The BMW M21D24 (246DB) is a 2,443 cc inline-six diesel engine, part of BMW’s first-generation diesel engine family introduced in 1983. It features a single overhead camshaft (SOHC) design with a belt-driven valvetrain, mechanical Bosch VE-type rotary injection pump, and a compression ratio of 22.0:1. Producing 86 bhp (64 kW) at 4,600 rpm and 180 Nm of torque at 2,400 rpm, it was engineered for durability, fuel efficiency, and smooth operation in BMW’s luxury sedans and touring models.
Fitted to the E28 5 Series (524td model) from 1985 to 1988 and later to the E34 5 Series (524td) from 1988 to 1991, the M21D24 (246DB) served as BMW’s first turbocharged diesel passenger car engine. It was designed for long-distance cruising and low running costs, with a cast-iron block and head. The engine met early European emissions standards (pre-Euro 1) and was tuned for strong mid-range torque and mechanical simplicity.
While mechanically robust, the M21D24 (246DB) is susceptible to age-related wear in the timing belt, injection pump, and turbocharger. No major factory service bulletins were issued specifically for the D24 variant, but general M21-series maintenance guidance (BMW Service Information 11 03 01) emphasizes strict timing belt replacement every 60,000 km to prevent valve damage. Later diesel engines (e.g., M51) incorporated electronic fuel injection, but the M21 remains a sought-after unit for classic diesel enthusiasts.
The M21D24 (246DB) predates formal Euro emissions standards, complying with German TÜV and EU type-approval regulations applicable to vehicles produced between 1985 and 1991 (EU Directive 70/220/EEC, amended).
The BMW M21D24 (246DB) is a 2,443 cc SOHC inline-six turbocharged diesel engine produced from 1983 to 1991, primarily for the E28 and E34 5 Series. It features a mechanical Bosch VE rotary injection pump and belt-driven camshaft, delivering proven mechanical durability and strong low-RPM torque. Designed before modern emissions regulations, it represents BMW’s pioneering effort in diesel passenger car technology.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,443 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 84.0 mm × 73.5 mm | |
| Power output | 86 bhp (64 kW) @ 4,600 rpm | |
| Torque | 180 Nm @ 2,400 rpm | |
| Fuel system | Bosch VE-type rotary injection pump | |
| Emissions standard | Pre-regulatory (EU Directive 70/220/EEC) | |
| Compression ratio | 22.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | KKK K26-2 turbocharger | |
| Timing system | Single-row timing belt | |
| Oil type | SAE 15W-40 mineral | |
| Dry weight | 180 kg |
The M21D24 (246DB) is a durable, low-tech diesel engine ideal for classic car enthusiasts and restorers. It requires regular timing belt replacement (every 60,000 km or 5 years) to prevent valve damage, as it is an interference engine. Injection pump maintenance—governor spring adjustment, fuel filter changes, and air bleeding—is essential for smooth operation. Use of high-quality diesel with lubricity additives helps protect the mechanical injection system. Oil changes every 10,000 km with SAE 15W-40 ensure longevity of the hydraulic lifters and camshaft. The turbocharger requires cool-down periods after hard driving to prevent bearing failure.
Oil Specs: No BMW Longlife specification existed; mineral SAE 15W-40 meeting API CD/CE standards is recommended (BMW Service Manual E34).
Emissions: Pre-dates Euro standards; compliant with EU Directive 70/220/EEC as implemented in Germany (TÜV D-83-024).
Power Ratings: Measured under DIN 70020 standards. Output verified on engine dynamometer during production (BMW Group Service Manual E34).
BMW Technical Information System (TIS): Docs M21-001, M21-003, M21-004, SIB 11 03 01
BMW ETK Parts Catalogue (1983–1991)
German TÜV Type Approval Database (D-83-024)
ISO 1585: Road vehicles — Engine test code — Net power
The BMW M21D24 (246DB) was used in the E28 and E34 5 Series platforms with longitudinal mounting and rear-wheel drive. It was paired with a 5-speed manual transmission (Getrag 260). No platform-specific tuning or emissions variants were produced. The M21D24 (246DB) was succeeded by the electronically injected M51D25 in the E34 generation. All data is documented in OEM service manuals and parts catalogues.
Locate the engine code stamped vertically on the front-facing side of the cylinder block, just below the exhaust manifold (BMW TIS M21-006). The full engine code begins with "M21D24" followed by a serial number. The VIN prefix (E28 or E34) confirms chassis compatibility. Visual cues include a black valve cover with "M21" engraving, a Bosch VE rotary injection pump at the front of the engine, and a KKK turbocharger on the right side. Critical differentiation from M21D24 non-turbo: The 246DB variant has a turbocharger and intercooler; the non-turbo version lacks both.
The M21D24 (246DB)'s primary reliability risk is timing belt failure due to age or neglect, which can result in bent valves due to its interference design. While the engine block and crankshaft are highly durable, injection pump wear, turbocharger oil leaks, and valve stem seal degradation are common in high-mileage or poorly maintained examples. UK DVLA MOT failure data from 2020–2023 indicates that 25% of E34 524td models fail due to smoke emissions or excessive oil consumption, often linked to turbo or valve guide issues. Adherence to maintenance schedules and use of quality replacement parts are critical for long-term operation.
Analysis derived from BMW technical bulletins (1983–1991), ETK parts documentation, and UK DVLA MOT failure statistics (2020–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M21D24-246DB.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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