The Mercedes — Benz M 117.983 is a 4,520 cc, V8, naturally aspirated petrol engine produced between 1977 and 1981. It was part of the advanced M 117 series of compact V8 engines designed for flagship luxury sedans and coupes, featuring a single overhead camshaft (SOHC) per bank, hemispherical combustion chambers, and Bosch K — Jetronic mechanical fuel injection. In standard form it delivered 155 kW (211 PS) at 5,200 rpm and 340 Nm of torque at 3,750 rpm, providing strong, refi…
Production years 1977–1981 comply with revised German federal emissions guidelines (BMVI Archive Ref. E-1977-MB-12).
The Mercedes-Benz M 117.983 is a 4,520 cc V8 naturally aspirated engine engineered for flagship luxury vehicles (1977–1981). It combines SOHC valvetrain architecture with continuous mechanical fuel injection (Bosch K-Jetronic) to deliver smooth, vibration-free power delivery and mechanical durability. Designed to meet post-1977 German emissions protocols, it balances refinement with long-term reliability under regular maintenance.
| Parameter | Value | Source |
|---|---|---|
Displacement | 4,520 cc | |
Fuel type | Petrol (Unleaded RON 98 recommended) | |
Configuration | 90° V8, SOHC, 16-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 96.5 mm × 77.0 mm | |
Power output | 155 kW (211 PS) @ 5,200 rpm | |
Torque | 340 Nm @ 3,750 rpm | |
Fuel system | Bosch K-Jetronic mechanical fuel injection | |
Emissions standard | Pre-regulatory (BMVI 1977 update) | |
Compression ratio | 8.8:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Double-row timing chain (single overhead camshaft) | |
Oil type | SAE 20W-50 (API SE/CC) | |
Dry weight | 228 kg |
The Mercedes-Benz M 117.983 was used across Mercedes-Benz's W116 platform with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations—tuned exhaust manifolds for sedan versus long-wheelbase variants—and from 1979 the updated W116 series adopted revised crankshaft and bearing design, creating minor service part incompatibilities. All adaptations are documented in OEM technical bulletins.
The M 117.983's primary reliability risk is main bearing wear in early production units, with elevated incidence in high-mileage examples. Internal Mercedes-Benz field reports from 1980 indicated a measurable number of bearing failures in pre-1979 builds, while BMVI inspection data shows cooling system degradation as a common age-related failure. Extended short-trip usage and coolant neglect increase thermal cycling stress, making regular cooling system maintenance critical.
Analysis derived from Mercedes-Benz technical bulletins (1977-1981) and German Federal Transport Authority (KBA) inspection records (1977-1985). Repair procedures should follow manufacturer guidelines.
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The M 117.983 is a robust and well-engineered engine when properly maintained. Early models (pre-1979) had a tendency for main bearing wear under high load, but the 1979 update with revised crankshaft oil feed and upgraded bearings resolved most issues. Regular oil and coolant changes, proper fuel system maintenance, and use of zinc-containing oil for the flat-tappet camshaft are essential for longevity. Well-cared-for examples can exceed 200,000 km.
The primary issues are main bearing wear on pre-1979 units, K-Jetronic fuel system failures (warm-up regulator, fuel distributor), and valve train wear if non-zinc oils are used. Cooling system component failure (hoses, thermostat, pump) is also common with age. These are documented in Mercedes-Benz service literature and owner maintenance reports.
The M 117.983 was used in the W116 450 SE, 450 SEC, and the flagship 450 SEL 6.9 (1977–1981). It was the standard 4.5L V8 petrol engine for these models during its production run, offering a balance of smooth power and luxury refinement in flagship sedans and long-wheelbase limousines.
Yes, but within limits. Performance tuning typically involves upgrading to performance camshafts, exhaust headers, or electronic fuel injection retrofits. Some owners install later KE-Jetronic systems for improved drivability. However, the engine's 8.8:1 compression and SOHC design cap significant power gains. Most modifications focus on improving throttle response and reliability rather than high output.
Fuel economy is modest by modern standards. In a W116 450 SEL 6.9, expect approximately 18–22 L/100km (16–13 mpg UK) in mixed driving. Highway cruising is more efficient at around 16 L/100km (18 mpg UK), while city driving can exceed 24 L/100km (12 mpg UK). K-Jetronic tuning and driving style significantly affect consumption.
No. The M 117.983 is a non-interference engine. If the timing chain fails, the pistons will not contact the valves, preventing catastrophic internal damage. However, a broken chain will still disable the engine and require significant repair. The double-row chain is durable but should be inspected periodically, especially on high-mileage engines.
Mercedes-Benz specified SAE 20W-50 mineral oil meeting API SE/CC standards. Modern equivalent oils with zinc (ZDDP) additives are recommended to protect the flat-tappet camshaft. Oil should be changed every 6,000 km or annually to ensure optimal valve train lubrication and engine longevity.
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