I bought a brand new OPS 3.5 Buggy engine (.21 size) which won't crank.
I measured the sleeve, it has 16.5mm at bottom and tapered to 16.0mm at top (approx 3mm from top of sleeve). The piston diameter is 16.2mm
My question: is it normal to have 20micron interference of piston and the top portion of the sleeve? I couldn't turn the flywheel, and my starter box couldn't crank it even when i tried heating up the top of the engine.

On the other hand, my OS .21 VR can be turned using the same starter box even when it was new.

Any advice?

Thanks in advance

ops may have a more tighter tolerance at top dead center when new as far as breake in go to the engine wont run thread on the second page of the nitro engine zone i posted my brak in methed their, it works grat and that motor will last. the motor may need to be heated up quite a bit, if 200 to 220 dont do it then apply a little more, but once you get it going you will have to keep heat on it or it will lock up from cooling down. good luck

Thanks mugenb46 for the input.