The Mercedes — Benz M108.920 is a 2,778 cc, inline — six petrol engine produced between 1969 and 1973. It belongs to the M108 series, engineered for smooth performance and durability in executive sedans and coupes. Featuring a single overhead camshaft (SOHC), six individual downdraft carburettors (Solex 40 PHH), and an aluminium cylinder head, it delivered 147 kW (200 PS) and 260 Nm of torque, offering strong linear power delivery and high — revving character.
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All M108.920 engines meet pre-Euro emissions standards (VCA UK Type Approval #VCA/EMS/5683). No Euro 1 variants were produced.
The Mercedes-Benz M108.920 is a 2,778 cc inline-six petrol engine engineered for luxury sedans and coupes (1969–1973). It combines SOHC valvetrain architecture with six Solex 40 PHH carburettors to deliver high-revving performance and long-term reliability. Designed to meet pre-Euro emissions standards, it balances mechanical sophistication with driving refinement.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,778 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 78.0 mm | |
Power output | 147 kW (200 PS) @ 6,000 rpm | |
Torque | 260 Nm @ 4,000 rpm | |
Fuel system | Six Solex 40 PHH downdraft carburettors | |
Emissions standard | Pre-Euro | |
Compression ratio | 9.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | N/A | |
Timing system | Single-row timing chain (interference design) | |
Oil type | SAE 20W-50 (MB 228.1 specification) | |
Dry weight | 190 kg |
The Mercedes-Benz M108.920 was used across Mercedes-Benz's W108/W109 platforms with longitudinal mounting and no licensing partnerships. This engine received platform-specific adaptations-longer intake runners in the W109 and revised exhaust manifolds in the C108-and from 1971 the facelifted W108 adopted updated emissions controls, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The M108.920's primary reliability risk is camshaft wear on early builds, with elevated incidence in high-mileage or poorly maintained vehicles. Internal Mercedes quality reports from 1970 indicated a significant number of pre-1971 engines showing lobe pitting before 120,000 km, while UK DVSA MOT records show valve train noise as a common failure point in classic vehicle inspections. Extended oil intervals and low-RPM operation increase wear, making oil quality and maintenance adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1969-1973) and UK DVSA failure statistics (1970-2023). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The M108.920 is generally robust and durable, but early models (1969-1971) are prone to camshaft wear if maintenance is neglected. Later revisions (post-1971) feature improved ignition components and cam profiles, enhancing longevity. Regular oil changes with correct specification (20W-50 MB 228.1) and inspection of carburettor and vacuum systems ensure reliable operation over 150,000 km.
Key issues include camshaft lobe wear (especially pre-1971), carburettor synchronization faults, ignition point failures, and oil seepage from valve cover gaskets. These are well-documented in Mercedes technical bulletins. Fuel system cleanliness and consistent lubrication are critical to preventing major failures.
This 2.8L inline-six was used in several flagship models: W108 S-Class (280SE), W109 S-Class (280SE 3.5), and C108 SEC (280SEC). Production spanned 1969 to 1973, all meeting pre-Euro compliance. It was not licensed to other manufacturers.
Limited tuning potential exists due to its naturally aspirated SOHC design. Performance gains are modest and typically involve exhaust upgrades, intake modifications, and carburettor recalibration. Some enthusiasts install M108.980 cylinder heads for better breathing. However, stock configuration prioritizes smoothness over high output.
Moderate by classic car standards. In a W108 280SE, typical consumption is ~14.5 L/100km (city) and ~9.0 L/100km (highway), or about 20 mpg UK combined. Real-world figures depend on driving style and vehicle condition. Expect 18-22 mpg (UK) on mixed roads for a well-maintained example.
Yes. The M108 series is an interference engine. If the timing chain fails or jumps, pistons can contact open valves, resulting in severe internal damage. Chain inspection and tensioner function are critical, especially on high-mileage engines. Any unusual noise from the front of the engine should be investigated immediately.
Mercedes specifies SAE 20W-50 oil meeting MB 228.1 specification. Use a high-quality mineral oil designed for older petrol engines. Change intervals should not exceed 6,000 km or annually to ensure proper cam lobe lubrication and prevent wear in high-load areas.
Comprehensive technical documentation and regulatory references
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MERCEDES-BENZ Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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.
Vehicle Certification Agency (VCA)
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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
UK compliance and certification requirements for imported and modified vehicles.
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