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The Mercedes Benz M186 Engine was a 3.0–litre single overhead camshaft inline-6 developed in the early 1950s to power the company's new flagship 300 "Adenauer" (W186) four-door saloon. It made its debut at the Frankfurt Motor Show in April 1951.

Mercedes-Benz M186 engine
M198 variant
Overview
Production	1951–1967
Layout
Configuration	inline-6
Displacement	3.0 L; 182.8 cu in (2,996 cc)
Cylinder bore	85 mm (3.35 in)
Piston stroke	88 mm (3.46 in)
Head material	Aluminum
Valvetrain	SOHC 2 valves x cyl.
RPM range
Redline	6000[1]
Combustion
Fuel system	3 downdraft Solex carburettors Bosch Fuel injection
Fuel type	Gasoline
Cooling system	Water-cooled
Output
Power output	115–240 bhp (86–179 kW)
Torque output	294 N⋅m (217 lb⋅ft) (M198 300 SL)

Designed to give reliable service under prolonged hard use, the iron block/aluminum head engine featured deep water jackets, an innovative diagonal head-to-block joint that allowed for oversized intake and exhaust valves, reverse-flow cylinder head, thermostatically controlled oil cooling, copper-lead bearings, and a hardened crankshaft.

Variants of the M186 went on to be used in the exclusive 300 S/300 Sc gran tourer, iconic gullwing 300SL sports car, and Mercedes top-end 300-series sedans and limousines, and coupes of the early to mid-1960s. Production ended in 1967, four years after the introduction of the 600 Grosser Mercedes and the 6.3 L (386.4 cu in) M100 V-8.

The various versions of the engine (M186 – M199) produced from 115–240 bhp (86–179 kW) as compression ratios rose and the number of carburettors multiplied or were replaced with fuel-injection.[2]

While sharing many design features with Mercedes' 2.2 L (134 cu in) M180 engine introduced at the same show (such as staggered valve arrangement and rockers running off a single overhead camshaft driven by a duplex cam-chain), the two were of completely different design with little or no inter-changeability of parts.[3]

The term "big six" is sometimes used to distinguish the large block 3.0 L M186 from the small block M180 and its derivatives.

M186 Variants

M186

The 3.0–litre (2,996 cc (3.0 L; 182.8 cu in)) M186 was introduced in 1951 for use in the company's flagship 300 "Adenauer" (W186) four-door saloon. It had a slightly under-square bore and stroke of 85 mm × 88 mm (3.35 in × 3.46 in), featured an overhead cam, and an aluminum head with an innovative 30-degree diagonal head-to-block joint that allowed for oversized intake and exhaust valves. Designed to give reliable service under prolonged hard use, the engine featured deep water jackets, thermostatically controlled oil cooling, copper-lead bearings, and a hardened crankshaft. Fitted with twin downdraft Solex carburettors it produced 115 bhp (117 PS; 86 kW)[4] at a 6.4:1 compression ratio.

M188

The W188 300 S coupé/cabriolet was released in 1952 with the M188 variant, being fed by triple downdraft Solex carburettors and producing 150 hp (112 kW) at 5000 rpm and 7.8:1 compression ratio.

M189

The first M189 appeared in the 300d pillarless limousine of 1957, three years after the M198. It used Bosch indirect fuel injection to up performance from the underpowered M186 to 180 PS (132 kW; 178 hp) at 5500 rpm.[5] The engine then appeared in 1961 in the Mercedes-Benz W112 300SE and its long wheelbase derivative (also called 300SE; the SEL nomenclature would first be used on the subsequent W109 LWB sedans) two years later. From 1964, power output was 170 hp (127 kW). The final incarnation of the M189 was in the W108 300SEb and W109 300SEL of 1965–1967, producing 170 hp (127 kW).

M198

The high-performance M198 was created in 1954 for the first generation of the 300SL, known colloquially as the "Gullwing". To fit under its low profile hood the engine was tilted 50-degrees to the left.[6][7] The result for the car was aerodynamic efficiency, and an enormous sand-cast aluminum intake manifold that stretched across the engine's entire breadth.[8] In order to deliver track-ready performance, race-derived features were built in, including a dry sump lubrication system and Bosch mechanical direct fuel-injection, one of the first production cars with fuel injection. This engine produced 215 PS (158 kW; 212 hp) DIN net at 5,800 rpm and 275 N⋅m (203 lb⋅ft) DIN net of torque at 4,600 rpm[1] and 243 PS (179 kW; 240 hp) net (brake hp) at 6,100 RPM and 294 N⋅m (217 lb⋅ft) net torque at 4,800 RPM. An optional high-performance "Sport" camshaft was also available. This was the only available configuration for the Roadster version of the 300 SL when it made its debut in 1957.[1] Production ended in 1964.

M199

A significantly detuned direct-injection, dry sump oil system engine was used in the late W188 300 Sc of 1955 to 1958 producing 175 hp (130 kW) at 5400 rpm and 8.55:1 compression ratio

See also

• Mercedes-Benz M180 engine
• List of Mercedes-Benz engines

References

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