O.S. Engines 18TM Revo - Manual (Page 7)

ENGINE CONSTRUCTION
With this engine, the piston will
feel tight at the top of its stroke
(TDC) when the engine is cold.
This is normal. The cylinder bore
has a slight taper. The piston
and cylinder are designed to
achieve a perfect running
clearance when they reach
operating temperature.
Cylinder Liner
When the engine is cold. When the engine-is hot.
Near TDC
Piston
Crankshaft
Slight taper
6