The GY6 engine was originally developed by Honda for use in its motor scooters. It was later adopted by many scooter and light vehicle manufacturers (ATV etc.) across Taiwan, PRC and South East Asia. The 150cc examples are popular alternatives to 50cc Honda Ruckus owners as candidates for engine swaps.
Contents
Configuration
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).
Variants
Specifications of GY6 variants
The GY6 engines are produced by many different manufacturers in Asia such as Kymco, SYM. There are some minor differences between the engines which slightly reduces parts interchangebility between different gy6 engines. Commonly, the piston/cylinder bore measures 57mm for scooters, and 57.4mm for karts, quads, and buggies (and often features a reverse gear in the engine case).