GY6 - the little engine that could!

GY& - the little engine that could

 In love with a tiny engine 

About the Engine

Who made it first? It is discussable, but I believe it was developed by Honda in the 1980s and used in their Elite and Spacey line of scooters. Now abandoned by Honda it has been licensed to several Chinese and Taiwanese engine producers.

Honda GY6 engine

Old Honda made GY6.

The engine design is a single-cylinder, four-stroke engine, in a horizontal orientation. It is by fan air cooled, anf has a chain-driven overhead camshaft with a crossflow hemi head. Fuel is delivered by a constant-velocity style sidedraft carburetor,normaly a Keihin CVK clone or similar.

The ignition system is by CDI (capasitor discharge ignition), 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.

The package 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.

The engine is now widely used in Far East scooters and ATV's

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

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