ORIGINAL: DLT
Jim, this seems unusual...I just took the back plate off my 50SX the other day and I was shocked at how BRIGHT it was inside (I also use Wildcat/Hobbytown...10%...cas/syn w/ extra oil added to get up to 20%). About a year ago I installed high speed high heat bearings, so no rust.??....Dave
Inside was nice and clean and bright, except the carbon on the piston head and heat stains on the liner and piston.
There was a considerably amount of varnish all over the top of the head and under the head where it mates to the crank. I also notices rust on the surface ring of the rear bearing, but not the bearings themselves.