Mercedes-Benz M186 engine

The Mercedes Benz M186 Engine was a 3.0 litre single overhead camshaft inline-6 developed 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.

Variants of the M186 went on to be used in the exclusive 300 S/300 Sc, iconic gullwing 300SL, and 300SE sedans of the early 1960s.

While sharing many design features with Mercedes' 2.2 litre (134ci) 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.

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

The 3.0 litre ‘big six’ was produced from 1951 until 1967 with no change in its 2996 cc/182 in³ displacement derived from a slightly under-square 85 mm x 88 mm bore and stroke. It featured an overhead cam, and an aluminum head with an innovative diagonal head-to-block joint that allowed for oversized intake and exhaust valve. The various versions of the engine (M186 – M199) produced from 115 bhp (86 kW) – 215 bhp (160 kW) as compression ratios rose and the number of carburettors multiplied or were replaced with fuel-injection.

The first variant of the engine was released in the W186 300 Adenauer sedan in 1951. This twin downdraft Solex carburettor version produced 115 hp (86 kW) at a 6.4:1 compression ratio and ran until the introduction of the 300b in 1954. Different Solex carburettors and an increased compression ratio of 7.5:1 saw power increase to 125 hp (93 kW) on the 300c through 1957.

The W188 300 S coupe/cabriolet was released in 1952 with the M188 variant, being fed by triple downdraft Solex carburettors and producing 150 hp (110 kW).

The first M189 appeared in the 300d pillarless limousine of 1957, sporting Bosch indirect fuel injection and producing 180 PS (130 kW; 180 hp) at 5500 rpm. The engine then appeared in the Mercedes-Benz W112 300SE of 1961 and its long wheelbase SEL variant two years later. From 1964, power output was 170 hp (130 kW). The final incarnation of the M189 was in the W108 300SEb and W109 300SEL of 1965-1967, producing 170 hp (130 kW).

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Wikipedia