M5x

The BMW M5x range of engines are a line of 6-cylinder engines, fitted to BMW models between 1991 and 2001. The range is comprised of two main units; the M50 and the M52. All M5x engines are fundamentally based on the M20 engine that powered the E30 320i, 323i and 325i, and are therefore very popular engine swaps.

Versions

M50

The M50 engine first saw action under the bonnet of the E34 ad E36 as the humble 2.0 variant before being enlarged to 2.5 in 1993. Being little more than an M20 engine with a 24V head, these engines are great upgrades for those who have tired of the M20 donk. Considering there is no difference when installing, there is little or no point fitting the weaker 2.0 version of the M50.

M50 engines weigh 138kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M50B20	2.0 L (1990 cc/121 in³)	110 kW (150 hp) @ 6000	190 N·m (140 ft·lbf) @ 4700	6750	80mm	66mm	1991
M50B25	2.5 L (2494 cc/152 in³)	141 kW (192 hp) @ 6000	245 N·m (181 ft·lbf) @ 4700	6500	84mm	75mm	1991

M50TU

After letting the M50 prove itself, BMW released a Technical Update for the engine in 1993, announcing the new engine as the M50TU. These units featured an even more complex head design incorporating VANOS technology; a variable-valve timing system that modifies the position of the intake camshaft. This has no effect on the overall power of the engine, but does improve torque at lower revs.

Because of this increased complexity, VANOS engines are best avoided for first-time engine swappers.

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M50TUB20	2.0 L (1990 cc/121 in³)	110 kW (150 hp) @ 5900	190 N·m (140 ft·lbf) @ 4700	6750	80mm	66mm	1993
M50TUB25	2.5 L (2494 cc/152 in³)	141 kW (192 hp) @ 5900	250 N·m (184 ft·lbf) @ 4200	6500	84mm	75mm	1993

M52

Despite being heavily based on the M50, the M52 was a whole new engine, and it feels it. 20kg slimmer and a lot more responsive at the pedal, these engines are the most desirable of the M5x swaps.

M52 engines weigh 118kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M52B20	2.0 L (1990 cc/121 in³)	110 kW (148 hp) @ 5900	190 N·m (140 ft·lbf) @ 4700	6500	80mm	66mm	1994
M52B25	2.5 L (2494 cc/152 in³)	123 kW (170 hp) @ 5500	245 N·m (181 ft·lbf) @ 3950	6500	84mm	75mm	1995
M52B28	2.8 L (2793 cc/170 in³)	142 kW (193 hp) @ 5300	280 N·m (207 ft·lbf) @ 3950	6500	84mm	84mm	1995

M52TU

Another Technical Update came in 1998, affecting all the M52 engines with a system called Double-VANOS, which applied the existing VANOS technology to the exhaust camshaft as well. Alongside that, the Block of the engine was changed from cast iron to aluminium, and the engine management system was upgraded. Unfortunately, all this complexity somehow robbed the M52 of its charm, and these Double-VANOS units are best avoided.

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
M52TUB20	2.0 L (1990 cc/121 in³)	110 kW (148 hp) @ 5900	190 N·m (140 ft·lbf) @ 3500	6500	80mm	66mm	1998
M52TUB25	2.5 L (2494 cc/152 in³)	123 kW (170 hp) @ 5500	245 N·m (181 ft·lbf) @ 3500	6500	84mm	75mm	1998
M52TUB28	2.8 L (2793 cc/170 in³)	142 kW (193 hp) @ 5500	280 N·m (207 ft·lbf) @ 3500	6500	84mm	84mm	1998

Components

Sump

E34 Sump with baffle plate

Just like any other engine, the sump is an oil bath to soak the bottom end of the engine, and to capture all the precious Oil that filters back down from the top of the engine.

The sump is one of the most important aspects when fitting an M5x engine to your E30, since its size will have an impact on which engine mounts you use and how the engine is positioned on top of the crossmember. The E34 sump will have the main body at the front of the engine, while the E36 sump is at the back. It is imperative that you fit the E34 sump.

While all sumps are interchangeable, there are some subtle differences between them. The M50B20 sump fitted to the E34 have a blanking plate where the oil level sensor should be; this can be unscrewed and a standard M50 oil sensor put in.

To fit the E34 sump to an M52 engine, you will need to remove the internal baffle plate (see pic). The plate unbolts, but it is also necessary to drill or grind down the mounting columns so that the bottom of the dish is flat.

Oil Pump

The M50 and M52 pumps are both fitted at the front of the engine, and are both driven from a chain drive from the crankshaft (visible when the sump is removed.

Block

The block is one of the most contentious elements when it comes to M5x engines. While internal structure of M50 and M52 blocks are different in a large number of ways, they are similar enough to allow the internal components to be interchangeable.

The real issue is the construction material. While the M50 engines relied on cast iron to provide a steady heat source and a solid body, the M52 engines were built from aluminium to decrease weight.

Unfortunately, aluminium's malleability make it unsuitable for cylinders, and therefore the cylinder bores were coated with a second metal to protect against bore wear. The disastrous choice of material would become a byword for modern BMW engines, and is something that still haunts the company's reputation today. That material was Nikasil.

The Bavarian boffins had looked at the effect of sulphur on Nikasil, and were aware of the damaging affects. For that purpose, they fitted all US engines with cast iron blocks, but pumped out the Nikasil version to the rest of the world. Unfortunately for BMW, British suppliers started buying American fuel, which was far richer in sulphur than the Ultra-Low Sulphur petrol available in mainland Europe at the time. Within just a few years, M52 engines were suffering from catastrophic engine wear, causing huge financial and technical headaches for BMW, and a dark cloud was to hang over engines tainted with the Nikasil reputation.

Years later, it's not easy to find a Nikasil block; most were converted to steel liners or scrapped. But the M52 reputation was already tarred. While some owners reported "moving liners" causing engine damage, others found hot-running engines not only buckled their heads but also stripped the threads from the blocks, ruining the engine beyond repair. In this way, the M52 developed a perhaps undeserved reputation for unreliability, which is why the M50 iron block is preferred despite its extra weight.

Anyone considering a turbo conversion on their M5x engine is advised to stay well away from the M52 block.

Crankshaft

M50 main bearing caps should be torqued to 20Nm, and then a torque angle of 50 degrees.

Piston Rods

Piston rods, or con rods, connect the pistons to the crank. At the top or 'small end', the piston is held in place with a gudgeon pin, while at the bottom or 'big end', rod caps bolt around the cap.

The rod lengths for M5x engines are as follows:

• M50B25 - 135 mm (non VANOS engine)
• M50B25TU - 140 mm
• M52B25 - 135 mm
• M52B28 - 135 mm

Piston Head

M50 and M52 pistons are

Head

Just like the blocks, the Heads fitted to M5x engines are fundamentally the same lumps of metal; so similar that they all share the same head gasket.

However, there are some crucial differences that stop these being completely mix-and-match components.

The M50 head is a twin-cam unit based around an 'interference' design with valves that protrude into the cylinder, resulting in a higher compression ratio than the M52.

The valve timing between the two heads also varies slightly.

The Non-Vanos head uses double valve springs as standard

Inlet Cam

The M50 inlet cam lobes are 1mm than the M52.

Valves

M50 valve stems are thicker.

VANOS

Main article: VANOS

Head Gasket

The biggest indication of how similar the two heads are is the identical head gasket.

Intake

The main difference between the 325 and 328 inlet is the plastic manifold and the size of the ports in it. This manifold is 10mm greater (width) in port size over the standard 328. The 325 has 55x25mm port's and the 328 has 45x25mm port size.

Wiring

Loom

Main article: M5x Looms

The M5x series of engines differ substantially from their M20 predecessors in the labyrinth of wires that wind their way around the engine bay. Fortunately, BMW designed them to be detachable, and therefore the primary engine loom is a one-piece component terminating in a plug called the X20. This plug is the counterpart of the C101 plug on the M20 loom, although the pin layout differs substantially.

You will therefore need to adapt the M5x loom to mate up to the existing E30 wiring. You can either buy a ready-made loom (we recommend DanThe) or use our loom tables to make your own.

ECU

M50 engines come with a red label 413 ECU or a silver label 413 ECU. The silver labeled ECU uses EWS

EWS

Main article: EWS

EWS is the immobiliser system fitted to BMW models with M50 and M52 engines from 1994 onwards. Its basic function was to check that the doors were unlocked correctly and that the correctly-coded ignition key is being used. If it fails to detect the right signal, it will disable the ignition circuit, the injectors and the starter motor, which is a right pain if you're trying to do an M50 or M52 engine swap.

If you are trying to chip-tune your M5x engine, you will need to disable the EWS to do so. Learn more about disabling the EWS.

Ancilliaries

Engine Mounts

Because of the differences in height of the M50 and M52 engines compared to E30 engines, there is a choice of engine mounts available.

Engines taken from the E34 have their engine mounts bolted to the front of the engine block. To fit these blocks in an E30 you need to bolt E36 alloy arms to previously unused holes near the middle of the block.

From there, it is recommended to use the rubber engine mounts from the E28 M5.

Exhaust

One of the key features of the M5x engine swap is the exhaust. The standard systems fitted to the donor vehicles are not compatible with the E30, and therefore other solutions must be found to ensure that the exhaust not only does its job properly, but also fits around the steering rack and under the car.

The two options are a custom-made exhaust system using your own manifold and tubing, or to buy a completed kit. There are a number of suppliers of M5x-to-E30 exhaust systems, which we have outlined below:

Off-the-shelf Solutions

Supplier	Offer	Price (£)	Contact
DanThe	Full manifold and front pipes		Contact here
Fritz' Bits	Full 6 branch manifold and exhaust system 2x2.5" system with a X-over pipe Lifetime warranty	1200 inc. VAT	http://www.fritzsbits.co.uk/exhausts.htm

Custom Solutions

Manifold	Method	Result	Exhaust	Method
Standard cast E36 rear manifold cast E36 front manifold	On the front manifold, remove a section between where the three primaries meet the flange, and weld back together		E36 Front pipes 325i E30 system	By chopping up the front pipes of an E36 system and a 325 E30 system and welding the bits together, you can connect to the standard 325 E30 system just in front of the gearbox exhaust mount

Drivetrain

Once you've fitted your engine, you'll want that power to be hitting the back wheels as efficiently as possible. With that in mind, you'll need to select the best combination for you from these three components; the Flywheel, the Gearbox and the propshaft.

Flywheel

Standard and Lightened M20 flywheels

A variety of flywheels can be used, but this entirely depends on which gearbox you are planning to use. The main choice available is the Dual-mass flywheel that comes fitted with the M5x engines, the M20 flywheel which will need some material removing from its face, or the M42 flywheel.

Despite the work involved, most experienced swappers recommend the use of the M20 flywheel. The existing dual-mass wheel is not only extremely heavy but also problematic, and ties you to a gearbox with worse-performing ratios than its M20 counterparts.

Starter Motor

Despite being mounted to the gearbox, the starter motor is intrinsically paired with the Flywheel due to the differences in teeth pitch around the edge of the wheel. This means that an M20 starter must be used with the M20 flywheel, even if an M50 gearbox has been fitted.

The wiring for the starter motor is easily changed over, with the thick and thin red wires simply bolting up to their relevant posts no matter which starter motor you choose to use.

Gearbox

By far the simplest gearbox to fit to your M5x conversion is that fitted to the 318is. This M42-specific gearbox will bolt straight up to the engine and remove the need for any Drivetrain modification such as different differentials. It is also capable of accepting the E36 clutch and flywheel if required, although it is recommended to fit the M20 flywheel.

To operate the gearbox, gear linkages from the M20 gearbox should be used, and it is recommended to fit the Z3 short shifter complete with bearing.

If you wish to use a more modern gearbox, such as that fitted to the M52, then it should be mounted using an M20 gearbox crossmember, and will need the appropriate propshaft to mate up to the differential.

Two types of gearboxes were fitted to the E36. 328's were given a bigger unit (ZF S5D), while 325's and 323's got the smaller (and lighter) Getrag S5D. Both are fine for any M50 engine, but still necessitate a change away from the E30 propshaft.

The best gearbox to use is from an H plate 520i or 525i 24v. These early 24v cars used a Getrag 260 overdrive gearbox which is identical to an E30 325i and E34 525i unit, but the bellhousing bolt pattern is altered to make the engine sit over at more of an angle. This means you can use the existing 325i prop and not have to fit a different final drive

Clutch

The clutch has to match the gearbox you are using. No matter whether it's M5x, M20 or M42, the preferred brand of clutch is Sachs.

Propshaft

Depending on which gearbox you use, you will be forced to use a certain propshaft to make use of your new engine.

If you have fitted the M42 or M20 gearbox, then a standard E30 propshaft can be used.

If you have fitted a more modern M50 or M52 gearbox, then you have one of two choices. Try to buy a used E30 M3 propshaft, or make your own using E36 components. By using the front and rear halves of an E36 325 prop with an E30 centre bearing, you should be able to mate up your new gearbox to your rear diff with the appropriate propshaft length.

Combinations

Engine	Flywheel	Clutch	Gearbox	Propshaft	Modifications
M52B28	M20 325i	M20 325i	M20 325i	M20 325i	Modified E30 325 gearbox crossmember using E30/E36 gearbox mounting rubbers E30 325 gear shift rods which need to be twisted slightly
M52B28	M20 325i	M20 325i	M42 318iS	M20 325i	E30 318iS gearbox crossmember using E30/E36 gearbox mounting rubbers E30 320 gear shift rods Ff using the M42 box a new M20 spigot bearing is needed (12mm hole)
M52B28	M20 325i	M20 325i	E36 328i	E36 328i	Propshaft should be fitted with a reversed E30 centre bearing Note the E36 box is a 1:1 final drive so a low ratio diff will be required (e.g. 2.93:1, 3.25:1)
M52B28			M40	E30 318/320	The props mentioned have a longer front section

Brakes

While the 24v conversion doesn't deliver much more raw power, it does make the E30 a lot more sprightly when it comes to accelerating. It is therefore crucial to make sure your brakes are up to scratch.

Because of the bulk of these engines, there is little room for a brake servo of the size usually fitted to the E30. Therefore the servo fitted to a Renault Clio (2000 or later) can be used with very little modification.

If you are considering a dramatic overhaul of the braking system, learn more about brake upgrades.

Throttle Cable

If converting to M50, then a standard E36 throttle cable should fit to the E30 pedal perfectly.

Servicing

Main article: Basic M5x Servicing

Common Problems

Not Turning Over

This is a common problem for those engines fitted with the M20 flywheel. The lip of the flywheel will either be catching on the block where the long rear sump bolts come home, or the bolts that hold the flywheel onto the crank will be too long.

The solution to this is either to grind away a small section of the sump (not recommended), or have the flywheel lightened by removing part of the lip. Either way, the engine and gearbox will have to come out of the engine to cure the problem.

Not Starting

If NOTHING happens when you turn the key, then you have an issue with the red wire that feeds the ignition switch from the fuse box.

If nothing engine-related happens when you turn the key, then the issue is with the plain green wires that drive the ignition. These wires are found behind the glovebox, where you will probably find a pair not connected to anything; these need to be joined together.

In the same area as these green wires, you should find two single plug and sockets, each joining a black/yellow wire to another wire (plain black, usually). Disconnect both of these and plug the two halves with black/yellow wires together.

This bypasses the auto inhibitor switch, and arranges the wiring just as it would be from the factory on a manual car. Follow the two left over wires to a relay, remove the relay base, the wires, and the other wires to the relay, which you will find a lead to the area under the front console where your gear lever will be. You need to find the reverse light loom and gear lever grommet from a manual E30, which will connect between the reverse light switch on the gearbox and the plug you have found.

Overheating

The aluminium blocks used in the M52 are a lot more sensitive to overheating than the cast-iron M50. For this reason, serious overheating has been known to completely kill an M52 engine beyond economical repair.

VANOS Chatter

A problem with the sprocket on early VANOS engines caused a problem with chattering. Although it doesn't highlight any mechanical failings or loss of performance, the noise can be downright annoying.

In 1995 BMW released an updated sprocket designed to deal with this problem.

See also

• Engines
• M20