A 399 cc parallel twin
The Z400 engine has two cylinders side by side (70 mm bore, 51.8 mm stroke), liquid cooling and double overhead cams. It makes about 45 PS at 10,000 rpm.
180° crankshaft
Each piston drives its crankpin through a connecting rod. The pins are 180° apart, so one piston rises while the other falls.
Valve train
A chain from the crank drives two camshafts at half crank speed. Their lobes open four intake valves at the back and four exhaust valves at the front: 8 valves in all.
Four strokes
Air and fuel come in through the intake, are squeezed about 11.5 to 1 by the rising piston and lit by the spark plug; the burnt gas leaves through the exhaust. With a 180° crank the cylinders fire 180° and then 540° of crank rotation apart, an uneven beat.
Balancer shaft
With a 180° crank the pistons pull opposite ways, so the engine wants to rock end to end. A gear-driven balancer shaft with offset weights cancels that rocking.
Clutch and 6-speed gearbox
The primary gear drives the slipper clutch on the input shaft. Six constant-mesh gear pairs pass power to the output shaft, whose sprocket drives the chain to the rear wheel.