The BMW N42 was an inline four-cylinder petrol engine that was available from 2001 to 2004. The N42 replaced BMW’s M43 engine and won the International Engine of the Year Award in 2001.
The N42 engine had an aluminium alloy block and cylinder head, two gear-driven balance shafts, double overhead camshafts (chain-driven), variable intake and exhaust valve timing (BMW’s double VANOS), four valves per cylinder, variable intake valve lift (BMW’s Valvetronic), Bosch Motronic ME 9.2 engine management and a maximum engine speed of 6500rpm.
The N42 engine was also fitted with a variable intake manifold (BMW’s Differentiated Intake System, or DISA) which enabled intake pipe length to be adjusted according to engine speed for more efficient cylinder filling and scavenging.
| Engine | Capacity | Peak power | Peak torque | Models | Years |
|---|---|---|---|---|---|
| N42B18 | 1796 cc (84.0 x 81.0) |
85kW at 5500rpm | 175Nm at 3750rpm | E46 316i, E46 316ti |
2001-04 |
| N42B20 | 1995 cc (84.0 x 90.0) |
105kW at 6000rpm | 200Nm at 3750rpm | E46 318i, E46 318ti |
2001-04 |
N42 faults: chain tensioners and oil leaks
The original timing chain tensioners could wear prematurely and slacken. If this occurred, the chain may slip and jump one tooth at a time, adversely affecting the exhaust camshaft timing. If the chain slips, this will also cause the chain guides to break as the surface comes into contact with the chain – this makes it more likely than the chain will jump. At worst, the change in exhaust camshaft timing can cause the valves to hit the piston crowns such that the valve rods bend – if this occurs, the engine will need to be rebuilt. If the chain jumps, diagnostics may indicate a camshaft sensor fault. It is understood that BMW introduced redesigned, longer chain tensioners in 2003 – these tensioners could be identified by their smaller heads. For preventive maintenance, it is common for the original tensioners to be replaced with the redesigned tensioners.
The N42 engine was susceptible to oil leaks from the rocker cover gaskets, top profile gaskets and VANOS solenoid seals.
