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BMW M40B18 Engine (Design, Issues & Tuning)

Updated: Feb 2

✔ This article has been fact checked.

BMW created the M40B18, a SOHC straight-four petrol engine, between 1987 and 1994. It has a displacement of 1.8L producing between 111-114hp and 162-165nm depending on the version.

It has a bore of 84 mm and a stroke of 81 mm. M40 engines were used to replace the original M10-series engines, which were well-liked and successful in BMW cars at the time.

This engine was used in the following cars.

  • 1987-1994 E30 318i

  • 1988-1994 E34 518i

  • 1992-1993 E36 318i

Table of Contents:

m40b18 engine

BMW M40B18 Engine Design

The engine is conventional and basic. Cast iron makes up the cylinder block. The cylinder head contains a SOHC 8-valve aluminium cylinder head with hydraulic lifters. The duration and valve lift of the M40B18 camshaft are 244/244 degrees (single pattern) and 10.6/10.6 mm.

In contrast to M10 engines, M40 engines use a timing belt rather than a chain.

The engine has electronic fuel injection and ignition as well as an aluminium intake manifold. Fuel injection systems utilised in E30 vehicles are Bosch Motronic 1.3 and Bosch Motronic 1.7 are used in E36 variants.

The 18i variations are covered under the M40B18 application. Since BMW had already invested two years in creating a successor engine, the M43B18, manufacture of this engine was stopped in 1994.

Engine Specs

  • 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 & Issues

Below is a list of the various issues a M40B18 engine may encounter.

  • Timing belt: It quickly degrades and is a common reason why valves bend. Keep an eye on the timing belt's condition. 

  • Knocking & ticking: Any broken camshaft must be replaced to prevent future costly repairs and knocking and ticking noises. In the event that the camshaft is worn out, the engine won't be able to rev high.

  • Electrical components: Engines like the M40B18 have outdated electrical components. If your idle is unsteady or you're having acceleration issues, check the air flow and oxygen sensors.

  • Fuel injectors: Dirty injectors are a typical issue that lead to excessive fuel use and power lo