Crank Case and Flywheel

The crankcase contains the crankshaft of the engine. This converts the reciprocating motion of the piston into a rotary output motion via the connecting rod coupling the piston and the crankshaft.

The camshaft that operates the inlet and exhaust valves is also in the crankcase and is directly gear driven from the crankshaft at half engine rotational speed. The cam lobe profiles determine the times of valve opening and closing with respect to the position of the piston in the cylinder.

Outside the crankcase are two flywheels. These store energy and provide the work don on the cylinder gas during the compression and exhaust strokes. The flywheel also carries a reflecting coupon that provides a signal for the electronic ignition system. Moving the timing photodetector alters the ignition timing of the engine.