U engine

[3] The Fiat 806 was a 1927 Grand Prix racing car that was powered by a 1.5 L (92 cu in) twelve-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.

[citation needed] In the 1930s Sulzer Brothers Ltd. began production of an 'LD series' twelve-cylinder U engine for use in rail locomotives.

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.

[16] 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.

[20] Rotax developed a similar tandem twin design, the model 256, which it sold to independent constructors.

The CCM Armstrong 250 cc, Waddon, EMC, Hejira, Decorite, and Cotton racers used this engine.

[22] An unusual variation on the U engine is the use of a single crankshaft which is linked to the pistons in both cylinder banks by rocking beams.