Mercedes-Benz M180 engine


The Mercedes-Benz M180 is a family of single overhead camshaft inline-6 internal combustion engines used in Mercedes-Benz vehicles from the early 1950s to the mid‑1980s. Featuring a reverse-flow cylinder head, staggered valve arrangement, and rockers actuated by a single overhead camshaft driven by a duplex chain, these engines were produced in both carburetted and fuel‑injected versions with displacements ranging from 2.2 to 2.8 litres.
The original design is a single overhead camshaft inline-six internal combustion engine introduced at the Frankfurt Motor Show in April 1951 to power the company's new 220.
Although introduced in parallel with the M186 “big six,” that engine family is of completely different design with little or no part interchangeability. The M180, however, influenced the design of Mercedes‑Benz’s OHC four‑cylinder engine, the M121 in 1955, sharing not only the architecture but many components. It in turn influenced its diesel sibling, the OM621, in 1958. These evolved into the M115 and OM615 engines in 1968. The diesel range later expanded into the larger‑displacement OM616 in 1973 and the five‑cylinder OM617 in 1974.

2.2‑litre (M180 and M127)

M180.920

In its original form, the first‑generation M180 I had an oversquare bore and stroke, giving a 2196‑cc displacement. Fed by twin downdraught Solex 30 PAAJ carburettors and with a 6.5:1 compression ratio, it produced at 4600 rpm and at 2500 rpm, with piston speeds of 11.1 m/s and 6.1 m/s.
The engine was paired with the chassis of the Mercedes-Benz 170S to create the new W187 220 model.
  • 220 W187.011 sedan
  • 220 W187.012 Cabriolet A
  • 220 W187.013 Cabriolet B
  • 220 W187.023 coupé

    M180.921

In June 1954 the new W180 Ponton was introduced, and the engine was adapted for this car. The M180 II had a higher compression ratio and upgraded carburettors. The W180 initially appeared only as a sedan, so production of the two‑door W187 continued and also received the new engine. After the engine was upgraded to the third‑generation.924, the older motor powered the new hybrid W105 “219”, which debuted simultaneously.
It produced at 4800 rpm and at 2400 rpm.
  • 220a W180.010 sedan
  • 220 W187.023 coupé
  • 220 W187.012 Cabriolet A
  • 219 W105.010 sedan
In August 1957 the compression ratio was raised to 8.7:1. Output increased to at 4800 rpm and at 2400 rpm.
  • 219 W105.010 sedan

    M180.924

In March 1956 the 220a model was split: the hybrid W105 219 retained the second‑generation.921 engine, while the W180 was rebadged as the 220S and received the third‑generation engine. The M180 III kept the 7.6:1 compression ratio but was fed by a pair of compound Solex 32 PAJTA carburettors.
It produced at 4800 rpm and at 3500 rpm.
  • 220S W180.010 sedan
  • 220S W180.037 coupé
  • 220S W180.030 cabriolet
In August 1957 compression was raised to 8.7:1. The engine then produced at 5200 rpm and at 3500 rpm.
  • 220S W180.010 sedan
  • 220S W180.037 coupé
  • 220S W180.030 cabriolet

    M127.980

In October 1958 Bosch Mechanical fuel injection, previously limited to the exclusive W188 300S and W198 300SL, became available for the 220 series. The cars received a new chassis and model code: W128 220SE, and the engine—retaining the cylinder block—was designated the M127 I.
Fuel was delivered by a mechanically controlled multi‑point injection system operating on an intermittent group injection scheme, with two pistons controlling a group of three cylinders each. The injection pump was mechanically driven and controlled EP/ZEA 2KL 75 unit, with an injection pressure of 15 atü, equivalent to a BMEP of. Daimler‑Benz achieved this BMEP by using, in addition to manifold injection, resonance‑effect induction, giving the engine a volumetric efficiency greater than 100 per cent.
It produced at 4800 rpm and at 3800 rpm.
  • 220SE W128.010 sedan
  • 220SE W128.030 cabriolet
  • 220SE W128.037 coupé

    M180.940

In August 1959 the new W111 “Fintail” succeeded the W180 Ponton. Initially only sedans were produced. The M180 and M127 engines received performance updates.
For the W111 220b, which replaced the W105 219, the M180 IV was fed by twin Solex 34 PJCB carburettors. It produced at 4800 rpm and at 3200 rpm.
  • 220b W111.010 sedan

    M180.941

For the 220Sb, replacing the Ponton model of the same name, the M180 V initially used the enlarged compound Solex 34 PAJTA pair, but in July 1963 these were replaced with Zenith 35/40 INAT carburettors with an automatic choke.
It produced at 5000 rpm and at 3500 rpm.
  • 220Sb W111.012 sedan

    M127.982

For the 220SEb, the M127 III was updated. The two‑door W128 models still in production also received the new engine.
It produced at 4800 rpm and at 3900 rpm.
  • 220SEb W111.014 sedan
  • 220SE W128.030 cabriolet
  • 220SE W128.037 coupé

    M127.984

In its final iteration, the M127 V powered the two‑door W111 220SEb models upon their introduction in early 1961. Output was the same as for the third generation of the M127. Both the.982 and.987 would get the updated Bosch EP/ZEB 2KL 75 pump in January 1962, which improved idling control.
  • 220SEb W111.023 cabriolet
  • 220SEb W111.021 coupé

    2.3‑litre (M127 and M180)

M127.981

In summer 1963 the new‑generation W113 “Pagoda” roadster debuted. Among its novel features was a notably powerful engine. Power came from a 9.3:1 compression ratio, a Bosch PES SK 6L 70/120 R18 six‑plunger fuel‑injection pump, and a 2‑mm larger bore——increasing displacement to. The M127 II’s 127.981 code indicates that development began in 1958.
It produced at 5500 rpm and at 4200 rpm.
  • 230SL W113.042 roadster

    M180.947

In July 1965, after the introduction of the 250‑series W108, the W111 remained in production as the flagship of the Fintail sedans, now called the 230S. It was powered by the M180 VIII, which used the Pagoda’s block but the 220Sb’s cylinder head, milled to give a 9.0:1 compression ratio.
It produced at 5400 rpm and at 4000 rpm.
  • 230S W111.010 sedan

    M180.945

The lower‑priced W110 Fintail succeeded the departed 220 W111 as the 230, creating a hybrid model with a lower‑cost body and a six‑cylinder engine. The M180 IX had a 9.0:1 compression ratio and was fed by a pair of Solex 38 PDSI‑2 carburettors.
It produced at 5200 rpm and at 3600 rpm.
  • 230 W110.011 sedan

    M180.949

In July 1966 Mercedes‑Benz gave the W110 230 the same power package as the W111 230S. The M180 X now used the compound Zenith 35/40 INAT carburettor pair.
It produced at 5400 rpm and at 4000 rpm.
  • 230 W110.011 sedan

    M180.954

With the launch of the new “/8” cars in 1968, most models received redesigned engines. The exception was the W114 230, which kept the older motor, the M180 V 23. For improved reliability and cooling, the bore was reduced by 0.25 mm, decreasing displacement to, while the Zenith 35/40 INAT pair retained the automatic choke. Production continued past the 1973 facelift and ended in autumn 1976, concluding the 25‑year story of the original M180.
It produced at 5400 rpm and at 3600 rpm.
  • 230/8 W114.015 sedan
  • 230/8 W114.017 long‑wheelbase sedan
  • 230.6 W114.615 sedan
  • 230.6 W114.617 long‑wheelbase sedan

    2.5‑litre (M108 and M129)

M108.920

The introduction of the W108 in September 1965 created a new 250 series. This was achieved by stroking the 2.3‑litre M180 by 6 mm to, increasing displacement to. A change from four to seven main bearings was necessary to handle the increased power smoothly. A larger‑capacity oil pump was also fitted, and the cylinder heads had larger ports and valves enlarged by 2 mm.
The M108 I was the entry model, retaining the twin two‑barrel Zenith 35/40 INAT carburettors and 9.0:1 compression ratio of the later M180. It produced 130 hp at 5400 rpm and 19.8 kg·m at 4000 rpm.
  • 250S W108.012 sedan

    M129.980

The fuel‑injected version received the new code M129 I. A mechanically controlled six‑piston Bosch PES SK 6L 70/120 R20 six‑plunger injection pump with start and stop solenoids supplied fuel to the injectors. The injectors were repositioned for a more direct angle toward the inlet valves. The engine‑cooling fan gained six blades instead of four and incorporated a viscous coupling that engaged only when engine speed exceeded 3,000 rpm or the coolant reached a preset temperature. Initially compression was 9.3:1, but in September 1966 it was raised to 9.5:1.
It produced 150 hp at 5500 rpm and 22.0 kg·m at 4200 rpm.
  • 250SE W108.014 sedan
  • 250SE W111.023 cabriolet
  • 250SE W111.021 coupé

    M129.982

The M129 III powered the W113 Pagoda 250SL, with performance identical to the.980 version.
  • 250SL W113.043 roadster
The M129 engine proved controversial and short‑lived. Although the crankshaft had seven bearings, the cylinders were still asymmetrically spaced in pairs, causing uneven cooling between each pair. This was not a problem in the 2.3‑litre M127, but the stroked motor’s peak piston speed rose to 14.4 m/s, creating excessive stress and leading to premature failures. To address this, Mercedes‑Benz redesigned the cylinder block with symmetrical cylinder bores, resulting in two new engines: the M114 for the 2.5‑litre displacement and a bored‑out M130.

2.5‑litre (M114)

M114.920

The M114 V 25 was the smaller‑displacement version of the redesigned cylinder block with symmetrical cylinder spacing, retaining the connecting rods and pistons of the M108. It also kept the Zenith carburettors and 9.0:1 compression. It was offered in the flagship 250 model of the new “/8” series.
It produced 130 hp at 5400 rpm and 20.3 kg·m at 3600 rpm.
  • 250/8 W114.010 sedan
  • 250C W114.021 coupé