BMW 520i (E34) engine: which one, problems and replacement

The BMW 520i in the third 5 Series generation (E34, built 1988–1996) was built with 3 different engines over its life: the M20B20 (129 hp, 1977–1992), the M50B20 (150 hp, 1990–1996) and the M50TUB20 (150 hp, 1992–1995).

Below you will find how to identify the engine in your 520i, the faults to look for, current prices for a replacement and the swap options that make sense.

• Generation: third 5 Series, 1988–1996
• Body styles: E34 (saloon, Touring)
• Engines: M20B20, M50B20, M50TUB20
• Output: 129 hp and 150 hp
• Replacement engines in stock: 7 from 907,00 €

Which engine is in your 520i?

M20B20 in the 520i

The M20B20 was used in the E34 520i, built 1977–1992. It is a 2.0 L naturally aspirated petrol inline-6 with 129 hp and 164 Nm. Compared with the M50B20 (150 hp) and M50TUB20 (150 hp), it is the mildest.

Reading the code: M marks an M-series code, the naming BMW used for its engine families up to the early 2000s; 20 is the family number; B stands for petrol (from the German Benzin); 20 is the capacity in decilitres, so 2.0 litres.

M50B20 in the 520i

The M50B20 was used in the E34 520i, built 1990–1996. It is a 2.0 L naturally aspirated petrol inline-6 with 150 hp and 190 Nm. Compared with the M20B20 (129 hp) and M50TUB20 (150 hp), it is in between.

Reading the code: M marks an M-series code, the naming BMW used for its engine families up to the early 2000s; 50 is the family number; B stands for petrol (from the German Benzin); 20 is the capacity in decilitres, so 2.0 litres.

M50TUB20 in the 520i

The M50TUB20 was used in the E34 520i, built 1992–1995. It is a 2.0 L naturally aspirated petrol inline-6 with 150 hp and 190 Nm. Compared with the M20B20 (129 hp) and M50B20 (150 hp), it is in between.

520i engines by model year

The engine changed 4 times during the E34 run, in 1990, 1992, 1993 and 1996. Changes usually come with BMW's mid-life update (LCI) or a new emissions standard, so a car registered early in a year can still have the older engine. The VIN settles it.

Other cars with the same engine as the 520i

A replacement engine does not have to come from another 520i. These models left the factory with the same engine code, so a unit from any of them is a candidate donor once the sump, mounts and ancillaries are matched to your car.

M20B20: BMW E30 320i, BMW E28 520i.

M50B20: BMW E36 320i.

M50TUB20: BMW E36 320i.

How to confirm your engine code

Because the 520i used more than one engine, the badge alone does not tell you which one your car has. The build date is the first clue; the VIN is the proof. Send us the last seven characters of the VIN and we read the engine code from BMW's records, or look for the code stamped on the block. How to find your BMW engine code.

Known 520i engine problems

M20B20 (M20 family)

The M20B20 in the 520i shares the known weak points of the M20 family. Full M20 guide.

Timing belt failure. The M20 is an interference engine. If the belt or tensioner fails, pistons hit valves and the head is scrap. Belts should be changed every 60,000 km or four years, whichever comes first.

Cylinder head cracks. Heads crack between the camshaft journals or between valve seats after overheating. Coolant loss and a sweet smell are the clues.

Rocker arm and shaft wear. Rocker arms can crack and the retaining clips can walk off the shaft. The 'rocker arm fix' with improved clips is a known upgrade.

Oil spray bar and cam wear. A loose or blocked spray bar starves the cam lobes. The result is a worn cam and noisy valve train.

Water pump and thermostat. The water pump is driven by the timing belt and is normally changed with it. A weeping pump can soak the new belt.

M50B20 and M50TUB20 (M50 family)

The M50B20 and M50TUB20 in the 520i share the known weak points of the M50 family. Full M50 guide.

Cooling system. Plastic water pump impellers, thermostat housings and expansion tanks crack, and overheating can warp the head.

VANOS seals (M50TU). The VANOS piston seals harden and the engine loses low-down torque and idles roughly.

Crankcase ventilation valve. The CCV valve can freeze or clog, pressurising the crankcase and pushing oil past seals.

Oil filter housing gasket. The gasket hardens and leaks oil down the side of the block.

Valve cover gasket. A common leak that also lets oil into the spark plug wells.

Symptoms to watch for on the 520i

Rattle for a few seconds after a cold start. The classic sign of a weak timing chain tensioner or stretched chain. It must be checked quickly: a chain that jumps a tooth can bend valves.

Poor low-down torque and uneven idle. VANOS seals or solenoids. The engine may run well at high revs but feel flat and lumpy at low speed.

Engine stops suddenly and will not restart. On belt-driven engines, a snapped timing belt. Do not keep cranking: on an interference engine the valves are probably already bent.

Looking after the 520i engine

M20 engines

• Oil: 10W-40 or 15W-40 semi-synthetic, about 4.25 litres with filter.
• Service interval: Oil every 7,500 km; valve clearances every 15,000 km; belt on time, not only on distance.
• Timing drive: Rubber timing belt with tensioner, changed with the water pump every 60,000 km or four years.
• Workshop notes: Valve clearance is set cold at about 0.25 mm with eccentric adjusters. Use a new head bolt set whenever the head comes off.

M50 engines

• Oil: 5W-40 or 10W-40 synthetic, about 6.5 litres with filter.
• Service interval: Oil every 10,000 to 15,000 km; cooling system as a set every 100,000 km.
• Timing drive: Duplex lower chain and single upper chain at the front with hydraulic tensioner.
• Workshop notes: Hydraulic lifters, no valve adjustment. Refresh VANOS seals when fitting a used M50TU.

Buying a used engine for the 520i: checklist

1. Warranty terms in writing. Read what the warranty covers, how long it runs and what fitting conditions apply. Most warranties require a qualified workshop, new fluids and filters, and replacement of the cooling parts that caused the original failure.
2. Photographs from every side. Good suppliers photograph the actual engine you will receive. Look for the block stamp, the sump, the timing cover and any broken brackets or connectors in the pictures.
3. Gearbox and flywheel match. Manual and automatic engines differ at the flywheel or flexplate, and sometimes at the crankshaft spigot. Make sure the engine you buy matches your gearbox or that you transfer the right parts.
4. List of what is fitted. Engines are sold with different ancillaries: some have the turbo, injectors, manifolds, alternator and starter, others are long blocks. Agree the list in writing so you know which parts must come from your old engine.
5. Compression or leak-down figures. Even compression across all cylinders tells you more than mileage. Ask for the figures, not just a pass or fail, and compare the highest and lowest readings: a spread above 10 to 15 percent deserves a question.
6. Timing chain noise. Listen for a rattle at the front of the engine for the first seconds after a cold start. On an engine that cannot be run, look at the chain guides through the oil filler or with the valve cover off.
7. Timing belt history. A timing belt must be changed on time and distance. With no dated record, treat the belt, tensioner and water pump as due and replace them before the first start.
8. VANOS operation. Rough idle, a rattle from the front of the head and a loss of torque at low revs point to VANOS seals or solenoids. These are serviceable parts and are easier to renew with the engine out.
9. Originality and numbers. For collectible cars, the engine number and correct ancillaries add value. Photograph the stamp and keep it with the car's documents.
10. Plastic cooling parts. Expansion tanks, thermostat housings and water pump impellers made of plastic crack with age. Plan to replace them when the engine is fitted.

BMW 520i replacement engine cost

Across 7 520i engine units in our stock today, prices start at 907,00 € and reach 3.133,00 €. The median — the price in the middle of the range — is 1.313,00 €.

Prices depend on the exact version, the donor's mileage, how complete the engine is and the demand for that code. Higher-output versions, low mileage and dressed engines with turbo, injectors and ancillaries cost more; long blocks and higher mileage cost less.

2 of these come from E34 donor cars, priced from 928,00 € to 1.485,00 €. An engine from the same body is the most direct swap because the sump, mounts and ancillaries already match.

On top of the engine, budget for the workshop's labour and the parts that are best replaced while the engine is out: engine mounts, the rear main seal, cooling parts, a clutch or converter seal, fluids and filters.

Replacement engines in stock for the 520i

Here is a selection of 520i engines currently on our shelves, photographed in the yard. Click any of them for the full photographs, mileage and specification.

BMW M50TUB20 Engine907,00 €BMW E36 320i M50B20 Engine, Premium Grade3.133,00 €BMW E34 520i M50TUB20 Complete Engine928,00 €BMW E34 520i M50B20 Complete Engine1.485,00 €BMW E36 320i M50TUB20 Complete Engine937,00 €BMW M50B20 Engine1.313,00 €

BMW M50TUB20 Engine — 907,00 €, reduced from 1.500,00 €. It comes from a recorded donor car, and 8 units are available. The listing shows every side of the engine and the fitted parts.

BMW E36 320i M50B20 Engine, Premium Grade — 3.133,00 €, reduced from 3.600,00 €. It comes from a recorded donor car, and 27 units are available. The listing shows every side of the engine and the fitted parts.

BMW E34 520i M50TUB20 Complete Engine — 928,00 €, reduced from 1.500,00 €. It comes from a recorded donor car, and 17 units are available. The listing shows every side of the engine and the fitted parts.

BMW E34 520i M50B20 Complete Engine — 1.485,00 €, reduced from 2.000,00 €. It comes from a recorded donor car, and 27 units are available. The listing shows every side of the engine and the fitted parts.

BMW E36 320i M50TUB20 Complete Engine — 937,00 €, reduced from 1.500,00 €. It comes from a recorded donor car, and 21 units are available. Ask the desk for compression figures or extra photographs before you order.

BMW M50B20 Engine — 1.313,00 €, reduced from 1.700,00 €. It comes from a recorded donor car, and 14 units are available. We can confirm fitment against your VIN the same day.

Will it fit my 520i?

Will the M20B20 fit my BMW E34 520i?

The M20B20 is the original engine for the BMW E34 520i, which makes it the straightforward choice. The third 5 Series was built 1988–1996, and the M20B20 was produced 1977–1992, so check that your car's build date falls inside that window. Confirm the drive type (rear-drive or xDrive), the gearbox (manual or automatic) and the emissions standard, because these can change the sump, the flywheel and the software. Send us the VIN and we check all of it for you.

How much is a replacement engine for a BMW E34 520i?

We do not have an M20B20 on the shelf for the E34 520i at the moment. Units arrive regularly; send us your VIN and we will tell you when the next one is ready and what it will cost, including delivery.

Will the M50TUB20 fit my BMW E34 520i?

For the BMW E34 520i, the M50TUB20 is the factory engine and the one to order. The third 5 Series was built 1988–1996, and the M50TUB20 was produced 1992–1995, so check that your car's build date falls inside that window. Confirm the drive type (rear-drive or xDrive), the gearbox (manual or automatic) and the emissions standard, because these can change the sump, the flywheel and the software. Send us the VIN and we check all of it for you.

How much is a replacement engine for a BMW E34 520i?

We have 1 M50TUB20 engine from E34 donor cars, priced from 928,00 €. Delivery to your door is included, and the engine carries a 12-month warranty when fitted by a qualified workshop. Add fitting labour and the parts you replace at the same time — seals, cooling parts and mounts — to estimate the total.

Engine swaps and upgrades for the 520i

These engines were fitted to other versions of the E34 at the factory, which makes them the most practical upgrades: the body was designed around them and many parts are shared.

Can I fit the M20B25 in my 520i?

Yes, it is one of the more common upgrades. Both are petrol inline-6 engines, so the mounting points are similar, but the M20B25 needs its own wiring and engine control unit, the matching gearbox or clutch, and often a different sump, cooling and exhaust. The gain is 20 hp and 36 Nm. In Germany and most of Europe an engine swap must be inspected and registered.

Can I fit the M50B25 in my 520i?

Yes, it is one of the more common upgrades. Both are petrol inline-6 engines, so the mounting points are similar, but the M50B25 needs its own wiring and engine control unit, the matching gearbox or clutch, and often a different sump, cooling and exhaust. The gain is 42 hp and 55 Nm. In Germany and most of Europe an engine swap must be inspected and registered.

Can I fit the M50TUB25 in my 520i?

Yes, it is one of the more common upgrades. Both are petrol inline-6 engines, so the mounting points are similar, but the M50TUB25 needs its own wiring and engine control unit, the matching gearbox or clutch, and often a different sump, cooling and exhaust. The gain is 42 hp and 55 Nm. In Germany and most of Europe an engine swap must be inspected and registered.

Fitting a replacement engine in the 520i

1. Inspect or replace the timing chain parts. Look at the guides and tensioner. On high-mileage engines, replacing them now costs far less than doing it later.
2. Fit a new timing belt kit. Fit a new belt, tensioner and water pump and set the timing with the correct tools before the first start.
3. Reset VANOS adaptations. Clear the VANOS adaptations so the ECU learns the camshaft positions of the new engine.
4. Fill with the right oil and prime it. Fill with new oil of the correct specification and a new filter. Crank with the fuel and ignition disabled until oil pressure builds.
5. Coding and adaptations. On modern BMWs, the engine ECU must be matched to the car's immobiliser (CAS, FEM or BDC). Reset adaptations, register the battery and clear faults with diagnostic software.
6. First start and leak check. Start the engine, let it idle and watch oil pressure, temperature and fault codes. Check for leaks and bleed the cooling system.
7. First 1,000 km. Drive gently for the first few hundred kilometres, vary the engine speed and avoid full load. Change the oil and filter after about 1,000 km to remove any assembly debris.

The full fitting and first-start procedure.

Delivery, warranty and payment

Before a 520i engine leaves our Hamburg yard it is drained of oil and coolant, every opening is sealed, and it is strapped to a pallet and wrapped. We send photographs of the packed unit and the tracking details.

Door-to-door delivery is included to the address you give at checkout. Typical delivery takes three to five working days within Germany and neighbouring countries and five to ten working days to the rest of Europe and the UK.

Every engine carries a 12-month warranty on eligible internal failure when a qualified workshop fits it with new fluids and filters. Payment is by card, bank transfer or crypto; your invoice is emailed as soon as you order.

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