M40
The BMW M40 is a 4-cylinder engine, fitted to the 316i and 318i after 1987. It replaced the M10 as the standard 4-cylinder engine in 1987.
Contents
History
The M40B16 was also fitted to the E36. The M40B18 was also fitted to the E34 from 1988 to 1994, and briefly the E32 in 1992-1993.
Versions
| Engine | Displacement | Power | Torque | Redline | Year |
|---|---|---|---|---|---|
| M40B16 | 1.6 L (1596 cc/97 in³) | 75 kW (101 hp) @ 5500 | 143 N·m (105 ft·lbf) @ 4250 | 6200 | 1988 |
| 73 kW (98 hp) @ 5500 | 141 N·m (104 ft·lbf) @ 4250 | 6200 | 1988 | ||
| M40B18 | 1.8 L (1796 cc/109 in³) | 85 kW (114 hp) @ 5500 | 165 N·m (122 ft·lbf) @ 4250 | 6200 | 1987 |
| 83 kW (111 hp) @ 5500 | 162 N·m (119 ft·lbf) @ 4250 | 6200 | 1987 |
Components
The engine in all E30s is a three-part design, featuring a main Block with a Sump at the bottom and a Head at the top.
Sump
The M40 Sump is a two part design with an upper and lower sump. The upper part bolts directly to the block, sealed with a gasket, and the lower sump then bolts to the upper.
Leaks in this area are normally due to upper bolts coming loose, despite their torque rating. Because some of these bolts are only accessible with the lower sump removed, the two parts have to be disassembled to cure the leak. When removing the lower sump, don't be surprised to find a bolt sitting in the oil that has come out completely from the upper sump.
Oil Pump
Sump Gasket
Block
Crankshaft
Piston Rods
Piston Head
Piston Rings
Crank Pulley
Head
Rocker Cover
Despite the three styles of Head, the rocker cover is interchangeable across all M40 engines. It is positioned on 8 studs and fixed with M10 nuts. It has one hole for the Oil Cap, and one port for the breather hose.
When removing and replacing the rocker cover, it is worth replacing the rocker cover gasket.
Cam
Valves
Rocker Arms
Head Gasket
Breather Hose
To balance the pressure inside the head, a rubber hose runs from the top of the rocker cover to the throttle body.
Ancilliaries
Flywheel
Starter Motor
Engine Mounts
Servicing
Main article: Basic M40 Servicing
Every engine needs its fluids and filters changed regularly. The M40 engine also needs its timing belt replaced at regular intervals. Learn more about changing the timing belt.
Common Problems
Won't Rev Over 5000
Unfortunately, this is a common sign of engine wear, and indicates a worn out cam shaft. The problem can be diagnosed in two ways. If the engine sound can be described as "sounding like a skeleton wanking in a dustbin" then your cam is very likely worn.
To confirm, remove the rocker cover and baffle plate so that you have access to the cam shaft, and run your finger nail over the cam lobes. If you can feel scatches, grooves or other imperfections, the cam is in bad condition.
The only solution is to replace.
