The BMW B42 S20 A is a 1,998 cc, inline-four naturally aspirated petrol engine produced between 2015 and 2020.
It forms part of BMW's modular B-series engine family, designed primarily for compact and subcompact vehicles with transverse mounting.
Featuring double overhead camshafts (DOHC), Valvetronic III variable valve lift, and direct fuel injection (High Precision Injection), it delivers 100 kW (136 PS) at 6,500 rpm with peak torque of 200 Nm at 4,400 rpm.
This engine was engineered for reliability and smooth power delivery, targeting entry-level models where turbocharging complexity and cost were not justified.
All B42 S20 A engines meet Euro 6a emissions standards (VCA UK Type Approval #VCA/EMS/8812).
The BMW B42 S20 A is a 1,998 cc inline-four naturally aspirated petrol engine engineered for transverse-mounted compact models (2015–2020). It combines High Precision Injection with Valvetronic III to deliver linear power delivery and responsive throttle characteristics. Designed to meet Euro 6a emissions standards, it prioritizes reliability and serviceability over high specific output.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,998 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve, Valvetronic III | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 82.0 mm × 94.6 mm | |
| Power output | 100 kW (136 PS) @ 6,500 rpm | |
| Torque | 200 Nm @ 4,400 rpm | |
| Fuel system | High Precision Injection (direct injection, up to 200 bar) | |
| Emissions standard | Euro 6a | |
| Compression ratio | 11.0:1 | |
| Cooling system | Water-cooled | |
| Timing system | Dual chain (primary and secondary) | |
| Oil type | BMW Longlife-01 (SAE 5W-30) | |
| Dry weight | 132 kg |
The naturally aspirated design with Valvetronic III provides predictable, linear power delivery ideal for urban and light highway use but requires high-revving operation to reach peak output. BMW Longlife-01 (5W-30) oil is essential for maintaining Valvetronic system longevity and preventing premature wear. The dual-chain timing system is robust but sensitive to oil degradation; oil changes every 12,000–15,000 km are critical. Intake carbon buildup is minimal due to lack of EGR in petrol variants, though direct injection can lead to minor injector deposits over time. The engine's simplicity makes it highly serviceable and durable when maintained properly.
Oil Specs: Requires BMW Longlife-01 (5W-30) specification (BMW SIB 11 01 19). ACEA A3/B4 compliance required.
Emissions: All B42 S20 A units meet Euro 6a (VCA Type Approval #VCA/EMS/8812). No Euro 6c variant exists.
Power Ratings: Measured under SAE J1349 standards. Output consistent across fuel qualities meeting EN 228 (BMW TIS Doc. A27060).
BMW Technical Information System (TIS): Docs A27060, A27155, A27205, SIB 11 01 19
VCA Type Approval Database (VCA/EMS/8812)
SAE International: J1349 Engine Power Certification Standards
The BMW B42 S20 A was used exclusively in MINI's F56 platform with transverse mounting. It replaced the older N13B20 in the Cooper S (pre-facelift) and was later superseded by the B48TU. This engine received specific calibration tuning for MINI's sportier character and uses a unique intake manifold design. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the right-side cylinder block, near the exhaust manifold (BMW TIS A27260). The 7th VIN digit indicates engine family ('S' for B-series petrol). Visual identification: red valve cover with MINI branding, no turbocharger, and a naturally aspirated intake manifold. Critical differentiation from B48: B42 S20 A is naturally aspirated; B48 units feature a turbocharger and larger intercooler. Service parts are not interchangeable with turbocharged variants due to ECU, intake, and fuel system differences (BMW TIS A27060).
The B42 S20 A is one of BMW's most reliable modern engines, with minimal inherent design flaws. Internal MINI quality reports from 2021 indicate very low failure rates across 100,000+ units monitored. UK DVSA MOT data shows fewer emissions-related failures than turbocharged counterparts. However, deferred servicing and use of incorrect oil can accelerate wear on the Valvetronic system and timing components. Regular maintenance ensures longevity beyond 150,000 km.
Analysis derived from BMW technical bulletins (2015–2020) and UK DVSA failure statistics (2018–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW B42S20A.
Comprehensive technical documentation and regulatory references
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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