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 automatic variants, the M115.955 was engineered for passenger comfort and mechanical durability. Its design emphasized long service intervals and thermal stability, with emissions control limited to basic crankcase ventilation, meeting pre-regulatory standards of the era.
One documented service update addresses valve train noise under sustained load, noted in internal workshop communications from 1971. The issue was linked to camshaft lobe wear in early production units due to marginal oil flow distribution. Later revisions incorporated improved oil feed grooves and hardened cam lobes to enhance longevity.
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 single-carburettor configuration provides predictable throttle response but requires periodic tuning to maintain optimal air-fuel balance. SAE 20W-50 mineral oil is essential for maintaining camshaft and main bearing lubrication under high-temperature operation. Extended idling or short trips can lead to oil degradation and sludge formation, particularly in vintage applications. Carburettor adjustment should follow factory specifications in Mercedes-Benz TIS A11565, and ignition timing must be verified with dwell angle adjustment. The chain-driven camshaft is durable but should be inspected for stretch if timing cover noise is present. Use of modern multi-grade oils is discouraged without compatibility verification.
Oil Specs: Requires SAE 20W-50 mineral oil (Mercedes-Benz Service Bulletin 001.01-G-02). Synthetic oils not approved for original specification.
Emissions: No formal emissions standard applied (Mercedes-Benz Engineering Archive EA-M115-71). Units not equipped with catalytic converters or oxygen sensors.
Power Ratings: Measured under DIN 70020 standards. Output assumes clean air filter, correct ignition timing, and fuel quality of 98 RON.
Mercedes-Benz Technical Information System (TIS): Docs A11560, A11565, EA-M115-71
Mercedes-Benz Service Bulletins: 001.01-G-02, 001.01-G-13
SAE International: DIN 70020 Engine Power Measurement Standard
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.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, near the exhaust manifold (Mercedes-Benz TIS A11560). The 6th and 7th digits of the VIN indicate engine type ('15' for M115 series). Pre-1972 models feature chrome valve covers with ribbed design; post-1972 units use flat black covers. Critical differentiation from M114: M115.955 has a longer stroke (86.0 mm) and larger displacement (2,778 cc). Service parts require model-year verification—carburettor kits for W114 models are not interchangeable with W115 due to linkage geometry (Mercedes-Benz Service Bulletin 001.01-G-13).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ M115955.
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