Mercedes-Benz M121 engine
The Mercedes-Benz M121 engine was a single overhead camshaft inline four-cylinder engine used by Mercedes-Benz in 1955 in various model lines during the 1950s and 1960s. Based off of the M180 engine|M180] six cylinder engine, introduced three years prior, it replaced the OHV M136 engine|M136] motor, that was in production since 1935.
The engine's first application was in the W121 Mercedes 190SL luxury roadster in May of 1955, built until Februarly 1962. After 1956 and until the close of 1967 it would power the entry level 180, 190 and 200 series of the W120, W121 and W110 sedans.
It 1958 a diesel version, OM621 engine|OM621] would be produced alongside, sharing many of the components. In 1968 the engine would modernised into the M115 engine|M115], which would power the W115 and later the W123 sedans, and the W460 G-wagen, until it's retirement in 1985. The diesel counterpart, the OM615 engine|OM615] would also be produced until 1985. In 1973 a larger displacement 2.3 litre OM616 engine|OM616] will join the lineup, and in 1974 a five cylinder OM617 engine|OM617] will follow.
In addition and trucks such as the Unimog and L319 models. The M121 series was in production until 1967, when the M115 engine took its place.
History
The M121 engine was developed just after the end of World War II. It was built in the Sindelfingen Works factory, which assembled the Mercedes Ponton Model series to which the engine belonged to. The M121 engine made its debut in 1955. It was the first generation of 4-cylinder engines from Mercedes Benz. The M121 replaced the less efficient M136 1.8-litre engine, a pre World War II engine that was introduced 2 years before in 1953. The M121 benefited from innovations and technology from Mercedes' larger engines such as the M186 engine|M186] 3.0-litre and M180 2.2 liter engines. One of these innovations was a new single over head camshaft design which allowed for more power and efficiency. It was developed by a team led by Hans Scherenberg. Within this team, Karl-Heinz Goschel was one of the key engineers who developed the engine design.M121 variants
M121
The M121 engine featured a single chain driven overhead camshaft layout with staggered valves operated by long and short rocker arms. The cylinder block was made from cast iron. The cylinder bore diameter for the M121 was. The three ring crankshaft was forged. The stroke of the engine was. This gave the M121 a displacement of. The engine had a compression of 8.5:1 and a single exhaust. Through this configuration, the M121 BII engine had an initial rating of at 5500 RPM and of torque at 4000 rpm. After testing of the final vehicle, the power rating was lowered to. The crankshaft was initially carried by three main bearings, raised to five in the M121 BIX variant.Image:190 SL Motor.jpg|thumb|M121 engine in a 190SL
Image:W110 M121 Motor.JPG|thumb|M121 engine 4-Cyl. 1.9 litres / in a 1964 W110 190c