pair of cylinders on this air-cooled engine were prone to overheating. The 1985-1987 Suzuki RG500 motorcycle, and several related racing motorcycles, used a water-cooled four-cylinder U engine. Although some racing success was achieved, the road bikes did not sell well and the design was phased out in favour of a conventional inline-four engine. Diesel In the 1930s Sulzer Brothers Ltd. began production of an 'LD series' twelve-cylinder U engine for use in rail locomotives. The LD series was replaced by the LDA series, for a combined production period of over 50 years. The Sulzer 12LDA twin-bank engine formed the mainstay of British locomotives built in the 1960s, with over 700 used in the Peak and Class 47 locomotives. The Sulzer LDA engine used a smaller gear for the central output shaft than the two gears attached to the crankshaft. This resulted in the output shaft rotating at approximately 1000 rpm while the crankshafts rotated at approximately 750 rpm. The purpose of this gearing was to allow the use of a smaller, and lighter, electrical generator when the engine was used in a diesel-electric locomotive. The General Motors 6046 is a twin-engine setup that was used by Sherman tanks during World War II. The 6046 was built using two straight-six engines that were separately clutched to a single output shaft, which was itself clutched to the transmission unit. A total of 10,968 6046D-powered M4A2 Shermans were produced. After World War II, several Soviet Union tanks powered by 16-cylinder and 18-cylinder engines that were reverse-engineered from the General Motors 6046 engine. These Soviet engines were designated Russkiy Dizel (Diesel Energo) DPN23/2H30 and the DRPN23/2H30. Variations Tandem twin engine A tandem twin engine, occasionally used in motorcycles and go-karts, is a two-cylinder engine which uses a similar design to U engines. The motor has two crankshafts, one for each cylinder which are joined and kept in co-ordination by load carrying, crank-phasing gears connecting the two cylinders. The tandem twin layout is used only with two-stroke engines since these must have a discrete crankcase chamber per cylinder. The prime advantage of a tandem-twin two-stroke is that the engine can be very narrow while allowing chain final drive without a power-wasting 90° turn. Between 1975 and 1982, Kawasaki used the design to win four 250 cc and four 350 cc world championships before they retired from Grand Prix racing. The engine design was also used