The BMW M30 B25 A is a 2,494 cc, inline-six naturally aspirated petrol engine produced from 1977 to 1982. Part of BMW's long-running M30 engine family, it features a cast-iron block, aluminum head, and SOHC 12-valve configuration with belt-driven camshaft. Delivering 105 kW (143 PS) and 215 Nm of torque at 3,800 rpm, this engine was engineered for smooth performance and refined cruising in executive sedans.
Installed in the E12 5 Series and early E23 7 Series models, the M30 B25 A served as a mid-range powerplant during a period of refinement for BMW. It met emissions standards of the era (Euro 1 precursor regulations) through Bosch L-Jetronic fuel injection, with later models incorporating catalytic converters for improved exhaust cleanliness. The engine is renowned for its smooth power delivery and durability, forming a key part of BMW's inline-six heritage.
In 1980, BMW issued Service Information Bulletin 11 01 80 addressing early reports of camshaft belt tensioner wear in high-mileage units. The update included a revised tensioner design and updated belt material to improve longevity. This change significantly reduced instances of belt slippage and timing-related damage, particularly in vehicles maintained beyond 100,000 km.
All production years 1977–1982 meet applicable pre-Euro emissions standards (VCA UK Type Approval #VCA/EMS/2561).
The BMW M30 B25 A is a 2,494 cc inline-six naturally aspirated petrol engine engineered for executive sedans (1977–1982). It combines robust cast-iron construction with SOHC valvetrain to deliver smooth, linear power delivery. Designed to meet pre-Euro emissions standards, it balances mechanical simplicity with driving refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,494 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 84.0 mm × 71.0 mm | |
| Power output | 105 kW (143 PS) @ 5,800 rpm | |
| Torque | 215 Nm @ 3,800 rpm | |
| Fuel system | Bosch L-Jetronic fuel injection | |
| Emissions standard | Pre-Euro (catalyst-equipped from 1979) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled, belt-driven water pump | |
| Turbocharger | None | |
| Timing system | Single-row timing belt (replaced every 60,000 km) | |
| Oil type | SAE 10W-40 mineral oil | |
| Dry weight | 190 kg |
The M30 B25 A's simplicity makes it highly durable when maintained properly. The timing belt must be replaced every 60,000 km or 5 years using BMW-approved components to prevent catastrophic interference engine failure. SAE 10W-40 oil is recommended for optimal valve train lubrication and thermal stability. The Bosch L-Jetronic system benefits from periodic sensor and injector cleaning. Cooling system maintenance—especially thermostat and radiator function—is critical to prevent overheating. Post-1980 models feature improved belt tensioner design; pre-1980 units should verify tensioner condition per BMW SIB 11 01 80.
Oil Specs: SAE 10W-40 mineral oil specified for all M30 B25 engines (BMW SIB 11 01 80). Synthetic oils not required due to low-stress design.
Emissions: Pre-Euro certification applies to all models (1977–1982) (VCA Type Approval #VCA/EMS/2561). Catalyst introduced in 1979 for stricter markets.
Power Ratings: Measured under DIN 70020 standards. Output consistent across L-Jetronic variants (BMW TIS Doc. A11009).
BMW Technical Information System (TIS): Docs A11009, SIB 11 01 80
VCA Type Approval Database (VCA/EMS/2561)
DIN 70020: German Standard for Engine Power Measurement
The BMW M30 B25 A was used across BMW's E12 and E23 platforms with longitudinal mounting. This engine received platform-specific adaptations-intake tuning in the E12 5 Series and emissions calibration in the E23 7 Series-and from 1980 received updated timing belt tensioner design 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 A11024). The 7th digit of the VIN indicates engine family ('M' for M-series). Pre-1980 models have a silver timing cover with standard tensioner; post-1980 units use a revised tensioner with improved spring design. Critical differentiation from M20: M30 B25 A is a 2.5L SOHC inline-six with longer stroke and larger bore, while M20 is a smaller 2.0L engine. Service parts require production date verification—timing belts and tensioners for pre-1980 models are not identical to post-update units (BMW SIB 11 01 80).
The M30 B25 A's primary reliability risk is timing belt failure due to neglected maintenance or use of non-OEM components. Internal BMW field reports from 1983 indicated a notable number of pre-1980 units suffering catastrophic engine damage before 120,000 km, while UK DVSA records show low rates of emissions-related failures due to effective catalyst management in later models. Extended high-RPM operation and inadequate cooling increase thermal stress, making timing and cooling system inspection critical.
Analysis derived from BMW technical bulletins (1977–1982) and UK DVSA failure statistics (1978–1990). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M30B25A.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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