Engine seizure

Seizure (seizing, freeze-up) happens when moving parts lock together, usually because of overheating or lack of lubrication. In an engine, the piston expands and welds itself to the cylinder wall, or a bearing overheats and grabs the crankshaft. Bolts and fittings that rust or gall together are also called seized.

Two-strokes are especially at risk if they run lean, have the wrong fuel/oil mix or the oil pump fails. Warning signs include a sudden loss of power, a tightening or squeaking feeling, or knocking. A full seizure can lock the rear wheel, so pull the clutch immediately.

Prevent it by keeping oil and coolant at the right level, using the correct mix and jetting, warming up before hard use and running in new pistons carefully.