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BMW N42B20 Engine (Specs, Reliability & Issues)

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BMWs N42B20 engine is a 2L inline-4 cylinder engine producing 143hp and 200nm of torque.

The M43B18, M43TU, and M44B19 engines were all replaced by this N42B20 two-litre inline 4-cylinder engine, which debuted in 2001.

In this article, we’ll go over the design and specs of the BMW N42B20 engine, as well as its reliability and issues.

Design of the BMW N42B20 Engine

The N42B20 engine has an aluminium cylinder block with cast iron sleeves instead of a completely cast iron cylinder block.

As a consequence, the engine is much lighter than previous BMW four-cylinder engines. New 90 mm stroke crankshaft, pistons, and connecting rods are installed within the cylinder block.

bmw N42B20 engine

The N42B20 engine’s balancing shafts are identical to the M43TU engine’s. To accommodate them into the new cylinder block, engineers had to make a few modest changes.

A 16-valve DOHC aluminium cylinder head sits above the new aluminium cylinder block.

This is a huge development above predecessors, which featured 8-valve SOHC heads.

  • Intake valves are 32 mm in diameter
  • Exhaust valves are 29 mm in diameter

The N42B20 camshaft has a valve lift of 9.7/9.7 mm and a duration of 250/258 degrees.

The engine employs Valvetronic, a variable valve lift technology. A timing chain is installed in the engine.

On both camshafts, the variable valve timing system is incorporated (Double-Vanos). The intake additionally has an electronically controlled variable shape intake manifold.

BMW coined the term DISA to describe this mechanism. It’s designed to provide the optimum torque and power characteristics at both high and low rpm.

Also offered is a Bosch DME ME9.2 fuel injection system.

The N42B20 engine was used in BMW 18i automobiles. Aside from that, the engine is a reduced-displacement 1.8L N42B18 engine.

The N42B20 engine was produced until 2004, when it was replaced by the newer N45B20S and N46B20 engines.

BMW N42B20 Engine Specs

  • Manufacturer: BMW Plant Hams Hall
  • Production years: 2001-2004
  • Cylinder block material: Aluminium
  • Cylinder head material: Aluminium
  • Fuel type: Gasoline
  • Fuel system: Fuel injection
  • Configuration: Inline
  • Number of cylinders: 4
  • Valves per cylinder: 4
  • Valvetrain layout: DOHC
  • Bore: 84.0 mm
  • Stroke: 90.0 mm
  • Displacement: 1995 cc
  • Type: Four-stroke, naturally aspirated
  • Compression Ratio: 10:1
  • Power: 143 hp (105 kW) at 6,000 rpm
  • Torque: 148 lb-ft (200 Nm) at 3,750 rpm
  • Firing order: 1-3-4-2
  • Engine oil weight: 5W-30, 5W-40
  • Engine oil capacity: 4.25 litres
  • Oil change interval: 6,000 miles (10,000 km) or 12 months
  • Applications: BMW E46 318i, 318Ci, 318ti

Problems and Reliability of the BMW N42B20

Listed below are some of the common problems associated with this engine.

  • Diesel sound: The timing chain isn’t quite dependable. It’s possible that the noise is caused by a stretched timing chain or its tensioner. The life of a timing chain is about 60,000 kilometres.
  • Ignition coils: Ignition coils are easily damaged when spark plugs are changed.
  • Overheating: Maintain the cooling system’s radiator condition. The engine will begin to consume oil after a brief period of overheating. The reason for this is because valve stem seals are prone to failure.

In addition, the N42B20 engine has strict requirements for oil quality. Use the manufacturer’s suggested engine oil.

The engine is packed with cutting-edge technology and electronics.

However, it has the same lifespan and dependability as the M40 and M43 series engines.

Tuning the BMW N42B20 Engine

Remapping is usually the go-to for most people when tuning, however there are a verity of paths you can go down in order to tune your N42B20.

  1. Fast road camshafts, sports exhaust manifolds, panel air filters, drilled and smoothed air boxes, intake headers, and remaps/piggyback ECUs are all common stage 1 upgrades.
  2. Induction kit, sports catalyst & performance exhaust, ported and polished head, fuel pump modifications, and high flow fuel injectors are all common stage 2 mods.
  3. Twin charging conversions, engine balancing and blueprinting, internal engine enhancements (head flowing porting/bigger valves), competition cam, crank, and piston changes to adjust compression, and adding or upgrading forced induction (turbo/supercharger) are all common stage 3 mods.


On the N42B20, the form and flow parameters of the air intake manifolds may have a significant impact on fuel atomisation.

Although some manufacturers supply fairly well flowing air intake manifolds, most need motorsport components.

Larger intake pipes, smoother pipework, and a cold air feed or ram air feed may help improve power.


Fast road cams are one of the most important mechanical upgrades, but they must be fitted by someone who understands what they’re doing, and they’re not always easy to come by.

Note that these modifications will not add power on their own in most circumstances, but they may aid boost power after other mods by eliminating the limitation.

Forced Induction

Forced induction is the most effective way to increase air supply, enabling you to burn more fuel and produce more power.

It is one of the most expensive enhancements, but it yields the greatest benefits.


Porting and flowing the head has the purpose of getting air into the engine while reducing flow constraints and turbulence.

Increasing the N42B20 valve size, adding some port matching, and head flowing will also enhance power, and as a bonus, you’ll be able to receive a bigger boost from other tuning tweaks.


Mapping should assist you in realising the full potential of all the components you’ve installed on your N42B20.

In certain circumstances, since the factory ECU is locked, flashing is not an option, therefore an aftermarket ECU is the way to go.

Many of these will exceed original ECUs but be sure it has knock protection and that it is correctly installed.

It will normally offer you roughly 30% more power on turbocharged cars and around 15% more power on naturally aspirated engines, but the final outcome will depend on the items you’ve installed and the state of your engine.



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  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer.He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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