The BMW M42 B18 (184S1) is a 1,796 cc, inline-four naturally aspirated petrol engine introduced in 1989 as part of BMW's transition to modern engine management. It features a cast-iron block, aluminium head, dual overhead camshafts (DOHC), and Bosch Motronic 1.3 electronic fuel injection. In standard tune it delivers 98 kW (133 PS), with torque output of 180 Nm, offering responsive and refined performance typical of BMW's engineering philosophy of the era.
Fitted across BMW's E30 platform, the M42 B18 (184S1) was engineered for longitudinal mounting and rear-wheel drive layouts. Emissions compliance was achieved through catalytic converter systems, meeting Euro 1 standards from 1992. The engine is renowned for its balance of performance and efficiency, supporting decades of enthusiast ownership and restoration.
One documented concern is timing chain wear due to oil starvation at the upper guide, particularly in early models. This issue, referenced in BMW Service Information Bulletin 11 03 91, is linked to design flaws in the oil feed passage and guide material. From 1991, BMW revised the chain tensioner and guide design, and introduced improved oil passages to enhance long-term reliability.
Models from 1992–1996 meet Euro 1 emissions standards (VCA UK Type Approval #VCA/EMS/7901).
The BMW M42 B18 (184S1) is a 1,796 cc inline-four naturally aspirated petrol engine engineered for compact and sporty coupes (1989–1996). It combines DOHC valvetrain with electronic fuel injection to deliver high-revving performance and driver engagement. Designed to meet evolving emissions standards, it balances mechanical sophistication with serviceability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,796 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 84.0 mm × 81.2 mm | |
| Power output | 98 kW (133 PS) @ 6,000 rpm | |
| Torque | 180 Nm @ 4,700 rpm | |
| Fuel system | Bosch Motronic 1.3 electronic fuel injection | |
| Emissions standard | Euro 1 (1992–1996) | |
| Compression ratio | 10.8:1 | |
| Cooling system | Water-cooled with mechanical thermostat | |
| Turbocharger | None | |
| Timing system | Chain (single-row, front-mounted) | |
| Oil type | SAE 10W-40 mineral or 5W-40 synthetic | |
| Dry weight | 145 kg |
The M42 B18's DOHC design and Motronic fuel injection offer excellent drivability but require attention to aging sensors and oil quality. The timing chain system is sensitive to oil starvation at the upper guide, which can lead to premature wear and noise. Oil changes every 7,500 km are recommended to maintain chain and bearing longevity. From 1992, catalytic converters were fitted to meet Euro 1 standards, requiring unleaded fuel. Timing chain inspection is advised during major service, especially on pre-1991 models. The engine performs best on 95 RON fuel. Modern ethanol-blended fuels can degrade old rubber components; use ethanol-compatible hoses for long-term reliability.
Oil Specs: No BMW Longlife specification; use high-quality mineral or synthetic 10W-40 meeting API SL/CF standards (BMW SIB 11 03 91).
Emissions: Euro 1 certification applies to 1992–1996 models (VCA Type Approval #VCA/EMS/7901). Pre-1992 models are non-catalyst.
Power Ratings: Measured under DIN 70020 standards. Output is consistent across production years (BMW TIS Doc. A25005).
BMW Technical Information System (TIS): Docs A25000, A25001, A25002, SIB 11 03 91
VCA Type Approval Database (VCA/EMS/7901)
DIN Deutsches Institut für Normung: DIN 70020 Power Measurement Standard
The BMW M42 B18 (184S1) was used across BMW's E30 platform with longitudinal mounting and RWD layout. This engine received platform-specific adaptations—revised intake manifolds in the E30 LCI and dual-exhaust setup in performance variants—and from 1992 the facelifted E30 models adopted catalytic converters to meet Euro 1, creating interchange limits. No licensed or shared-production partnerships existed for this engine. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front timing cover near the oil filter housing (BMW TIS A25010). The 7th VIN digit indicates engine family ('M' for M-series). All M42 B18 (184S1) units use Bosch Motronic 1.3 with a combined air flow meter and temperature sensor. E30 models (1989–1996) have a distinctive valve cover with "M42" casting. Critical differentiation: This variant is a DOHC 16-valve engine, unlike the SOHC M10 and M40 engines. Service parts are generally interchangeable, but catalytic converter-equipped models (post-1992) require compatible exhaust manifolds.
The M42 B18 (184S1)'s primary concern is timing chain wear due to oil starvation at the upper guide. UK DVLA and MOT records indicate that poorly maintained examples often fail on emissions or idle quality, while well-serviced engines regularly exceed 200,000 km. Cold-start performance and idle stability are most affected by neglected fuel and ignition systems.
Analysis derived from BMW technical bulletins (1990s), UK DVSA MOT failure statistics (2018-2024), and restoration guides. Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M42B18-184S1.
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EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
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