The 2.5-liter BMW M30B25 is the smallest member of the M30 inline-six family. It appeared in 1968 in the E3 2500 sedan and was produced in carburetor and fuel-injected versions until 1987.
Like all M30 engines, it has a cast-iron block, an aluminum 12-valve head with a single chain-driven camshaft and no hydraulic lifters. The original carburetor M30B25V was fed by two Zenith 35/40 INAT carburetors and produced 150 PS. In 1981 it received Bosch L-Jetronic injection: power stayed the same, while torque grew to 215 Nm. The bore is 86 mm and the stroke a short 71.6 mm.
The M30 family also includes: M30B28, M30B30, M30B33 and M30B35 / M30B34.
Specifications
| Production years | 1968-1987 |
| Displacement, cc | 2494 |
| Fuel system | carburetor / injector |
| Power output, hp | 145 – 150 |
| Torque output, Nm | 210 – 215 |
| Cylinder block | cast iron R6 |
| Block head | aluminum 12v |
| Cylinder bore, mm | 86 |
| Piston stroke, mm | 71.6 |
| Compression ratio | 9.0 – 9.6 |
| Features | SOHC |
| Hydraulic lifters | no |
| Timing drive | chain |
| Phase regulator | no |
| Turbocharging | no |
| Fuel type | petrol |
The engine was installed on:
- BMW E3 in 1968 – 1977 (2500);
- BMW E9 in 1974 – 1975 (2.5 CS);
- BMW 5-Series E12 in 1973 – 1981 (525);
- BMW 5-Series E28 in 1981 – 1987 (525i);
- BMW 7-Series E23 in 1981 – 1986 (725i).
Disadvantages of the BMW M30B25 engine
- Even after brief overheating the cylinder head can warp;
- After a rebuild the block often cracks around the cylinder head bolt threads;
- There are no hydraulic lifters: valve clearances need adjusting every 10-20 thousand km, and the adjusters themselves wear out;
- Carburetor versions need competent adjustment, and spare parts for them are getting scarce.
