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.
M30 family: M30B25, M30B28, M30B30, M30B33, M30B34, M30B35, M30B35LE.
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 |
| Recommended engine oil | 5W-30 |
| Engine oil capacity, liter | 5.5 |
| Fuel type | petrol |
| Weight, kg | 192 |
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), 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.
Frequently asked questions about the BMW M30B25
How much power does the BMW M30B25 make?
The BMW M30B25 develops 145 - 150 hp and 210 - 215 Nm of torque.
How much oil does the BMW M30B25 take and which one?
Engine oil capacity: 5.5 liters. Recommended oil: 5W-30.
Does the BMW M30B25 have a timing belt or chain?
The BMW M30B25 uses a timing chain.
Is the BMW M30B25 turbocharged?
No, the BMW M30B25 is naturally aspirated.
Does the BMW M30B25 need valve clearance adjustment?
Yes, there are no hydraulic lifters, so the valve clearances have to be checked and adjusted periodically.
What cars was the BMW M30B25 installed on?
BMW E3 in 1968 - 1977 (2500); BMW E9 in 1974 - 1975 (2.5 CS); BMW 5-Series E12 in 1973 - 1981 (525), 5-Series E28 in 1981 - 1987 (525i); BMW 7-Series E23 in 1981 - 1986 (725i).
What are the common problems of the BMW M30B25?
Even after brief overheating the cylinder head can warp. After a rebuild the block often cracks around the cylinder head bolt threads. All known problems.
