The Mercedes-Benz M103 is a straight-6 15 degrees, crossflow cylinder head with an inclination to the right, automobile engine produced from 1984 to 1997.

It is a single overhead cam design with 2 valves per cylinder.

The CIS-E components between 2.6 and 3.0 variants are all shared for any given model year with the exception of the ECU making engine swaps from 2.6 to 3.0 virtually bolt-in.

The M 102 and M 103 engine family has a common piston stroke of 80.25 mm.

As only one decimal place is usually given, a large number of publications are in circulation with the incomplete specification of 80.2 mm.