The Mercedes — Benz M117.982 is a 5,547 cc, V8, naturally aspirated petrol engine produced between 1977 and 1991. It belongs to the M117 engine family, featuring a single overhead camshaft (SOHC) per bank, hemispherical combustion chambers, and Bosch K — Jetronic mechanical fuel injection. Delivering 180 kW (245 PS) at 5,000 rpm and 400 Nm of torque at 3,000 rpm, it provided smooth, effortless power delivery for flagship luxury applications.
Fitted primarily to the W126 S…
Production years 1977–1986 meet pre-Euro standards; 1987–1991 models comply with Euro 1 (ECE R83-03). Vehicle Certification Agency (VCA) Type Approval records confirm conformity for UK-market variants.
The Mercedes-Benz M117.982 is a 5,547 cc V8 petrol engine developed for luxury flagship applications (1977–1991). It features SOHC valvetrain architecture with mechanical fuel injection, delivering smooth power delivery and mechanical refinement. Designed to meet evolving emissions regulations, it balances period-correct performance with long-term durability.
| Parameter | Value | Source |
|---|---|---|
Displacement | 5,547 cc | |
Fuel type | Petrol | |
Configuration | V8, SOHC, 16-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 100.0 mm × 88.5 mm | |
Power output | 180 kW (245 PS) @ 5,000 rpm | |
Torque | 400 Nm @ 3,000 rpm | |
Fuel system | Bosch K-Jetronic mechanical fuel injection | |
Emissions standard | Pre-regulatory (1977–1986); Euro 1 (1987–1991) | |
Compression ratio | 8.8:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Chain-driven (duplex), front-mounted | |
Oil type | SAE 20W-50 mineral (API SF/CC) | |
Dry weight | 238 kg |
The Mercedes-Benz M117.982 was used across Mercedes-Benz's W126/R107 platforms with longitudinal mounting and no licensing partnerships. This engine received platform-specific adaptations-tuned intake manifolds for saloon versus coupe applications-and from 1984 the updated W126.028 series adopted revised valve train components, creating interchange limits. All adaptations are documented in OEM technical bulletins.
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The M117.982's primary reliability risk is timing chain tensioner wear on early builds, with elevated incidence in high-mileage or poorly maintained examples. Internal Mercedes-Benz service reports from 1985 noted increased chain noise in pre-1984 units exceeding 100,000 km, while VCA inspection records show a notable share of emissions-related failures linked to fuel head imbalance in vintage vehicles. Extended oil change intervals and use of incorrect viscosity oils accelerate wear, making adherence to factory service intervals critical.
Analysis derived from Mercedes-Benz technical bulletins (1977-1991) and UK DVSA vintage vehicle inspection statistics (2018-2023). Repair procedures should follow manufacturer guidelines.
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The M117.982 is mechanically robust when properly maintained. Early models (1977-1983) had timing chain tensioner issues, but post-1984 revisions improved durability. Regular oil changes with SAE 20W-50, K-Jetronic servicing, and cooling system maintenance are essential. Well-kept examples can exceed 200,000 km with minimal issues.
Key issues include timing chain tensioner wear (especially pre-1984), K-Jetronic fuel head imbalance, cooling system leaks, and hydraulic tappet noise. These are documented in Mercedes-Benz service literature and addressed through OEM-recommended updates and maintenance procedures.
The M117.982 was used in the W126 500SEL/560SEL (1977–1991) and the R107 500SL/560SL (1977–1989). It was not used in coupes or convertibles outside of the R107 platform. No cross-manufacturer applications exist for this variant.
Limited tuning potential exists. Performance upgrades include high-flow air filters, tuned exhaust manifolds, and modified camshafts. ECU tuning is not applicable—fuel delivery is mechanical. Realistic gains are +20–30 PS with supporting modifications. Forced induction conversions are possible but require extensive engineering.
Factory figures indicate ~18.0 L/100km (15.7 mpg UK) in combined driving. Real-world consumption ranges from 16.0–22.0 L/100km (12–18 mpg UK) depending on driving style and vehicle condition. Fuel head calibration and tyre pressure significantly affect efficiency.
No. The M117.982 is a non-interference engine. If the timing chain fails, piston-to-valve contact is unlikely, reducing risk of catastrophic internal damage. However, immediate repair is still advised to prevent secondary damage from incorrect valve timing.
Mercedes-Benz specifies SAE 20W-50 mineral oil meeting API SF/CC standards. Modern synthetic blends with equivalent viscosity are acceptable if compatible with vintage engine materials. Change intervals should not exceed 15,000 km or annually to ensure optimal lubrication of the timing chain and hydraulic tappets.
Comprehensive technical documentation and regulatory references
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Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
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)
UK type-approval authority for automotive products.
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.
VCA Certification Portal
Type-approval guidance and documentation.
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