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BMW M40B18 Engine (Specs, Reliability & Issues)

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Last Updated on: 16th November 2023, 01:59 am

BMWs M40B18 engine is a 1.8-liter four-cylinder engine, the M40-series commenced production in 1987.

The original M10-series engines, which were popular and successful in BMW automobiles at the time, were replaced with M40 engines.

A year later, the 1.6-liter M40B16 engine was released, which was a smaller variation.

In this article, we’ll discuss the design of the BMW M40B18 engine, as well as its reliability and issues.

Design of the BMW M40B18 Engine

The engine is simple and traditional. The cylinder block is made of cast iron. A SOHC 8-valve aluminium cylinder head with hydraulic lifters is housed within the cylinder head.

The M40B18 camshaft has a duration of 244/244 degrees (single pattern) with a valve lift of 10.6/10.6 mm.

bmw M40B18 engine

M40 engines, unlike M10 engines, utilise a timing belt rather than a chain. An aluminium intake manifold, as well as electronic fuel injection and ignition, are included in the engine.

The Bosch Motronic 1.3 fuel injection system is used in E30 cars, whereas Bosch Motronic 1.7 is used in E36 variants.

The M40B18 application covers the 18i variants. The production of this engine was discontinued in 1994 since BMW had previously spent two years developing a replacement engine, the M43B18.


  • Manufacturer: Steyr Plant
  • Production years: 1987-1994
  • Cylinder block material: Cast Iron
  • Cylinder head material: Aluminium
  • Fuel type: Gasoline
  • Fuel system: Fuel injection
  • Configuration: Inline
  • Number of cylinders: 4
  • Valves per cylinder: 2
  • Valvetrain layout: SOHC
  • Bore: 84.0 mm
  • Stroke: 81.0 mm
  • Displacement: 1796 cc
  • Type of internal combustion engine: Four-stroke, naturally aspirated
  • Compression Ratio: 9:1
  • Power: 113 hp at 5,500 rpm
  • Torque: 120 lb-ft (160 Nm) at 4,250 rpm
  • Firing order: 1-3-4-2
  • Engine oil weight: 5W-30, 5W-40, 10W-40, 15W-50
  • Engine oil capacity: 4.0L
  • Oil change interval: 6,000 miles (10,000 km) or 12 months
  • Applications: BMW 318i E30, BMW 318i E36, BMW 518i E34

Reliability and Issues

There are a fair few issues with the M40B18 engine, as listed below.

1. Timing Belt

It rapidly wears out and is a typical cause of bending valves. Keep an eye on the condition of the timing belt.

2. Knocking and Ticking Sounds

Any damaged camshaft must be replaced to avoid an expensive repair in the future. The engine will not be able to rev high if the camshaft is worn out.

3. Electrical Components

Old electrical components may be found in engines like the M40B18. Check the air flow and oxygen sensors if your idle is unstable or you’re experiencing acceleration problems.

4. Dirty Injectors

Dirty injectors are a common problem, resulting in excessive fuel use and power loss. This may be resolved by replacing the injectors.

5. Overheating

Overheating is a problem with the M40, as it is with all BMW engines. Remember to clean the radiator and replenish the coolant in the system according to your car’s maintenance schedule.

6. Milage and Age

The M40B18 engine has a service life of 180,000 miles. In and of itself, the engine is reliable, but locating a car with that engine and low miles may be tough.


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 M40B18.

  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 M40, the form and flow parameters of the air intake manifolds may have a significant impact on fuel atomisation.

Although some manufacturers supply fairly 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 M40 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 M40.

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 aftermarket ECUs 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.

However, the final outcome in terms of power output 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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