ENGINE Bore, 70 mm. Stroke, 84 mm. Capacity 649 c.c.
This modern power unit of new design has many features which are entirely original.
The cylinders, while cast "en bloc" are vertical, side by side, one cylinder each side of the centre of the crankcase (having a firing angle of 360 degrees). and have adequate air passages between them. They maintain the characteristics of two single cylinders, having separate detachable single port heads.
The valve gear (two valves per cylinder) is operated by push rods fully enclosed and working between the two cylinder barrels. These are actuated by a cam shaft, running in oil, mounted on ball bearings, positioned in the top of the crankcase and to the rear of the cylinder base. The crankshaft is of the solid forged type of great strength and is mounted on extremely large ball bearings at each end.
The two conrods are fitted with split white metal big end bearings of ample proportions (1 1/4in. x 1 3/8in.) and these bearings are lubricated by pressure fed oil delivered through the crankshaft. The drive is taken through two double helical gear wheels (first of which contains an engine shaft shock absorber) to a four-speed gearbox, which is in unit with the crankcase, but which is readily detachable should this be necessary. These gear wheels run in a die-cast aluminium case (the inner half of which is integral with the crankcase) The lubrication system is entirely independent of the main engine supply.
The magneto is gear driven and there is, in fact, no chain employed in the whole power unit and gearbox. The main oil sump in the crankcase contains four pints of oil and this supply is supplemented by a further pint of oil contained in a separate oil tank, which cleans and cools the oil in circuit, the whole circuit, therefore, having a capacity of five pints.
CARBURETTER Amal 7/8in. flange fitting.
IGNITION Lucas H.T. Magneto or Magdyno (extra).
GEARBOX Integral with crank case. Four-speed four-plate clutch; hand operated.
FRAME New design Duplex type of best quality weldless steel tubing giving low riding position.
FORK Girder type of new design. Very robust taper tubing with straight front girder. Compression spring, fork dampers, and steering damper.