Boxer Engine (Flat Engine)

The flat layout gives a low centre of gravity, which helps handling and lets the bonnet sit lower. Opposed pistons cancel many of each other's vibrations, so a flat-four or flat-six runs smoothly without balance shafts. The engine is wide, which can make spark plugs, gaskets and some other parts harder to reach than on an inline engine.

Two banks of cylinders lie flat on either side of a central crankshaft, with each opposed pair of pistons moving outwards and inwards at the same time.

Oil leaks from valve cover and head gaskets on the low-mounted cylinder heads are a common workshop job. Some jobs, such as changing spark plugs, can take longer than on an upright engine.