Mercedes-Benz M 123
| Mercedes Benz | |
|---|---|
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| M 123 | |
| Manufacturer: | Mercedes Benz |
| Production period: | 1976-1985 |
| Design: | Inline six-cylinder |
| Engines: | 2.5 liters (2525 cm³) |
| Previous model: | M 180 |
| Successor: | M 103 |
The M 123 is a six-cylinder in - line engine from Daimler-Benz . The gasoline engine with chain-driven overhead camshaft (OHC) and counter-current cylinder head was used in the models 250 and 250 T of the 123 series from 1976 to 1985 . It replaced the M 180 of the 230.6 and M 130 of the 250 2.8 engines of the 114 series . The successor was the M 103 , which was introduced in the 124 series in 1984 .
The engine still has essential features of its predecessor. The crankshaft has only four bearings, and the oil pump, fuel pump and ignition distributor are driven by an inclined shaft at the front end of the engine, which in turn is driven by a chain wheel and a pair of helical gears. On the other hand, the cylinders are no longer cast together in pairs, but the cylinder spacing is uniform. There are no cast-in cooling channels in the partition walls between the cylinders, instead slots are cut through through which the cooling water flows.
The vertically hanging valves are operated by rocker arms and are arranged in two rows. As with the M 115 , the inlet and outlet are on the right side of the engine, and on the left side in the cylinder head there is a recessed combustion chamber (with a flat piston crown), in which the exhaust valve and the spark plug are located. The rest of the cylinder cross-section forms a squeeze surface that swirls the mixture in the combustion chamber.
While the rest of the engine range was taken over from the predecessor, the M 123 was the only new development that failed to convince customers. In 1979 the engine was revised, with the output increasing from 95 kW (129 PS) to 103 kW (140 PS). However, especially after the presentation of the new four-cylinder M 102 in the 200 and 230 E models, public interest declined sharply. The M 102 could do almost everything better, and fuel consumption was also considerably lower. The station wagon (250T) was canceled in 1982, the engine in the sedan (250) was available until 1985, but no longer played a major role in sales.
The Solex double register carburetor of type 4A1 with its four air funnels ( Venturi tube ) is considered to be relatively difficult to control today. It is identical to the carburetor of the Mercedes 280 of the predecessor series W 114. Three cylinders are supplied by a set of mixing systems (air funnels). A single set consists of a relatively small air funnel for idling and medium speeds and a larger sized second funnel for full load operation. When idling and up to a third of load, only the two smaller systems are mechanically activated by the accelerator pedal; the two full-load systems are also opened by a vacuum unit at high load and speed. A central float chamber supplies all four mixing systems with fuel. In this double-register carburetor, as is customary with injection engines, the fuel supply is designed with flow and return lines; this ensures a cooling effect for the gasoline flowing back to the tank and thus a certain degree of security against the formation of vapor bubbles and the resulting starting problems when the engine is hot and / or in summer temperatures.
Shortly before the introduction of the first carburettor that worked with a catalytic converter and was electrically controlled according to lambda probe data (approx. 1986/87), this type of four-pipe carburetor was roughly the most complex that came out of Wilhelm Maybach's invention of the spray nozzle carburetor after 80 years of development had become. When the lambda probes came, which are necessary for the three-way catalytic converter to regulate the richness of the mixture, this complex type of carburettor was already a thing of the past and had been replaced by manifold injection , which is simpler and easier to maintain.
The joy of smooth running was marred by high fuel consumption, but this engine was again noticeably more economical than the 280 carburettor models (which often consumed more than 17 liters in city traffic) and thus achieved its most important development goal. However, this was done better in every respect by the successor type M 103 from 1984, which was cheaper to produce in the variant with 2.6 liters displacement, was lighter and considerably more economical, with increased engine output of initially 122 kW (166 hp) or with Kat 118 kW (160 PS) and better revving power compared to the comparatively sluggish M 123. The smoothness of the M 103 was again considerably better, especially in the 2.6 l variant.
Use:
Data:
- Bore 86 mm, stroke 72.45 mm, displacement 2525 cm 3
- Compression 8.7: 1
- Output 95 kW (129 hp) at 5500 rpm
- Torque 196 Nm at 3500 rpm
- Top speed: 175 km / h
In 1979 the engine was revised:
- Compression 9.0: 1
- Output 103 kW (140 PS) at 5500 rpm
- Torque 200 Nm at 3500 rpm
In October 1981 the M 123 was revised again to reduce fuel consumption. The compression was increased to 9.4: 1 by changing the combustion chambers in the cylinder head; the other data remained the same. At the same time, the internal type designation of the engine was changed from M 123.920 to M 123.921.
