GY6 engine


The GY6 engine design is a four-stroke single-cylinder in a near horizontal orientation that is used on a number of small motorcycles or scooters made in Taiwan, China, and other southeast Asian countries. It is believed to have originally been a Honda design. At some stage Honda used Kymco, a Taiwanese company, as a factory for Honda bikes. It has since become a generic technology. Kymco went on to produce Honda clones such as the Pulsar, made to Honda standards, as part of their range.

Configuration

The GY6 single is forced air-cooled, with a chain-driven overhead camshaft and a crossflow hemi cylinder head. Fuel metering is by a single constant-velocity style sidedraft carburetor, typically a Keihin CVK clone or similar.
Ignition is by capacitor discharge ignition, with a magnetic trigger on the flywheel. Because the trigger is on the flywheel instead of the camshaft, the ignition will fire on both the compression and exhaust strokes, making it a 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 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.