The GY6 engine design has been adopted and tweaked by many scooter and light vehicle manufacturers (ATV etc.) across Taiwan, PRC and South East Asia. The exact origins of the design are unknown, and while it is often claimed to be a Honda design, no Honda products have ever been produced with a design resembling that of the GY6.
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, known as "wasted spark" ignition". An integrated magneto provides 50 V AC power for the CDI system and 20-30 V AC rectified and regulated to 12 V DC for 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 engaged via a centrifugal clutch at the rear pulley in the same fashion as Vespa Grande, Bravo and variated Ciao model, as well as Honda Camino/Hobbit scooters/mopeds. An electric starter, backup kick-starter, and rear brake hardware is also housed in the swingarm. There are variants known as the "short case" (10" rear wheel, 729, 735 or 742mm belt) and "long case" (12" or 13" wheel, 835 or 842mm belt). Final gearing ratio can be as low as 13/40, or as high as 18/36 (more commonly available as aftermarket items).
|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 engines are produced by many different manufacturers in Asia such as Kymco, SYM, and Znen. Kymco and SYM retained GY6 labelling for their engines as well. There are some minor differences between the engines which slightly reduces parts interchangebility between different gy6 engines. The different types of gy6 engines are recalled as gy6-a, gy6-b, gy-6c. Karts,quads and buggies often features a reverse gear in the engine case.
- "About GY6 Engines & Components". Retrieved 17 February 2015.
- "La verdadera historia del Motor GY6". 27 October 2011. Retrieved 17 February 2015.
- "MOTORCYCLE ENGINE-Products World— 1P39QMB 1P39QMB". Retrieved 11 September 2015.
- 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.