I tried to rebuild a stihl br600 engine I got from a unit I bought that didnt run. I installed new crank bearings and seals. the valves look almost new and are clean, installed new rings, honed the cylinder. checked the valve clearance. cam gear is ok. installed new spark plug. when I turn the flywheel it doesnt seem to barely have any compression. when I cover the exhaust port with my thumb the compression is good. what would cause it to not have compression when everything looks like it...
Stihl br600 no compression
Stihl br600 no compression