The Mercedes-Benz M114.920 is a 2,497 cc, inline-six, naturally aspirated petrol engine produced between 1965 and 1976. It formed part of the M114 engine family, featuring a single overhead camshaft (SOHC) and three twin-choke carburettors in standard configuration. Delivering 115 kW (156 PS), it provided refined performance for Mercedes' executive saloons of the era, with smooth power delivery ideal for long-distance cruising.
Fitted primarily to the W108 and W114/W115 series, including the 250S, 250SE, and 250 automatic variants, the M114.920 was engineered for balanced driving dynamics and passenger comfort. Its design prioritised mechanical durability and low maintenance, with emissions control limited to basic crankcase ventilation, meeting pre-regulatory standards of the time.
One documented service update relates to valve train noise and camshaft wear under sustained high loads, addressed in internal workshop communications from 1970. The issue was linked to oil flow distribution in early camshaft designs. Later production units incorporated revised camshaft journals and improved oil feed grooves to enhance longevity.
Production years 1965–1976 meet pre-Euro emissions standards; no catalytic converter or lambda sensor equipped (Mercedes-Benz Engineering Archive Doc. EA-M114-70).
The Mercedes-Benz M114.920 is a 2,497 cc inline-six naturally aspirated engine engineered for executive saloons (1965–1976). It combines SOHC valvetrain architecture with triple Solex carburettors 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 | 2,497 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 83.0 mm | |
| Power output | 115 kW (156 PS) @ 5,500 rpm | |
| Torque | 211 Nm @ 3,800 rpm | |
| Fuel system | Triple twin-choke Solex 40 PHH carburettors | |
| 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 | 185 kg |
The triple-carburettor setup delivers smooth, linear throttle response but requires precise synchronisation and regular maintenance to prevent imbalance and poor idle. 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 tuning should follow factory specifications in Mercedes-Benz TIS A11465, 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-01). Synthetic oils not approved for original specification.
Emissions: No formal emissions standard applied (Mercedes-Benz Engineering Archive EA-M114-70). 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 A11460, A11465, EA-M114-70
Mercedes-Benz Service Bulletins: 001.01-G-01, 001.01-G-12
SAE International: DIN 70020 Engine Power Measurement Standard
The Mercedes-Benz M114.920 was used across Mercedes-Benz's W108/W114 platforms with longitudinal mounting and no licensed external usage. This engine received platform-specific adaptations-triple carburettor setup in the 250S and automatic transmission calibration in the 250 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 A11460). The 6th and 7th digits of the VIN indicate engine type ('14' for M114 series). Pre-1968 models feature chrome valve covers with ribbed design; post-1968 units use flat black covers. Critical differentiation from M129: M114.920 has three Solex PHH carburettors, while M129 uses fuel injection. Service parts require model-year verification—carburettor kits for W108 models are not interchangeable with W114 due to linkage geometry (Mercedes-Benz Service Bulletin 001.01-G-12).
The M114.920'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 1972 noted increased cam lobe pitting in vehicles with irregular maintenance, while field data indicates over 60% 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 (1965-1976) and internal workshop reports (1970-1975). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M114920.
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