The GY6 design is a single-cylinder, four-stroke engine, in a near horizontal orientation. It is forced-air cooled, with a chain-driven overhead camshaft and a crossflow hemi head. Fuel metering is by a single constant-velocity style sidedraft carburetor, typically a Keihin CVK clone or similar.
Ignition is by CDI, with a magnetic trigger on the flywheel. Because the trigger is on the flywheel instead of the cam, the ignition will fire on both the compression and exhaust strokes. An integrated magneto provides 12 v power for the CDI system, chassis accessories (such as lighting), and to charge a battery.
It includes an integrated swingarm, which houses a centrifugally controlled Continuously variable transmission (CVT) using a rubber belt sometimes called a VDP. At the rear of the swingarm, a centrifugal clutch connects the transmission to a simple integral gear-reduction unit. There is no clutch of any kind between the CVT and the crankshaft; it is permanently engaged. An electric starter, backup kick-starter, and rear brake hardware is also housed in the swingarm.
|Engine||Displacement||Power||Bore × stroke||Compression ratio|
|139QMB||49.5 cc (3.02 cu in)||2.95 hp (2.20 kW) at 7,500 rpm||39 mm × 41.4 mm (1.54 in × 1.63 in)||10.5:1|
|152QMI||124.65 cc (7.607 cu in)||6.8 hp (5.1 kW) at 7,000 rpm||52.4 mm × 57.8 mm (2.06 in × 2.28 in)||9.2:1|
|157QMJ||149.6 cc (9.13 cu in)||8.6 hp (6.4 kW) at 7,000 rpm||57.4 mm × 57.8 mm (2.26 in × 2.28 in)||8.8:1|
The GY6 engine is made by many different manufacturers in Asia, so there are many small differences between the engines.
- Chinese Taiwanese & Korean Scooters 50cc Thru 200cc, '04-'09: 50, by Max Haynes and Phil Mather. Haynes Manuals. 2009.
- Interfirm relations under late industrialization in China: the supplier system in the motorcycle industry; Volume 40 of I.D.E. occasional papers series. Moriki Ōhara. Institute of Developing Economies, Japan External Trade Organization. 2006. ISBN 9784258520404. p. 44, 53. Full text at HighBeam Research
- The Little Book of Trikes By Adam Quellin. Veloce Publishing Ltd, 2011. ISBN 9781845842956. p. 64.
- Scooters Service and Repair Manual. by Phil Mather and Alan Harold Ahlstrand. Haynes Manuals. 2006.