Piston ring

Four-stroke engines usually have three rings: the top compression ring, the second compression ring and the oil control ring. Rings are sold in standard (STD) or oversize (e.g. 0.25 / 0.50 mm) sizes to match the piston.

Signs of wear

• Blue exhaust smoke, oil consumption
• Low compression, loss of power, hard starting
• Higher crankcase pressure (oil mist from the breather)

When fitting, measure the ring end gap and stagger the gaps at the angles given in the manual.