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 x Stroke||Compression Ratio|
|139QMB||49.5 cc||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||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||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 139QMB variation of the GY6 engine is available in version with 4-valve cylinder head, which has maximum output of 2.6 kW (3.62 hp) at 7500rpm.
The GY6 engine family is produced by a wide range of manufacturers throughout Asia, and as such there may be many small differences between engines from different firms.
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