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The BMW 247 engine is an air-cooled flat-twin motorcycle engine with two valves per cylinder, also known as "airhead" boxer. The 247 engine was the successor of the in 1969 (MY 1970) introduced first modern BMW boxer engine; the BMW 246 engine of the /5 series. With minor and more significant updates (247/76 in 1976 and 247/M80 in 1981) it was ...
The Type 247 Engine was used with smaller pistons, carburetors and a different final drive to assist acceleration. For the German market, the 473cc R45 came with a reduced power output of 27 BHP (@to qualify for favorable insurance) while versions sold elsewhere had 35 BHP on tap.
The 247 cc engine was a higher performance development of that used the existing C15. Bore and stroke of 67 x 70 mm was retained, [6] but a new alloy barrel and cylinder head were introduced featuring square fins. [7] [8] The pushrod tunnel was cast into the barrel rather than being a separate item as on earlier models.
Based largely on the R26, in 1960 the R27 added rubber mounts for the engine and boosted power to 18 hp (13 kW). The 250 cc OHV vertical single was the only rubber-mounted thumper engine BMW ever produced, and was their last shaft drive single-cylinder motorcycle. The engine pumped out 18 hp (13 kW), the highest ever for a shaft-drive BMW single.
The 247 could fly on one engine. With controllable-pitch propellers, the 247 could maintain 11,500 ft (3,500 m) at maximum gross weight on one engine. [9] Aside from its size, much lower wing loading, and the wing spar obstructing the cabin, many of its features became the norm for airliners, including the Douglas DC-1, before World War II. [6]
United Airlines had exclusive right to the all metal twin-engine Boeing 247; rival TWA issued a specification for an all-metal trimotor. The Douglas response was more radical. When it flew on July 1, 1933, the prototype DC-1 had a robust tapered wing, retractable landing gear, and two 690 hp (515 kW) Wright radial engines driving variable-pitch ...
Most airheads made from 1969 to 1995 used the BMW 247 engine, although 248/1 engines were used on mid-sized R-series motorcycles from 1978 to 1993. Even high-performance motorcycles, such as the R90S used the 247 engine; and its successor, the R100RS, was fitted with an oil cooler.
Ram Air engine. The T250's engine was a development of the earlier T20, which had been introduced in 1966. The 180° piston ported two stroke twin was of unit construction and had alloy head and alloy barrels with cast iron liners. Bore and stroke were 54 mm × 54 mm (2.1 in × 2.1 in) and the claimed power output was 31 bhp (23 kW) @ 7,000 rpm.