This is a famous engine and will be remembered by many as the engine which powered the famous DH Tiger Moth, the aircraft which thousands of RAF pilots trained on. The engine is a four-cylinder, inverted, air-cooled, direct-drive type, with a bore of 118mm stroke 140mm and capacity of 6124cc compression ration 5.25:1, weight complete 306lbs, 2,000rpm approximately (cruising) petrol consumption 9 gallons per hour.
Modern ‘in line’ engines are of the inverted type, an arrangement which gives an excellent forward field of vision for the pilot and enables the cooling of the cylinders to be effected satisfactorily, also the greater bulk of the engine (the cylinders and the lower half of the crankcase) is located below the propeller axis.
Lubrication is of the dry sump type; briefly, oil is contained in a tank remote from the engine, and is pumped to the crankshaft, then by suitably placed escape holes, the rest of the engine i.e. cylinder walls and pistons are lubricated. By careful design the oil is then drained down to a scavenging pump and returned through an oil cooler back to the oil tank.