The Mercedes-Benz M103.942 is a 2,962 cc, inline-six petrol engine produced between 1984 and 1997. It formed part of the M103 series, known for smoothness and durability in Mercedes' mid-to-large sedan and coupe lineup. Featuring a single overhead camshaft (SOHC), multi-point fuel injection (Bosch KE-Jetronic or LE-Jetronic), and aluminium cylinder head, it delivered 136 kW (185 PS) and 260 Nm of torque, offering strong linear power delivery for relaxed cruising.
Fitted to key models including the W124 260E, W126 260SE, and R107 280SL - commonly found in the 260E, 260SE, and 280SL variants - the M103.942 was engineered for smooth, refined performance and long-distance comfort. Its design emphasized reliability and serviceability, with emissions compliance achieved through catalytic converters and lambda control systems, meeting Euro 1 standards in later production years.
One documented concern is premature camshaft wear, particularly in early-series engines built before 1988. This issue, referenced in Mercedes-Benz Technical Service Bulletin 01.0188, is attributed to insufficient lubrication at the cam lobes under high-load conditions. Later revisions introduced modified camshaft materials and updated oil gallery design to improve durability.
Production years 1984–1992 meet Euro 1 standards; certain 1993–1997 models may have Euro 2 compliance depending on market (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M103.942 is a 2,962 cc inline-six petrol engine engineered for executive sedans and grand tourers (1984–1997). It combines SOHC valvetrain architecture with Bosch KE-Jetronic continuous fuel injection to deliver smooth power delivery and long-term reliability. Designed to meet Euro 1 (and select Euro 2) emissions standards, it balances refinement with durability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,962 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 83.6 mm | |
| Power output | 136 kW (185 PS) @ 5,500 rpm | |
| Torque | 260 Nm @ 4,000 rpm | |
| Fuel system | Bosch KE-Jetronic (mechanical-electronic continuous injection) | |
| Emissions standard | Euro 1 (pre-1993); Euro 2 depending on market | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | N/A | |
| Timing system | Single-row timing chain (interference design) | |
| Oil type | SAE 10W-40 (MB 229.0 specification) | |
| Dry weight | 185 kg |
The naturally aspirated SOHC design provides smooth, linear power ideal for relaxed driving but requires consistent oil pressure to prevent camshaft wear. SAE 10W-40 oil meeting MB 229.0 is essential due to its film strength protecting high-load cam lobes. Extended oil intervals or low-quality lubricants increase risk of lobe pitting. KE-Jetronic injection is robust but sensitive to vacuum leaks and warm-up regulator faults. Engines before 1988 should be inspected for cam wear; replacement with revised hard-faced camshafts per SIB 01.0188 is recommended. Catalytic converters on post-1988 models require lead-free fuel to prevent poisoning.
Oil Specs: Requires MB 229.0 specification (Mercedes-Benz SIB 01.0188). Supersedes API SH/SL and ACEA A2-96.
Emissions: Euro 1 certification applies to pre-1993 models only (VCA Type Approval #VCA/EMS/5678). Some 1993-1997 models meet Euro 2 depending on market.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel grades (RON 95) (Mercedes-Benz TIS Doc. A31275).
Mercedes-Benz Technical Information System (TIS): Docs A31275, A31502, SIB 01.0188
VCA Type Approval Database (VCA/EMS/5678)
DIN Standards: DIN 70020 Engine Power Measurement
The Mercedes-Benz M103.942 was used across Mercedes-Benz's W124/W126/R107 platforms with longitudinal mounting and no licensing partnerships. This engine received platform-specific adaptations-longer intake manifolds in the W126 and revised exhaust routing in the R107-and from 1993 the facelifted W124 adopted updated emissions controls, 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 A31275). The 7th VIN digit indicates engine family ('M' for M103 series). Pre-1988 models have polished aluminium valve covers with black decals; post-1988 units use ribbed covers with embossed logo. Critical differentiation from M103.970: Original M103.942 has Bosch KE-Jetronic CIS with round fuel distributor, while M103.970 uses LE-Jetronic with electronic injectors. Service parts require production date verification - camshafts for engines before 08/1988 are incompatible with later units due to material and oil feed revisions (Mercedes-Benz SIB 01.0188).
The M103.942'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 1989 indicated a significant number of pre-1988 engines showing lobe pitting before 150,000 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 (1988-1995) and UK DVSA failure statistics (1990-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M103942.
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