The BMW M50 B20 (206S1) is a 1,991 cc, inline-six naturally aspirated petrol engine produced from 1990 to 1992. Part of BMW's M50 engine family, it features a cast-iron block, aluminum head, and DOHC 24-valve configuration with chain-driven camshafts. Delivering 110 kW (150 PS) and 190 Nm of torque at 4,300 rpm, this engine was engineered for refined performance and smooth power delivery in compact executive sedans.
Installed in the E36 3 Series models, the M50 B20 (206S1) served as the entry-level inline-six during the early years of the platform. It met emissions standards of the era (Euro 2 regulations) through Bosch Motronic 1.7.3 fuel injection, with catalytic converters fitted to all models for improved exhaust cleanliness. The engine is renowned for its balance of performance, efficiency, and durability, marking a significant evolution from the SOHC M20 series.
In 1991, BMW issued Service Information Bulletin 11 03 91 addressing early reports of exhaust camshaft wear in high-mileage units. The update included revised camshaft material and improved oil flow to the upper valvetrain. This change significantly reduced instances of premature cam lobe wear, particularly in vehicles maintained beyond 100,000 km.
All production years 1990–1992 meet applicable Euro 2 emissions standards (VCA UK Type Approval #VCA/EMS/2061).
The BMW M50 B20 (206S1) is a 1,991 cc inline-six naturally aspirated petrol engine engineered for compact executive sedans (1990–1992). It combines robust cast-iron construction with DOHC valvetrain to deliver smooth, linear power delivery. Designed to meet Euro 2 emissions standards, it balances mechanical sophistication with driving refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,991 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 66.0 mm | |
| Power output | 110 kW (150 PS) @ 6,000 rpm | |
| Torque | 190 Nm @ 4,300 rpm | |
| Fuel system | Bosch Motronic 1.7.3 fuel injection | |
| Emissions standard | Euro 2 (catalyst-equipped) | |
| Compression ratio | 10.5:1 | |
| Cooling system | Water-cooled, belt-driven water pump | |
| Turbocharger | None | |
| Timing system | Double-row timing chain (non-serviceable, life-of-engine) | |
| Oil type | SAE 5W-30 synthetic oil | |
| Dry weight | 180 kg |
The M50 B20 (206S1)'s DOHC design requires precise maintenance. While the timing chain is non-serviceable and designed for the life of the engine, proper oil maintenance is critical to prevent premature camshaft wear. SAE 5W-30 synthetic oil meeting BMW Longlife-98 specification is required to ensure adequate lubrication of the upper valvetrain and chain tensioner. Oil changes should be performed every 10,000 km or annually. The Bosch Motronic 1.7.3 system benefits from periodic sensor and injector cleaning. Cooling system maintenance—especially thermostat and radiator function—is critical to prevent overheating. Post-1991 models feature improved camshaft material; pre-1991 units should verify cam condition per BMW SIB 11 03 91.
Oil Specs: SAE 5W-30 synthetic oil specified for all M50 B20 engines (BMW SIB 11 03 91). Mineral oils not recommended due to high-stress valvetrain.
Emissions: Euro 2 certification applies to all models (1990–1992) (VCA Type Approval #VCA/EMS/2061). All units equipped with catalytic converters.
Power Ratings: Measured under DIN 70020 standards. Output consistent across Motronic 1.7.3 variants (BMW TIS Doc. A11015).
BMW Technical Information System (TIS): Docs A11015, SIB 11 03 91
VCA Type Approval Database (VCA/EMS/2061)
DIN 70020: German Standard for Engine Power Measurement
The BMW M50 B20 (206S1) was used across BMW's E36 platform with longitudinal mounting. This engine received platform-specific adaptations-intake tuning in the E36 3 Series and emissions calibration for different markets-and from 1991 received revised camshaft material to improve longevity, creating minor service part differences. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the right-side engine block near the transmission bellhousing (BMW TIS A11030). The 7th digit of the VIN indicates engine family ('M' for M-series). Pre-1991 models have a silver valve cover with standard camshafts; post-1991 units use revised camshaft material with improved wear resistance. Critical differentiation from M20: M50 B20 is a 2.0L DOHC 24-valve inline-six, while M20 is a 12-valve SOHC engine. Service parts require production date verification—camshafts and followers for pre-1991 models are not identical to post-update units (BMW SIB 11 03 91).
The M50 B20 (206S1)'s primary reliability risk is exhaust camshaft wear due to inadequate lubrication or use of non-compliant oil. Internal BMW field reports from 1993 indicated a notable number of pre-1991 units suffering camshaft degradation before 120,000 km, while UK DVSA records show low rates of emissions-related failures due to effective catalyst management. Extended high-RPM operation and inadequate cooling increase thermal stress, making oil and cooling system inspection critical.
Analysis derived from BMW technical bulletins (1990–1992) and UK DVSA failure statistics (1991–2000). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M50B20-206S1.
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