Twingle engine

The Twingle engine is a small-capacity two-stroke petrol engine. It uses two pistons, one of which controls the inlet ports, the other the exhaust ports. These run in two parallel cylinder bores but share a single combustion chamber, spark plug and cylinder head.

The first Twingle engine was designed by Alberto Garelli, who patented the design in 1912. His design had a forked connecting rod with two small-ends and one big-end, and had a capacity of 346 cc. Garelli produced some motorcycles with this engine, but was more successful with more conventional designs.

Two versions of the Twingle engine were produced by Austrian moped manufacturer Puch. The earlier, based on the Garelli design, was produced from 1923. From 1949 this was replaced by a design by Giovanni Marcellino, with different sized pistons and a more elaborate connecting-rod setup. The Marcellino engine continued in production until 1970. It was complex and expensive to produce compared to a conventional single cylinder engine, and heavier for the same power output. Its only advantage was claimed to be fuel efficiency.

Both the Garelli and Marcellino engines are sometimes described as two-cylinder and sometimes as one-cylinder. Possibly as a result, the Twingle is sometimes confused with the opposed piston two-stroke diesel engine design, which has two pistons per cylinder at opposite ends of the cylinder, and no cylinder head at all. Like the Twingle, the opposed piston design uses one piston to control the inlet ports and another the exhaust, but there the similarity ends.

It is easy to see how a Twingle engine could be mistaken for a single cylinder engine. It looks, sounds and in most ways performs like one, and has only one spark plug, but in fact the Twingle has two pistons each in its own separate cylinder bore.