Mercedes-Benz M180 engine
The Mercedes Benz M180 Engine was a 2.2 litre (134ci) single overhead camshaft inline-6 cylinder engine introduced at the Frankfurt Motor show in April 1951 to power the company's new 220 (W187). It was the first engine with a cylinder bore greater than its stroke that Mercedes had installed in a production car
It spawned four variants through 1968, the final and largest being the 2.8 L M130. It was achieved by boring out and stroking the M180's original "over-square" 80mm bore × 72.8mm stroke 2.2 L to 86.5mm × 78.8mm, yielding a displacement of 2,778 cc/170ci.
While sharing many design features such as staggered valve arrangement and rockers running off a single overhead camshaft driven by a duplex cam-chain, the engines were of completely different design with little or no inter-changeability of parts.
The original M180 engine was rated at 80 hp (60 kW). It powered the W187 220 sedan, coupé, and cabriolet (Type A and B) from 1951 to 1955, the W180 220a sedan, coupé, and cabriolet from 1954 to 1956 and the W105 219 4-door sedan from 1956 to 1959.
It also powered the MB Unimog 404s, the military all-round vehicle: It was built from 1955 until 1980.
It was used as a "Pritsche", for towing light guns and carrying their crew, as ambulance, Radio vehicle, Fire vehicle, especially at airports and airbases.
Other Unimogs, agricultural used, used already OM-type engines (Öl Motor, or Diesel engine) but in the given period it should be more save, logistic reliable to use petrol engines for the military.
The W180 Ponton 220S Sedan, Coupe and Cabriolet of 1956-1959 benefited from the up-rated M180.924 which delivered 124 hp (92 kW). In 1958 Bosch mechanical fuel injection was added to the 2.2 litre six and the engine, now giving 113-134 hp, was redesignated M127. The M127 was fitted to the last of the Pontons: the rare 1958 W128 220SE, of which fewer than 4000 were produced.
In 1959 the first series of W111 "Fintail" 220SE and 220SEb models was introduced, with the carburetted M180 in the 220b and 220Sb and the M127 used in the 220SEb. The addition of the lower case ‘b’ was added to differentiate the Fintails from the earlier Pontons.
In 1965 the W111/W112 sedans were superseded by the new W108/109 series 230 and 230S (apart from the W111 230/230S, produced from 1965 to 1968 to use up the old fintail bodyshells). The M180 was bored by 2 mm, creating a 82mm bore × 72.8mm stroke and displacement of 2,307 cc/141ci). All models received the new 2.3 L engine.
The M180's stroke was increased to produce the 2.5 L engine for the new Mercedes-Benz W108 250S and 250SE. A 6 mm increase resulted in an 82mm bore × 78.8mm stroke and displacement of 2,496 cc/152ci), carburetted on the 250S and fuel-injected on the 250SE, designated the M129. The M129 was fitted with a mechanically controlled six-piston fuel injection pump. A change from four to seven main bearings was necessary in order smoothly to handle the resulting increase in power. A larger capacity oil pump was also specified. Connecting rods were slightly shortened, reflecting the 6mm longer stroke in a block of unchanged overall height. The redesigned cylinder heads incorporated larger ports, and the valve diameters were increased by 2mm. On the fuel injected cars a six-plunger pump replaced the previous car's two plunger pump and the injectors were repositioned to give a more direct angle towards the inlet valve heads. The engine cooling fan now had six blades instead of four and incorporated a viscous coupling which activated the fan only when engine speed exceeded 3,000 rpm or the radiator water temperature reached a preset limit. I think engine of 250 S was called M108 (for W108 chassis) and only 250 SE engine was designated M129.
In 1968 the ‘New Generation’ or /8 models were introduced, along with a change to the venerable mid-size six. The M180 engine of the 230/230S was continued in the W114 230 and 230.6, while the M180 of the 250S underwent a few changes and was renamed the M114. This was also available with Bosch D-Jet fuel injection, as fitted to the 250CE. The M129 of the 250SE were superseded by the M130, the ultimate variant of the mid-sized six, obtained by increasing the 2.5-litre versions' bore by 4.5 mm using the same stroke (86.5mm bore × 78.8mm stroke → 2,778 cc/170ci). This was the maximum practical enlargement of the engine given the limitations of the block as evidenced by the deletion of water passages between the cylinders. It was used in the 280S and 280SE.
The M186 'Big six' was discontinued at this time, and the 1968-1971 300SE/300SEL used the same M130 as the 280SE and 280 SL.
Mid-sized six-cylinder head design
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The mid-sized six carries over the 1951 190SL's four-cylinder SOHC general design, with non-cross-flow (reverse-flow) ports all located on one side of the head casting.
The combustion chamber design is very similar to the pre-WW2 Chevrolet "Blue Flame" OHV six-cylinder, with a "dog leg" L-shaped chamber. The exhaust valve is deeply recessed in a pocket containing most of the chamber volume, and the much longer intake valve is nearly flush with the deck surface. This design of inlet tract, with the large valve opening directly into the cylinder from an individual, semi-downdraught port, provides excellent gas flow resulting in the high volumetric efficiencies of these engines (157 and 158 BMEP from the 2.2L and 2.8L fuel injected versions)
- Six Appeal, Mercedes Enthusiast, May 2007, pp 52-58