From Mercedes Wiki

The M123 engine family was a Straight-6 automobile engine from Mercedes-Benz in the 1970s and 1980s.

M123.920

The M123.920 was a 2.5 L (2525 cc) engine with an 86 mm bore and 72.45 mm stroke. Power output was 129 hp (96 kW).

Applications:

• 1976-1979 250
• 1976-1979 250 Long
• 1976-1979 250T

M123.921

The revised M123.921 was also 2.5 L (2525 cc) engine. Power output was 140 hp (104 kW).

Applications:

• 1979-1985 250
• 1979-1985 250 Long
• 1979-1985 250T

See also

• List of Mercedes-Benz engines

280S engine