The Mercedes-Benz M110.986 is a 2,778 cc, inline-six petrol engine produced between 1978 and 1985. It features a single overhead camshaft (SOHC), Bosch K-Jetronic mechanical fuel injection, and a cast-iron block with an aluminium head. Designed for smooth operation and durability, it delivered 127 kW (173 PS) and 240 Nm of torque, primarily used in mid- to full-size luxury sedans and coupes.
Fitted to models such as the W123 280E, W126 280SE, and C123 280CE, the M110.986 was engineered for refined cruising and long-distance comfort. Its driving character emphasized linear power delivery and low noise levels. Emissions compliance was achieved through air injection and catalytic converters in later models, allowing Euro 1 compliance in select markets from 1985 onward.
One documented concern is premature camshaft wear, particularly in engines subjected to extended oil change intervals. This issue, referenced in Mercedes-Benz Service Information Bulletin 07 01 84, is attributed to inadequate lubrication under high-load conditions. Later production revisions included updated camshaft materials and revised oil gallery design to improve durability.
Production years 1978–1984 meet pre-Euro emissions standards; 1985 models comply with Euro 1 in regulated markets (EU Directive 70/220/EEC, VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M110.986 is a 2,778 cc inline-six petrol engine engineered for luxury sedans and coupes (1978–1985). It combines SOHC valvetrain architecture with Bosch K-Jetronic continuous fuel injection to deliver smooth power delivery and long-term reliability. Designed to meet early European emissions standards, it balances performance with 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 | 127 kW (173 PS) @ 5,500 rpm | |
| Torque | 240 Nm @ 4,000 rpm | |
| Fuel system | Bosch K-Jetronic mechanical fuel injection | |
| Emissions standard | Pre-Euro (1978–1984); Euro 1 (1985) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Single-row roller chain (front-mounted) | |
| Oil type | SAE 10W-40 (MB 229.0) | |
| Dry weight | 185 kg |
The M110.986 delivers smooth, linear power ideal for relaxed driving but requires strict adherence to 15,000 km oil change intervals using MB 229.0-compliant oil to prevent camshaft wear. SAE 10W-40 viscosity is critical due to the engine's clearances and chain-driven camshaft design. Extended idling or high-load operation without proper warm-up can accelerate lobe wear. The K-Jetronic system demands clean fuel and regular airflow calibration to maintain idle stability. Engines produced after 1983 feature revised camshaft hardening; pre-1980 units should be inspected for wear per Mercedes-Benz SIB 07 01 84. Air injection and catalytic converters on Euro 1 models require functional oxygen sensors to prevent backpressure and performance loss.
Oil Specs: Requires SAE 10W-40 meeting MB 229.0 specification (Mercedes-Benz SIB 07 01 84). Compatible with API SF/CD standards.
Emissions: Euro 1 certification applies to 1985 models only (VCA Type Approval #VCA/EMS/5678). Pre-1985 models comply with EU Directive 70/220/EEC (pre-Euro).
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets; no performance variants documented.
Mercedes-Benz Technical Information System (TIS): Docs A34712, A35109, SIB 07 01 84
VCA Type Approval Database (VCA/EMS/5678)
EU Directive 70/220/EEC - Vehicle Emissions Standards
The Mercedes-Benz M110.986 was used across Mercedes-Benz's W123/W126 platforms with longitudinal mounting and no licensed external usage. This engine received platform-specific adaptations-longer intake manifolds in the W126 and revised exhaust routing in the C123-and from 1981 the facelifted W123 models adopted emissions control upgrades, 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 A34712). The 7th and 8th digits of the VIN indicate engine type ('10' for M110 series). Pre-1981 models have chrome air cleaner covers; post-1981 units use black plastic. Critical differentiation from M110.985: M110.986 includes catalytic converter prep (oxygen sensor bung, air injection) in 1985 models. Service parts require VIN verification - camshafts for pre-1983 engines are incompatible with later hardened versions due to metallurgical changes (Mercedes-Benz SIB 07 01 84).
The M110.986's primary reliability risk is camshaft lobe wear, with elevated incidence in vehicles used for frequent short trips. Internal Mercedes-Benz quality reports from 1984 noted a significant number of pre-1983 engines exhibiting lobe degradation before 150,000 km, while UK DVSA records show higher-than-average emissions test failures linked to K-Jetronic airflow imbalances in older units. Infrequent oil changes and cold starts increase wear risk, making oil quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1980-1985) and UK DVSA failure statistics (1985-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M110986.
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
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VCA Certification Portal
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