The Mercedes-Benz M180 (along with the related M127, M108, M129, M130, M114, and M123) is a family of single overhead camshaft inline-6 internal combustion engines used in Mercedes-Benz vehicles from the early 1950s to the midâÂÂ1980s. 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 fuelâÂÂinjected 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 (W187).
Although introduced in parallel with the M186 âÂÂbig six,â that engine family (M188, M189, M194, M198, M199) is of completely different design with little or no part interchangeability. The M180, however, influenced the design of MercedesâÂÂBenzâÂÂs OHC fourâÂÂcylinder 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 largerâÂÂdisplacement OM616 in 1973 and the fiveâÂÂcylinder OM617 in 1974.
In its original form, the firstâÂÂgeneration M180 I (180.920) had an oversquare bore and stroke, giving a 2196âÂÂcc displacement. Fed by twin downdraught Solex 30 PAAJ carburettors and with a 6.5:1 compression ratio, it produced at 4600â¯rpm and at 2500â¯rpm, with piston speeds of 11.1â¯m/s (maximum) and 6.1â¯m/s (mean).
The engine was paired with the chassis of the Mercedes-Benz 170S to create the new W187 220 model.
In June 1954 the new W180 Ponton was introduced, and the engine was adapted for this car. The M180 II (180.921) had a higher compression ratio (7.6:1) and upgraded carburettors (Solex 32 PAATJ). The W180 initially appeared only as a sedan , so production of the twoâÂÂdoor W187 continued and also received the new engine. After the engine was upgraded to the thirdâÂÂgeneration .924 (see below), the older motor powered the new hybrid W105 âÂÂ219âÂÂ, which debuted simultaneously.
It produced at 4800â¯rpm and at 2400â¯rpm (piston speeds 11.6â¯m/s max, 5.8â¯m/s mean).
In August 1957 the compression ratio was raised to 8.7:1. Output increased to at 4800â¯rpm and at 2400â¯rpm (piston speeds 11.6â¯m/s max, 5.8â¯m/s mean).
In March 1956 the 220a (W180) model was split: the hybrid W105 219 retained the secondâÂÂgeneration .921 engine (see above), while the W180 was rebadged as the 220S and received the thirdâÂÂgeneration engine. The M180 III (180.924) kept the 7.6:1 compression ratio but was fed by a pair of compound Solex 32 PAJTA carburettors.
It produced at 4800â¯rpm and at 3500â¯rpm (piston speeds 11.6â¯m/s max, 8.5â¯m/s mean).
In August 1957 compression was raised to 8.7:1. The engine then produced at 5200â¯rpm and at 3500â¯rpm (piston speeds 12.6â¯m/s max, 8.5â¯m/s mean).
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 engineâÂÂretaining the cylinder blockâÂÂwas designated the M127 I (127.980).
Fuel was delivered by a mechanically controlled multiâÂÂpoint 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 15â¯atü (about 1570â¯kPa), equivalent to a BMEP of . DaimlerâÂÂBenz achieved this BMEP by using, in addition to manifold injection, resonanceâÂÂeffect induction, giving the engine a volumetric efficiency greater than 100â¯per cent.
It produced at 4800â¯rpm and at 3800â¯rpm (piston speeds 11.6â¯m/s max, 9.2â¯m/s mean).
In August 1959 the new W111 âÂÂFintailâ 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 (180.940) was fed by twin Solex 34 PJCB carburettors. It produced at 4800â¯rpm and at 3200â¯rpm (piston speeds 11.6â¯m/s max, 7.8â¯m/s mean).
For the 220Sb, replacing the Ponton model of the same name, the M180 V (180.941) 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 5000â¯rpm and at 3500â¯rpm (piston speeds 12.1â¯m/s max, 8.5â¯m/s mean).
For the 220SEb (the lowerâÂÂcase âÂÂbâ distinguishing it from the Ponton sedan it replaced), the M127 III (127.982) was updated. The twoâÂÂdoor W128 models still in production also received the new engine.
It produced at 4800â¯rpm and at 3900â¯rpm (piston speeds 11.6â¯m/s max, 9.5â¯m/s mean).
In its final iteration, the M127 V (127.984) powered the twoâÂÂdoor 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.
In summer 1963 the newâÂÂgeneration W113 âÂÂPagodaâ 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 sixâÂÂplunger fuelâÂÂinjection pump, and a 2âÂÂmm larger boreâÂÂâÂÂincreasing displacement to . The M127 IIâÂÂs 127.981 code indicates that development began in 1958.
It produced at 5500â¯rpm and at 4200â¯rpm (piston speeds 13.3â¯m/s max, 10.2â¯m/s mean).
In July 1965, after the introduction of the 250âÂÂseries W108, the W111 remained in production as the flagship of the Fintail sedans, now called the 230S. It was powered by the M180 VIII (180.947), which used the PagodaâÂÂs block but the 220SbâÂÂs cylinder head, milled to give a 9.0:1 compression ratio.
It produced at 5400â¯rpm and at 4000â¯rpm (piston speeds 13.1â¯m/s max, 9.7â¯m/s mean).
The lowerâÂÂpriced W110 Fintail succeeded the departed 220 W111 as the 230, creating a hybrid model with a lowerâÂÂcost body and a sixâÂÂcylinder engine (similar to the W105 219). The M180 IX (180.945) had a 9.0:1 compression ratio and was fed by a pair of Solex 38 PDSIâÂÂ2 carburettors.
It produced at 5200â¯rpm and at 3600â¯rpm (piston speeds 12.6â¯m/s max, 8.7â¯m/s mean).
In July 1966 MercedesâÂÂBenz gave the W110 230 the same power package as the W111 230S. The M180 X (180.949) now used the compound Zenith 35/40 INAT carburettor pair.
It produced at 5400â¯rpm and at 4000â¯rpm (piston speeds 13.1â¯m/s max, 9.7â¯m/s mean).
With the launch of the new âÂÂ/8â cars in 1968, most models received redesigned engines (the M114 and its fourâÂÂcylinder counterpart, the M115). The exception was the W114 230, which kept the older motor, the M180 V 23 (180.954). For improved reliability and cooling, the bore was reduced by 0.25â¯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 25âÂÂyear story of the original M180.
It produced at 5400â¯rpm and at 3600â¯rpm (piston speeds 13.1â¯m/s max, 8.7â¯m/s mean).
The introduction of the W108 in September 1965 created a new 250 series. This was achieved by stroking the 2.3âÂÂlitre M180 by 6â¯mm to , increasing displacement to . A change from four to seven main bearings was necessary to handle the increased power smoothly. A largerâÂÂcapacity oil pump was also fitted, and the cylinder heads had larger ports and valves enlarged by 2â¯mm.
The M108 I (108.920) was the entry model, retaining the twin twoâÂÂbarrel Zenith 35/40 INAT carburettors and 9.0:1 compression ratio of the later M180 (.941). It produced 130â¯hp (96â¯kW) at 5400â¯rpm and 19.8â¯kg÷m (194â¯N÷m) at 4000â¯rpm (piston speeds 14.1â¯m/s max, 10.5â¯m/s mean).
The fuelâÂÂinjected version received the new code M129 I (129.980). A mechanically controlled sixâÂÂpiston Bosch PES SK 6L 70/120 R20 sixâÂÂplunger 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 engineâÂÂcooling fan gained six blades instead of four and incorporated a viscous coupling that engaged only when engine speed exceeded 3,000â¯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 150â¯hp (110â¯kW) at 5500â¯rpm and 22.0â¯kg÷m (216â¯N÷m) at 4200â¯rpm (piston speeds 14.4â¯m/s max, 11.0â¯m/s mean).
The M129 III (129.982) powered the W113 Pagoda 250SL, with performance identical to the .980 version.
The M129 engine proved controversial and shortâÂÂlived. 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 2.3âÂÂlitre M127, but the stroked motorâÂÂs peak piston speed rose to 14.4â¯m/s (versus 13.1â¯m/s for the 2.3), creating excessive stress and leading to premature failures. To address this, MercedesâÂÂBenz redesigned the cylinder block with symmetrical cylinder bores, resulting in two new engines: the M114 for the 2.5âÂÂlitre displacement and a boredâÂÂout M130 (see below).
The M114 V 25 (114.920) was the smallerâÂÂdisplacement 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 âÂÂ/8â series.
It produced 130â¯hp (96â¯kW) at 5400â¯rpm and 20.3â¯kg÷m (199â¯N÷m) at 3600â¯rpm (piston speeds 14.1â¯m/s max, 9.5â¯m/s mean).
In late 1968 MercedesâÂÂBenz introduced the twoâÂÂdoor W114 coupé. Alongside the .920 engine for the 250C, a sister 250CE model was released with the M114 E 25 (114.980), featuring the new electronically controlled Bosch DâÂÂJetronic systemâÂÂthe first MercedesâÂÂBenz engine to receive this technology.
It produced 150â¯hp (110â¯kW) at 5500â¯rpm and 21.5â¯kg÷m (211â¯N÷m) at 4500â¯rpm (piston speeds 14.4â¯m/s max, 11.8â¯m/s mean).
The M114 was replaced by the largerâÂÂbore M130 in May 1972.
The symmetrical cylinder block of the M114 allowed for another displacement increase. The bore was enlarged by 4.5â¯mm to , resulting in a displacementâÂÂthe maximum feasible for this block.
The carburetted version, the M130 V 28 (130.920) with 9.0:1 compression, was installed in the 280S for the 1968 model year.
It was later replaced by the carburetted M110 DOHC engine in the W116 SâÂÂClass.
The M130 E 28 (130.980) was the fuelâÂÂinjected version that superseded the M129 in the W108 sedans and W111 coupés and cabriolets.
It produced 160â¯hp (118â¯kW) at 5500â¯rpm and 24.5â¯kg÷m (240â¯N÷m) at 4250â¯rpm (piston speeds 14.4â¯m/s max, 11.2â¯m/s mean).
It was replaced by the fuelâÂÂinjected DOHC M110 engine in the SâÂÂClass.
In parallel with solving the M108/M129 asymmetry issue, MercedesâÂÂBenz also retired the âÂÂbig sixâ M189 engine that still powered the flagship 300 series.
The M130 E 28 (130.981) was slightly more powerful, producing 170â¯hp (125â¯kW) at 5750â¯rpm and 24.5â¯kg÷m (240â¯N÷m) at 4500â¯rpm.
Production ended after the introduction of the M116 V8 in the 300SEL 3.5, which better suited the price expectations of customers for the airâÂÂsuspended W109.
The W113 Pagoda received the M130 E 28 (130.983) with more aggressive camshaft profiles.
It also produced 170â¯hp (125â¯kW) at 5750â¯rpm and 24.5â¯kg÷m (240â¯N÷m) at 4500â¯rpm (piston speeds 15.1â¯m/s max, 11.8â¯m/s mean).
It was replaced by the M110âÂÂpowered R107 280SL.
When the W114 coupé was launched, exporting it to markets with newly introduced emission controls posed bureaucratic hurdles. To compensate for power loss, for the 1969 model year the U.S.âÂÂdestined 250C was sold with the larger M130 engine. A year later, the 250 sedan for the 1970 model year also received the 2.8âÂÂlitre motor.
In April 1972, after the W108 was retired, MercedesâÂÂBenz made the M130âÂÂpowered W114 available on the home market. To avoid confusion with the M110âÂÂpowered 280 and 280C models that appeared simultaneously, the company kept the 250 badge and retired the M114 due to redundancy.
The M130 V 28 (130.923) had a lower 8.7:1 compression ratio. It produced 130â¯hp (96â¯kW) at 5000â¯rpm and 22â¯kg÷m (216â¯N÷m) at 3200â¯rpm (piston speeds 13.1â¯m/s max, 8.4â¯m/s mean).
It was replaced by the M123 engine in the W123 250 sedan . The W114 250C coupé did not receive a direct successor; instead, the C123 offered an entryâÂÂlevel 230C model with the M115 fourâÂÂcylinder engine.
In 1975, with the launch of the W123, MercedesâÂÂBenz rationalised its sixâÂÂcylinder range. At that time the lineup included the veteran M180 in the 230.6, the 2.8âÂÂlitre M130 in the 250, and the flagship 280 and 280E with the 2.7âÂÂlitre M110.
Most 230.6 models were sold to commercial fleet customers. Shifting purchasing trends after the 1973 oil crisis reduced demand for the 250 series. Meanwhile, demand for M110âÂÂpowered vehiclesâÂÂespecially in the W116 SâÂÂClass and the SL and SLC twoâÂÂdoor modelsâÂÂexceeded expectations, as customers chose these more economical entryâÂÂlevel models over their V8 counterparts.
Because the M130 and M110 shared tooling, MercedesâÂÂBenz retired the M130 completely and transferred its production capacity to the M110. At the same time, the veteran M180 underwent a major redesign. The block retained the even cylinder spacing of the M130 and adopted the 86â¯mm bore to share pistons with the M110, optimising production. However, the stroke was shortened to 72.4â¯mm. The result was a very oversquare 86â¯ÃÂâ¯72.4â¯mm geometry, yielding a displacement.
The short stroke allowed MercedesâÂÂBenz to keep the fourâÂÂpin crankshaft with large bearing journals and no counterweights. This produced smooth midâ to highâÂÂrpm operation but at the cost of high fuel consumption. As intended, most buyers were commercial fleet operators, particularly for stretched sixâÂÂdoor taxicabs. Private sales were less successful, especially after the modular M102 engine arrived in the 230E and 230TE in 1980, offering similar performance at lower cost and better economy. Sales plummeted, leading to the early retirement of the estate version in 1982.
Originally the M123 V 23 (123.920) had an 8.7:1 compression ratio and produced 129â¯hp (95â¯kW) at 5500â¯rpm and 196â¯N÷m at 3500â¯rpm (piston speeds 13.2â¯m/s max, 8.4â¯m/s mean).
In September 1979 a power increase came with a 9.0:1 compression ratio, raising output to 140â¯hp (103â¯kW) at 5500â¯rpm and 200â¯N÷m at 3500â¯rpm (piston speeds 13.2â¯m/s max, 8.4â¯m/s mean).
In 1985 this engine was replaced by the modular M103 engine in the 2.6âÂÂlitre displacement.
The final iteration of the family was the M110, featuring a crossâÂÂflow DOHC 12âÂÂvalve cylinder head with hemispherical combustion chambers. A slightly reduced bore () was chosen to protect the cylinder walls from the expected higher compression and rpm. Although covered in a separate article, it used the M130âÂÂs cylinder block and can be considered part of this engine family. It served as the flagship for the midâÂÂrange W114 and W123 models and the entryâÂÂlevel engine for the W116 and W126 SâÂÂClasses, as well as the R107 SL and C107 SLC. Its replacement arrived in the form of the modular M103 in the larger 3.0âÂÂlitre displacement in 1985, but it continued to be used in the W460 280GE GâÂÂWagen until 1991.