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The development history of a 30cc 2-stroke engine power unit in the covered rear wheel for retrofit into standard bicycle chassis. The rear wheel acts as cooling fan for the air cooled long stroke engine with catalyst exhaust system, autochoke carburetor, autolube oil pump, electric start and inertia start, single speed automatic transmission and 7 speed hub final drive. The space in the rear wheel contains intake air filter, exhaust system, fuel tank, oil tank and engine with drive train, the complete engine being only 94mm wide. The complete covered power unit is nearly undetectable as the rear wheel covers resemble road racing bicycles. There is very low stationary and pass-by noise (64 db[A]), no exhaust gas opacity or smell, very low vibration level and very good fuel economy up to 133 km/l.

The market for handheld engines such as chainsaws, brush-cutters and for 2-wheeler applications like scooters, mopeds and minimum transportation vehicles shows a strong tendency towards 4-stroke application due to environmental and image reasons. The ranking of the priorities like Weight - Cost - Performance in these engines differs and beside this the fulfillment of the legal requirements for pollutant emission, noise and the expected fuel economy lead to a different approach for the layout of the cylinder-heads showing different optimum solutions dependant on the casting technology, whether pressure die cast or with sand cores. The variations include the number of valves from two to four and the arrangement of the valves and spark plugs. The porting and combustion chamber layout, including data for flow rate and charge movement concepts, are stipulated for the cylinder bore of 41 mm.