BMW N42 Four Cylinder Valvetronic Engine

BMW N42 engine

N42 in an E46 318ti Compact


When the E46 three series was launched the four cylinder petrol models used the M43 engine in 1.6 and 1.9 guises. Unlike the E36 it replaced there was no 16 valve alternative so the 318i was very much a budget model, you really needed a six to have any fun. That changed for the better in 2001 when the 1.8 and 2.0 16 valve N42 was introduced.

The new engine gave the 318i, 318Ci and 318ti over 20bhp more power and a good rise in torque which was badly needed. It transformed the car.

The N42 was replaced by the N46 in 2004. It was only ever used in the E46.

BMW N42 engine

Valvetronic valve operation with control motor highlighted


The big news was the introduction of BMW's Valvetronic system, this was the first engine to have it. Since the dawn of the petrol engine over 100 years before, a throttle plate had been used to control power by regulating the volume of air entering the combustion chambers. BMW changed all that.

With Valvetronic a new shaft is introduced next to the intake camshaft. This new shaft is controlled by an electric stepper motor mounted at right angles to it by means of a worm and sector gear. The shaft adjusts the position of the finger followers / rockers which are used by the intake camshaft to open the valves. By this means it can control the amount the intake valves open (the lift) and thus the amount of air which enters and cylinders, negating the need for a throttle plate. This reduces pumping losses, increases efficiency and quickens engine response.

Efficiency gains of about 10 percent over a normal engine are possible with Valvetronic, power gains at partial throttle are in the same range. But peak power is unchanged as there is little difference between a wide open throttle and fully open Valvetronic. Efficiency gains are seen only at partial throttle settings.

Nearly all new BMW engines, including turbos, are Valvetronic. Because the intake manifold of a turbocharged engine is always above atmospheric pressure, Valvetronic doesn't offer as big an advantage as in naturally aspirated engines. But it improves throttle response because the time taken for the turbo to pressurise the intake tract is reduced. Although red line on the N42 was 6500rpm Valvetronic can have issues at higher rpms so introduction in //M engines was slower. Around this time BMW experimented with electronically operated valves using solenoids and no camshafts at all, but the rev limit was too low.

Hand in hand with Valvetronic go BMW's existing VANOS variable valve timing and DISA variable length intake tract technologies. These all come together to optimise performance under different engine speeds and loads. This is an engine where the ECU has it's work cut out!

There are down sides with Valvetronic however. Because the throttle plate doesn't create a vacuum in the intake manifold a separate vacuum generator must be fitted. Vacuum is needed for the brake booster and emission systems. This and the extra weigh of all the new parts makes for a heavier engine.

Paradoxically there is still a normal throttle body fitted, as can be seen below on the N42 picture below. It's controlled electronically by the ECU and is fully open under most driving conditions. It partially closes when the engine first starts to create initial vacuum but also doubles as an emergency system in case the Valvetronic control motor fails (sticking open could be nasty).

BMW N42 engine

N42 with secondary throttle on upper right


Code Size Power
Manufactured Bore x
Timing Weight
VANOS Used in
N42 1.8


113 @ 5500

140 @ 6000

129 @ 3750

147 @ 3750





2001 - 2004 84x81


Chain 100 Valvetronic + VANOS E46 316i

E46 318i


BMW N42 engine

View of the N42's intervals


The biggest problem with this engine was worn timing chains. The original tensioner piston was too short and allowed the chain to be slack which caused wear to the guides, chain and sprockets. The revised tensioner is longer and should be fitted to all engines as a precaution. Worn chains can skip a tooth or two causing running issues and eventually a dead engine. A worn chain will sound rattly, especially when cold.

Oil leaks weren't uncommon at the spark plug valve cover seals, VANOS seals and vacuum pump. You'd think the spark plug oil seal problem would have been fixed since it was first observed ten years earlier on the M42.

The crank case ventilation (CCV) also called the oil separator valve (OSV) was a device forced on many manufacturers in the drive for lower emissions. They can clog up, especially on an engine that does a lot of short journeys in a cold climate. Symptoms of a clogged one include rough idle, high oil consumption, hard to start when cold, stalling and lack of power at low revs. BMW made an insulated version for very cold climates. You need to remove the intake manifold to fit a new one and some of the bolts are hard to access.