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 W11…
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 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.
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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.
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Yes, the M114.920 is mechanically robust when properly maintained. Early units (1965–1970) 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 M114.920 was used in the W108 and W114/W115 series from 1965–1972, including the 250S, 250SE, 250, 250C, and 250CE. It was not used in North American markets, which received the fuel-injected M129 variant. All applications are pre-1973 models.
Aftermarket ECU tuning is common on the M114920 platform, but increasing boost or altering engine parameters accelerates component wear, impacts emissions compliance, and may void vehicle warranties. Any modifications should be evaluated carefully by a qualified specialist.
Moderate by modern standards. In a W108 250S, consumption averages ~12.5 L/100km (city) and ~9.0 L/100km (highway), or approximately 22–25 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 M114.920 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 M114.920. 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.
Comprehensive technical documentation and regulatory references
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GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
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