TL;DR
This guide covers the swap we’re doing: an OBD1 European E36 316i (M43B16) to an M50B25 non-VANOS. Our car is a January 1994 sedan.
The short version, from owners who have done the four-cylinder-to-M50 swap: it’s essentially an engine replacement with a few extra parts. Collect every part before you start. The M50 engine harness plugs into the same chassis connector as the four-cylinder harness. The extra work is in cooling, mounts, exhaust, driveshaft and, on cars that have it, the immobiliser.
Part numbers: look them up by VIN on RealOEM for the six-cylinder donor model. They vary with year and body style.
Decisions to make first
Why the M50 non-VANOS?
- Simpler: no VANOS unit to maintain or reseal.
- Matches the car: our 1994 316i is OBD1, and so is the M50. Bentley lists the non-VANOS M50 with Bosch DME M3.1 (1992 engines) and the VANOS M50 with DME M3.3.1 (1993–95). Use the DME and harness that belong to the donor engine.
- The trade-off: the non-VANOS engine was only built up to August 1992, so donors are older and rarer than the VANOS M50TU. See the M50 vs M50TU vs M52 comparison.
Does the car have EWS?
Bentley: the first E36 immobiliser (EWS) was introduced in January 1994. It’s a module under the left side of the dashboard that interrupts ignition, fuel injection and the starter, armed by the central locking. The coded-key EWS II followed in January 1995.
A January 1994 car sits right at the changeover, so check whether yours has the module before buying a DME. Owners who put an M50 into an EWS-equipped four-cylinder E36 report that it needs wiring work at the EWS module and a suitable DME. See the EWS guide.
Gearbox
The M20, M40, M42, M43, M50 and M52 share the same gearbox bolt pattern, so the four-cylinder car’s gearbox physically bolts to the M50. Owners report the four-cylinder Getrag gearbox works behind an M50, but its type decides the driveshaft (see below). See the gearbox selection guide for whether it can take the extra torque.
Buy the most complete donor you can
An engine that comes with its harness, DME, alternator, A/C compressor, power steering pump, exhaust manifolds, intake boot and air flow sensor saves the most time and guesswork.
Parts list by system
Engine and ancillaries (ideally with the donor)
- M50B25 long block with its intake and exhaust manifolds, throttle body and fuel rail
- alternator, power steering pump, A/C compressor (if you want A/C)
- DME and the complete engine harness from the same donor: don’t modify the M43 harness
- air flow sensor and intake boot
- all engine sensors (crank, cam where fitted, coolant and air temperature, oxygen sensor)
Cooling: from a six-cylinder E36
- six-cylinder radiator with its hoses. Bentley shows the four-cylinder radiator with an integral expansion tank; the six-cylinder uses a separate tank.
- six-cylinder fan shroud and expansion tank (the shroud carries the tank), plus the long hose from engine to tank and the short one from tank to radiator
- driver’s-side lower radiator mount: owners report the four-cylinder one is too wide for the six-cylinder radiator
- six-cylinder auxiliary fan (it mounts on the bumper side)
- new water pump, thermostat, cap and clamps: see the cooling system overhaul
Mounts and chassis
- six-cylinder engine mount arms
- engine mounts: four-cylinder mounts are reported to sit a little taller but work if healthy; if buying new, buy six-cylinder ones
- six-cylinder front anti-roll bar: the four-cylinder bar doesn’t dip low enough to clear the M50’s oil pan
- the four-cylinder transmission crossmember is reported to fit, using a different set of holes in the body
Driveline
- driveshaft: the four-cylinder rear section is reported to fit, but the front section is too long. You need a front section for a Getrag gearbox; a ZF front section won’t bolt to the flex disc.
- six-cylinder shift linkage
- clutch and flywheel: the four-cylinder parts can survive, but a six-cylinder flywheel and clutch is the reliable choice. The six-cylinder clutch needs the six-cylinder flywheel.
- new flex disc and centre bearing while the shaft is out
Exhaust
- a complete six-cylinder exhaust: none of the four-cylinder exhaust bolts to the M50 manifolds. Keep the small hangers on the bracket behind the driveshaft centre bearing.
Intake, fuel, controls
- six-cylinder airbox
- throttle cable: the four-cylinder one is reported to work but is slightly too long
- power steering lines from the M50 pump, ideally
- vacuum lines: map the donor’s vacuum routing before taking it apart
Gaskets and service items before installation
While the engine is on the stand: valve cover, oil pan and oil filter housing gaskets, plus every seal you can reach. Fit a new rear main seal while the gearbox is off.
Optional
- Differential: a shorter final drive (owners mention the 3.15 used with the six-cylinder) changes the character; a four-cylinder ratio works.
Registration in Slovakia
In Slovakia an engine change has to be approved and registered with the vehicle inspection authority. Check the current requirements and the documents they want for the donor engine before you start the swap.
Recommended order
- Check for EWS and decide on the DME and gearbox.
- Source the donor complete, and photograph every connector, bracket and hose before it comes apart.
- Remove the M43, labelling every connection on the car side.
- Reseal and service the M50 on the stand, including the full cooling system.
- Fit the six-cylinder mount arms, anti-roll bar and radiator mount.
- Install the engine and gearbox; fit the driveshaft with a new flex disc and centre bearing.
- Fit the exhaust, then the wiring, cooling, fuel and intake.
- Fill and bleed everything, check for leaks with the ignition on, then make the first start.
Where to look up and buy parts
| Site | Use |
|---|---|
| RealOEM | Part numbers and diagrams by VIN |
| Autodoc | Common service parts, delivers to Slovakia |
| Schmiedmann | BMW specialist, used and new |
| FCP Euro, ECS Tuning | Wide BMW range, ship to the EU |
This guide is the cornerstone of the Projekt 36 swap series. We’re installing an M50B25 NV into a 1994 E36 316i sedan in Košice, Slovakia. Every step will be documented with photos as we go.
→ Related: M50 vs M50TU vs M52 Comparison | Cooling System Overhaul | Swap Wiring Differences
