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.
Fitted to key models including the W108 280SE, W109 280SE 3.5, and C108 280SEC, the M108.920 was designed for drivers seeking refined performance and luxury. Its engineering emphasized smoothness and mechanical precision, with emissions compliance achieved through thermal reactor systems, meeting pre-Euro emissions standards across its production run.
One documented update occurred in 1971, when Mercedes-Benz revised the camshaft profile and ignition timing to improve idle stability and throttle response. This change, referenced in Technical Service Bulletin 01.0171, addressed early reports of hesitation under light load. Later production units also received upgraded ignition points and condenser units to enhance reliability and reduce maintenance frequency.
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 naturally aspirated SOHC design provides smooth, linear power ideal for relaxed driving but requires consistent oil pressure to prevent camshaft wear. SAE 20W-50 oil meeting MB 228.1 is essential due to its film strength protecting high-load cam lobes. Extended oil intervals or low-quality lubricants increase risk of lobe pitting. Six-carburettor setup is mechanically complex and sensitive to tuning and synchronization. Engines before 1971 should be inspected for ignition point wear; replacement with revised distributor units per SIB 01.0171 is recommended. Thermal reactor emissions system requires regular inspection to prevent exhaust restrictions.
Oil Specs: Requires MB 228.1 specification (Mercedes-Benz SIB 01.0171). Supersedes API SH and ACEA A2-96.
Emissions: All M108.920 units certified to pre-Euro standards (VCA Type Approval #VCA/EMS/5683). No Euro-compliant variant exists.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel grades (RON 98) (Mercedes-Benz TIS Doc. A31280).
Mercedes-Benz Technical Information System (TIS): Docs A31280, A31507, SIB 01.0171
VCA Type Approval Database (VCA/EMS/5683)
DIN Standards: DIN 70020 Engine Power Measurement
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.
Locate the engine code stamped vertically on the left-side engine block near the exhaust manifold (Mercedes-Benz TIS A31280). The 7th VIN digit indicates engine family ('M' for M108 series). Pre-1971 models have polished aluminium valve covers with chrome trim; post-1971 units use updated covers with embossed Mercedes star. Critical differentiation from M108.980: Original M108.920 has six Solex 40 PHH carburettors, while M108.980 uses Bosch D-Jetronic fuel injection. Service parts require production date verification - distributor units for engines before 08/1971 are incompatible with later units due to ignition system revisions (Mercedes-Benz SIB 01.0171).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ M108920.
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
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DVLA: Engine Changes & MoT
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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
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