THE 6 CYLINDER SCOTT TWO-STROKE

THE 6-CYLINDER SCOTT TWO-STROKE

VERY considerable interest was aroused by the picture of a 6-cylinder Scott 2-stroke engine installed in a 1928 Aston-Martin, published in the December, 1943, issue of MOTOR SPORT, so we have pleasure in adding further details of the engine, kindly supplied by the owner, Dr. IL Wood. The Scott Company is normally associated with the famous 2-stroke motorcycle which it introduced before the last war, and with the curious 2-track, :3-wheeled Scott “Sociable “of the early nineteen-twenties. Some time before the outbreak of the present war a 1-litre 3-cylinder-in-line 2-stroke engine was announced, and experimentally installed in a popular make of small car. The 6-cylinder 2-litre 73 x78 mm. version which Dr. Wood had installed in an Aston-Martin in 1937 was a development of the 3-cylinder engine. Designed by Mr. Cull, it has called forth praise from Cecil Clutton and, indeed, showed a remarkably high output, giving 80 b.h.p. as supplied, while the designer claimed that it could c.isily be developed to give 120 b.h.p., or 170 b.h.p. unblown, if somewhat modified. The engine was of normal 3-port type., with cast-iron block and aluminium head, crankcase, sump, inlet pipe and transfer port covers. The crankshaft was of built-up 6-throw type

With disc webs, running in eight doublerow roller bearings. The front three throws were as in a normal 6-cylinder engine, and the rear three were at 120′ to each other, No. 4 being at 1800 to No. 1, tints giving a power stroke every 60° of rotation. The throws carried double-row roller races, round which were clamped the normal big-ends of the 2-stroke-type con.-rods, which had partially cut-away little-ends. The flywheel was normal Scott and carried a Borg and Beck clutch. The crankshaft carried a thick aluminium disc outside each main bearing and these exactly fitted tunnels, one in each of five crankcase webs.

Thus the crankcase (a single alloy casting) was divided to secure crankcase compression for each cylinder, sealing being by the oil film in the roller races. The transfer passages were formed internally, with a detachable plate for the outer wall, shaped to form a venturi. Separate sleeves in which the ports were accurately machined Spigoted at their lower end into the crankcase and at their upper end into the cylinder block. The cylinder head had centrally disposed sparking plugs. Cooling was by a pump, chain-driven from the front of the crankshaft. It had vanes set at 90° to the rotor and very

effectively delivered water via an internal pipe to the area around each exhaust port. The pistons were normal Scott, with small saw cuts on the skirts to distribute oil round the cylinder bores. Lubrication was by a scavenge and a pressure pump in the sump, the former drawing oil from each crankcase chamber and returning it to the 21-gallon sump. The pressure pump forced oil to two metering pumps, one at each end of the near side of the crankcase. These pumps were driven by swash-plates from an auxiliary shaft and had six plungers. The swash-plates were controlled in conjunction with the carburetter throttle opening so that the pump stroke increased as the opening increased, metering more oil to the bearings, etc. ; the pressure pump actually supplied oil pressure, the auxiliary pumps merely controlling the sin iply. The auxiliary shaft was driven by roller chain from the front of the crankshaft, lubrication being by pressure-release from the main pump. Oil was fed to the junctions of the port sleeves and cylinders and to the cylinder bores as well as to the bearings. The engine had a safe speed of 6,600 r.p.m., limited only by the flywheel safety factor ; it weighed about 350 lb. and carburation was by two T.T. Amals.