Mercedes-Benz M121 engine
{{Infobox automobile engine
| name = Mercedes-Benz M121
| image = M121 Judson supercharger.jpg
| manufacturer = Mercedes-Benz
| production = 1955-1967
| configuration = inline 4
| valvetrain = SOHC 2 valves x cyl.
| compression = 8.5:1, 9.0:1
| block = Cast iron
| fueltype = Gasoline
| fuelsystem = Twin parallel Solex 38PDSJ carburetors
| coolingsystem = Water cooled
| predecessor = M136
| successor = M115
| displacement = {{ubl|{{convert|1897|cc|L|1|abbr=on|disp=flip}}|{{convert|1988|cc|L|1|abbr=on|disp=flip}}}}
| bore = {{ubl|{{convert|85|mm|2|abbr=on}}|{{convert|87|mm|2|abbr=on}}}}
| stroke = {{convert|83.6|mm|2|abbr=on}}
| power = {{convert|75-110|hp|kW PS|0|abbr=on}}
| torque = {{convert|154|Nm|lbft|0|abbr=on}}
}}
The Mercedes-Benz M121 engine was a 1.9 liter single overhead camshaft inline four-cylinder engine introduced by Mercedes in 1955 and used in various model lines during the 1950s and 1960s. Rated at {{convert|56|kW|PS hp|0|abbr=on}} at 5500 rpm in its base version, it replaced the 1.8 liter M136 introduced in 1935, offering improved performance over the M136's side camshaft design. The engine's first application was in the W121 Mercedes 190SL luxury roadster in May of 1955, in a high-performance {{convert|105|hp|kW PS|0|abbr=on}} M121 BII version.
Applications included mid-size sedans, such as the 190, the 190SL roadster, 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.[http://www.mbzponton.org/valueadded/other/overview.htm/ "Historical Perspective"] {{webarchive|url=https://web.archive.org/web/20101229093713/http://mbzponton.org/valueadded/other/overview.htm |date=2010-12-29 }}, Mercedes Benz Ponton, Retrieved on 11-22-2010. 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 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 {{convert|85|mm|2|abbr=on}}. The three ring crankshaft was forged. The stroke of the engine was {{convert|83.6|mm|2|abbr=on}}. This gave the M121 a displacement of {{convert|1897|cc|L|1|abbr=on|disp=flip}}. The engine had a compression of 8.5:1 and a single exhaust.[http://auto.howstuffworks.com/1955-1963-mercedes-benz-190sl3.htm "1955-1963 Mercedes-Benz 190SL"], How Stuff Works, September 18, 2007. Retrieved on 11-22-2010. Through this configuration, the M121 BII engine had an initial rating of {{convert|110|hp|kW PS|0|abbr=on}} at 5500 RPM and {{convert|114|lbft|0|abbr=on}} of torque at 4000 rpm. After testing of the final vehicle, the power rating was lowered to {{convert|105|hp|kW PS|0|abbr=on}}. The crankshaft was initially carried by three main bearings, raised to five in the M121 BIX variant.
Image:W110 M121 Motor.JPG 190c]]
=M121 BI=
The M121 BI was developed for the new W110 190c introduced in 1961. It had an increase of {{convert|5|hp|kW PS|0|abbr=on}}, yet retained the same fuel consumption ({{convert|11.5|L/100 km|abbr=on}} on premium gasoline). Top speed increased to {{convert|150|km/h|abbr=on}} from {{convert|139|km/h|abbr=on}}. Both performance increases were achieved despite the new model's significantly heavier bodywork{{how|reason=How did hp and mileage go up - what was changed in the engine? It is never explained.|date=March 2025}} required to meet new safety regulations.
=M121 BII=
The first version of the M121 to reach the market, the M121 BII was put into serial production in May of 1955 for use in the new W121 Mercedes 190SL roadster.[https://mercedes-benz-publicarchive.com/marsClassic/en/instance/ko/190-SL-Roadster--W-121-B-II-1955---1963.xhtml?oid=4657&ls=L3NlYXJjaHJlc3VsdC9zZWFyY2hyZXN1bHQueGh0bWw_c2VhcmNoU3RyaW5nPTE5MCtzbCZzZWFyY2hJZD0wJnNlYXJjaFR5cGU9ZGV0YWlsZWQmcmVzdWx0SW5mb1R5cGVJZD0yMTU1JnRodW1iU2NhbGVJbmRleD0xJnJvd0NvdW50c0luZGV4PTUmdmlld1R5cGU9bGlzdCZzb3J0RGVmaW5pdGlvbj1TT1JULTE!&rs=1 190 SL Roadster], Mercedes-Benz Archive[http://www.mbzponton.org/valueadded/technical/techgas.html "Mercedes-Benz Ponton Technical Data"]{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }}, Mercedes-Benz Ponton, Retrieved on 2010-10-27. Fitted with dual carburetors, it produced {{convert|105|hp|kW PS|0|abbr=on}} at 5700 rpm. For the 190SL, acceleration to {{convert|100|km/h|abbr=on}} took 14.5 seconds, and the top speed was {{convert|180|km/h|mph|abbr=on}}. This made the M121 BII one of the faster engines on the road in its day.{{cn|date=December 2022}} The fuel economy of the M121 BII was {{convert|8.6|L/100 km|abbr=on}}.
=M121 BIX=
The final version of the M121 engine was the 2.0 L M121BIX, produced from 1965 to 1968 for the new W110 Mercedes Benz 200. A {{convert|2|mm|abbr=on}} increase in bore from {{convert|85|to|87|mm|2|abbr=on}} enlarged displacement to {{convert|1897|to|1988|cc|L|1|abbr=on|disp=flip}}. Compression was increased to 9.0:1, the crankshaft went from three to five bearings, and a second Solex 38PDSJ carburetor was added.[https://mercedes-benz-publicarchive.com/marsClassic/en/instance/ko/Fintail-Mercedes-four-cylinder-models-W-110-1961---1968.xhtml?oid=5111#:~:text=This%20engine%20was%20a%20detuned,in%20top%20speed%20and%20acceleration "Fintail Mercedes", four-cylinder models (W 110), 1961 - 1968], Mercedes-Benz Archive Combined, power was increased to {{convert|95|hp|kW PS|0|abbr=on}} at 5200 rpm and {{convert|154|Nm|lbft|0|abbr=on}} of torque was produced at 3600 rpm.
Applications
The M121 engine was first employed in the 1956 Mercedes Benz W121 180 "Ponton". The subsequent 190 and 200 models featured an updated version which offered greater performance through variations in compression ratios and improved carburetor systems. Its use continued in the W110 "Fintail" 190c and 200. The M121 engine has also been used in trucks such as the Mercedes-Benz L319 introduced in 1967. 1967. Some Unimog off-road models also used the M121.
References
Hodzic, Muamer. [http://www.benzinsider.com/2008/06/mercedes-benz-gasoline-engines-since-1945/ "Mercedes-Benz gasoline engines since 1945 "], Mercedes Insider, June 24, 2008. Retrieved on 11-22-2010.[http://www.seriouswheels.com/cars/1950-1959/top-1955-1963-Mercedes-Benz-190-SL.htm "1955-1963 Mercedes-Benz 190SL"] {{Webarchive|url=https://web.archive.org/web/20100524133709/http://seriouswheels.com/cars/1950-1959/top-1955-1963-Mercedes-Benz-190-SL.htm |date=2010-05-24 }}, Serious Wheels, Retrieved on 11-22-2010.[http://www.emercedesbenz.com/Mar08/25_001082_Winning_Foursomes_A_Look_At_Mercedes_Four_Cylinder_Engines.html Winning Foursomes] {{Webarchive|url=https://web.archive.org/web/20110111063151/http://www.emercedesbenz.com/Mar08/25_001082_Winning_Foursomes_A_Look_At_Mercedes_Four_Cylinder_Engines.html |date=2011-01-11 }}, eMercedesBenz, March 25, 2008. Retrieved on 11-22-2010.