BMW N43, N45 and N46 Four Cylinder Valvetronic Engines

BMW N43 engine

N43B20 showing twin catalytic converters.

Chronology

BMW had pioneered Valvetronic technology on the N42 engine, it's worth reading that page first to understand the system. It was succeeded in 2004 by the N46 two litre and N45 1600cc.

The N45 1.6 was designed as a lower cost, lower performance engine. It did not have Valvetronic and powered only the E81 116i, it had one very special two litre version. In order to homologate the racing car in 2006 BMW produced a limited edition E90 320Si four door saloon with 174bhp, this needed the non-Valvetronic valve gear to make more power at high rpm.

The N46 was used widely throughout the model range from 2004 until 2012. It was a two litre with Valvetronic. Over various model years it saw service in the E81 120i, E90 320i, E60 520i, X1, X3 and Z4. A detuned version (but still two litre) was available in the E87 116i, 118i and E90 318i. In 2006 an N46N was brought in which raised power to almost 170bhp in the E87 120i and E90 320i, but no change for it's still detuned "1.8" two litre version.

An 1800cc N46 powered the 2003-2005 E46 316i/ti until the E90 three series started.

In 2007 the N43 entered service, it had Valvetronic and direct fuel injection. It replaced the N45 which died with the pre-facelift E81 one series. It was available from 2008 as a 1600 in the E87 116i and E90 316i. A detuned 2.0 was sold int the E87 118i. The full 2.0 powered the E87 120i, E90 320i and E60 520i. Versions carried on until 2011 or possibly 2012 in some models.

The reason both N46N and N43s sold at the same time was sulphur. In some countries there's more sulphur in fuel that in others, these markets were unsuitable for the direction injection in the M43 so were sold the N46N instead. Direct injection is desirable as it's more fuel efficient, by up to 23% in this case.

BMW N43 engine

A very clean and tidy N43.

Design

There had been a version of the N42 without Valvetronic, the 1600cc N40. It was only sold in markets with a harsh tax regime. The N45 was a derivative of this engine using similar technology. The unit had twin balancer shafts and VANOS.

The N46 was a development of the N42 and had Valvetronic, VANOS and twin balancer shafts of a new design. This engine had DISA variable length intake technology on the two litre version (including those detuned engines sold as 1.8s) but the 1800cc block didn't. Compared to th N42 there were changes to the vacuum pump, conrods and the roller gear in the valve train.

The N64N produced the same power in the detuned edition but 20bhp more in the normal trim. This was mainly due to updated engine management, a new Bosch Motronic version.

The N43 was very similar to the N46N but had direction fuel injection for countries with suitable low sulphur petrol.

Variants

Code Size Power
bhp@rpm
Torque
lb/ft@rpm
BHP/
litre
Torque/
litre
Made Bore x
Stroke
Timing Weight
(kg)
VANOS
N43 1.6

1.8

2.0

121 @ 6000

143 @ 6000

170 @ 6700

118 @ 4250

139 @ 4250

154 @ 4250

76

72

85

74

70

77

2007-11 84x72

84x90

84x90

Chain 103 VANOS,
Valvetronic,
direct inj.
N45 1.6

2.0

115 @ 6000

173 @ 7000

110 @ 4300

155 @ 4250

72

87

69

77

2004-11 84x72

84x90

Chain 79 (short) VANOS, no
Valvetronic
N46

N46

N46N

1.8

2.0

2.0

115 @ 5500

150 @ 6200

170 @ 6400

129 @ 3750

147 @ 3750

154 @ 3750

63.9

75

85

72

73.5

77

2003-05

2004-06

2006-11

84x81

84x90

84x90

Chain 96 VANOS,
Valvetronic

 

BMW N46 engine

N46 hidden deep in a 120i.

Problems

There was a recall on ignition coils For the N43 direction injection engine after many owners suffered failures. It seems other German manufacturers have had similar issues with DI engines, doubtless the same parts supplier.

Engine failures have been seen due to missed oil changes or a cheap grade of oil being used. The correct oil is expensive and some garages skimp. Combine this with very long (too long!) service intervals and the result is blocked oil passages or oil starvation. Best practice is to service every 10,000 miles with good oil. If you buy one of these do an oil flush with Winns before change the oil.

Worn timing chains have been seen but with less frequency than on the N42 (see N42 page).

The N43's direct injectors seem to have a shorter life than conventional injectors, many owners had had to replace them.

The CCV / OSV oil separator valve issues on the older N42 seem to be less common on these engines.