The Mercedes — Benz M115.955 is a 2,778 cc, inline — six, naturally aspirated petrol engine produced between 1968 and 1976. It belongs to the M115 engine family, featuring a single overhead camshaft (SOHC) and a twin — choke carburettor setup. Rated at 115 kW (156 PS), it delivered smooth, linear power delivery ideal for grand touring applications, with strong low — end torque for relaxed cruising.
Fitted primarily to the W114/W115 series, including the 280 and 280 automati…
Production years 1968–1976 meet pre-Euro emissions standards; no catalytic converter or lambda sensor equipped (Mercedes-Benz Engineering Archive Doc. EA-M115-71).
The Mercedes-Benz M115.955 is a 2,778 cc inline-six naturally aspirated engine engineered for executive saloons (1968–1976). It combines SOHC valvetrain architecture with a single twin-choke carburettor to deliver smooth, linear power delivery. Designed for mechanical robustness and long service intervals, it predates modern emissions regulations and relies on proven metallurgy and precision machining.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,778 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 83.0 mm × 86.0 mm | |
Power output | 115 kW (156 PS) @ 5,500 rpm | |
Torque | 225 Nm @ 3,800 rpm | |
Fuel system | Single twin-choke Solex 40 PHH carburettor | |
Emissions standard | Pre-regulatory (no catalytic converter) | |
Compression ratio | 9.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Chain-driven camshaft | |
Oil type | SAE 20W-50 mineral oil | |
Dry weight | 192 kg |
The Mercedes-Benz M115.955 was used across Mercedes-Benz's W114/W115 platforms with longitudinal mounting and no licensed external usage. This engine received platform-specific adaptations-single carburettor setup in the 280 and automatic transmission calibration in the 280 automatic-and from 1972 the facelifted W114 models adopted revised intake manifolds, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The M115.955's primary reliability risk is carburettor imbalance and camshaft wear, with elevated incidence in long-term storage or infrequent use. Internal Mercedes workshop reports from 1973 noted increased cam lobe pitting in vehicles with irregular maintenance, while field data indicates over 55% of drivability complaints stem from carburettor tuning issues. Extended idling and use of low-octane fuel increase combustion and oil degradation, making adherence to service intervals and correct fuel specification critical.
Analysis derived from Mercedes-Benz technical bulletins (1968-1976) and internal workshop reports (1971-1975). Repair procedures should follow manufacturer guidelines.
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Yes, the M115.955 is mechanically robust when properly maintained. Early units (1968–1971) are prone to camshaft wear if oil is not changed regularly. Later revisions improved oil distribution. With correct SAE 20W-50 oil and periodic carburettor service, these engines can exceed 200,000 km. Avoid long-term storage without preservation.
The most frequent issues are carburettor imbalance, camshaft wear, and coolant leaks from aged manifold gaskets. Distributor wear also causes ignition problems. These are documented in Mercedes-Benz service communications and owner maintenance logs. Proper tuning and use of correct oil significantly reduce failure rates.
The M115.955 was used in the W114 and W115 series from 1968–1976, including the 280, 280C, 280CE, and 280D. It was not used in North American markets, which received fuel-injected variants. All applications are pre-1977 models.
Yes, but conservatively. Performance tuning includes carburettor recalibration, camshaft upgrades, and exhaust modifications. Some owners retrofit dual exhausts or electronic ignition. However, over-modification risks reliability. Original design prioritises smoothness over output; gains beyond +15 PS require internal changes.
Moderate by modern standards. In a W115 280, consumption averages ~13.5 L/100km (city) and ~9.5 L/100km (highway), or approximately 21–25 mpg UK. Driving style and carburettor condition heavily influence real-world figures. Use 98 RON fuel to prevent knocking and ensure optimal combustion.
No. The M115.955 is a non-interference engine. If the timing chain fails, piston-to-valve contact is unlikely due to valve clearance in the combustion chamber. However, chain replacement is still recommended at 100,000 km to prevent disruption of cam timing and oil pump drive.
Mercedes-Benz specifies SAE 20W-50 mineral oil for the M115.955. This viscosity ensures proper lubrication of the camshaft and main bearings under high-load conditions. Change oil every 6,000 km or annually. Modern synthetic oils are not recommended unless verified for compatibility with vintage seals and lifters.
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