clean it off. Does anyone here has an idea about how can I remove it or it is normal to have it on the piston.

Thanks

PS.. Im using Blue Thunder 20% fuel...