Double Engine

A U engine is a piston engine made up of two separate straight engines (complete with separate crankshafts) joined by gears or chains. It is similar to the H engine which couples two flat engines. The design is also sometimes described as a "twin bank" or "double bank" engine, although these terms are sometimes used also to describe V engines.

This configuration is uncommon, as it is heavier than a V design. The main interest in this design is its ability to share common parts with straight engines. However, V engines with offset banks can also share straight engine parts (except for the crankshaft), and this is therefore a far more common design today when both engine forms are produced from the same basic design.