BMW M50B25 engine

The largest German manufacturer BMW AG is famous for its premium class cars. Reliable and durable engines of this brand are characterized by a very wide range and will please any sophisticated owner. Starting from the turbo 3-cylinder B38, 4-cylinder M10-M40 and N20/B48, 6-row M20/M50 and N54/N55 to the first-class V8 M60-N63 and V12 models for the leading series. Powertrains designed for the city and more sporty versions are produced, along with gasoline produced diesel, atmospheric and turbocharged. Everyone can buy a car based on the preferred modification, version and configuration of the motor.  In Russia and the CIS, Bavarian BMW models are also not neglected.

M50B25 engine specifications

Advantages

For this modification of the engine was developed a new mechanics of the cylinder head, consisting of 24 valves, two DOHC camshafts, lightened intake manifold thanks to plastic, introduced gas distribution mechanism VANOS and hydrocompensators. Optimized “torque” and “idle speed”, “noise of the unit”, reduced consumption of gasoline and the coefficient of “toxicity”.

Technically changed ignition mechanism, it became fully electronic, added to each plug individually ignition coil, installed an updated idle speed regulator, air flow sensor made of thermal film, timing drive was replaced by a chain with a long service life. The CMM mechanism has been modified, due to the installation of more durable and lightweight pistons and connecting rods, the value of the radius of valve stems has been reduced and their acceleration indicators have been changed. The connecting rod length for the M50B25 engine was 135 mm, and for the M50B25TU 140 mm.

The motor is famous for the fact that, despite the short period of release, it is still popular and on its basis were developed a series of three-liter power units with a capacity of 240-250 horsepower, as well as it became the basis for the release of internal combustion engine brand S50 sports car models. The interval of acceleration to 100 kilometers per hour BMW 5 series 525i E34 was 8.6 seconds, less than in the series 520i E34 with 2 – liter engine M50B20 in 10.6 seconds.

Disadvantages

A list of major difficulties:

1. Overheating. In order to avoid overheating of the internal combustion engine, it is necessary to prevent the radiator and timely replacement of the fan thermo clutch. Changing the coolant and flushing the mechanism consistently every two years will help to avoid overheating of the engine due to the large number of moving parts of the motor. Air plugs in the cooling system can cause overheating hazards.
2. Trolling, no spark. Trolling is usually caused by malfunctioning plugs, injectors and ignition coils and is usually solved by replacing them.
3. Floating revolutions, noises in the cylinder head. If there are initial signs of insufficient engine traction, it is necessary to inspect the structural units. The source may be the engine decompression mechanism and air suction, ignition coil breakdown. Diagnostics of ignition coils every 100000 km, will prevent the problem of floating revolutions. And in case of damage to the oil rings, they just need to be replaced. Also to eliminate the issue of “floating revs” you need to check the serviceability of the flow meter and Vanos device. The increase in vibration when the working temperature of the unit is set at idle causes strong jolts and prevents the continuous delivery of fuel. This is due to the individuality of the Vanos mechanism and is considered a factory defect that was eliminated later. The solution may be the purchase of its repair kit.
4. Oil Leakage. Timely inspection and replacement of the alternator housing gasket or crankshaft oil seal will prevent such a problem as “engine oil leakage”. If you use analogs of crankshaft oil seals, they should be replaced more often than original consumables.
5. Excessive oil consumption. The issue of excessive engine oil consumption is solved by replacing the oil caps and all components of the oil pipeline every 100000 km, otherwise you may encounter a breach of tightness of the main oil pipe connections and complete wear of the oil caps.
   It is better to immediately put new original oil-resistant rings, as they are of higher quality and will last longer than analogs.
6. Increased fuel consumption. Fuel consumption increases due to the collapse of the catalytic converters. Getting the honeycomb of collapsed catalysts into the cylinders will be the consequence of all sorts of scratches. The first signs will be the scuffing of the piston, it begins to curve and hit the top point. With scuffing you can drive of course, but not for a long time, because you will have to buy a new motor, as the price of repair will be high. Passing maintenance at the dealer, with the extension of the warranty, treatment with composition against wear and scoring NT-10 after timely diagnostics by AGC method will help to avoid it.

The owner of a BMW car, who wants to replace his engine with a 2.5 – liter M50 B25, may have confusion in the choice, namely, what is better to choose, with or without the Vanos system.

If we rely on the reviews of car owners who have such experience, we can conclude that the M50B25 is more simple, reliable and inexpensive. And M50B25 TU is more tractive, the design of the motor is better because of the longer connecting rods of 140 mm, they are longer by 5 cm, and a lightweight piston, it has an improved control mechanism, has two detonation sensors, but it is more capricious and difficult to repair. In addition, the price of repair will be more expensive.

For proper installation of the Vanos system you need special equipment for fixing camshafts, the qualification of an experienced motorist will further depend on the oil and fuel consumption of your engine, whether there will be problems with lack of spark and traction.

Technical specifications

The M50B25 is an atmospheric gasoline inline 6-cylinder engine with 24 valves, water-cooled and distributed injection of gasoline DME Motronic 3.1 by Bosch, in the intake manifold, DOHC. The aluminum intake and exhaust ports of the cylinder head are distributed opposite each other. The cast iron cylinder block consists of molded cylinders, cooling jacket, crankcase top and 7 crankshaft supports.

The highest output of this 2.5-liter engine with a volume of 2494 cubic centimeters is 192 horsepower / 141 KWT at 5900 rpm. With a torque of 245 Nm and from 4700 rpm, the cylinder cross section is 84 mm and the piston stroke is 75 mm. The piston group under compression ratio is equal to 10 and includes 7 pieces of main bearings, there is no supercharger. The combustion chamber has a working volume of 41.57 cubic centimeters with a value of 77 horsepower per 1000 cubic centimeters.

The factory M50B25 TU motor is a 24-valve, water-cooled, inline 6-cylinder gasoline engine with Motronic 3.3.1 distributed gasoline injection from Bosch in the intake manifold, DOHC.  To improve the environmental friendliness of the engine and within the framework of fuel economy, and most importantly to increase acceleration was installed Vanos system. Updated pistons and connecting rods have been installed, and changes have been made to the valves and crankshaft.

The greatest performance of this 2.5 – liter power unit with a volume of 2494 cubic centimeters, has 192 horsepower / 141 KVT at 5900 rpm. With a torque of 245 Nm and from 4200 rpm, the cylinder cross section is 84 mm and the piston stroke is 75 mm. Piston group under compression ratio is equal to 10.5 and includes 7 pieces of main bearings, there is no supercharger. The combustion chamber has a working volume of 41.57 cubic centimeters with a value of 77 horsepower per 1000 cubic centimeters. There is no supercharger.

The engine M50B25 TU was mounted on BMW fifth series cars

Movement of the cooling emulsion is made with the help of a water-tight pump driven by the crankshaft and toothed chain belt of the timing device. To control the temperature of the technical cooling fluid when the engine is not warmed up and to maintain a comfortable operating temperature, a thermostat is installed in the cooling mechanism. This thermostat of the engine cooling system opens at a temperature of 80-92 degrees and a pressure of 1.5 to 2 bar.
To diagnose the exhaust gas device, the idling speed of the M50V25 unit for the step gearbox is 650-700 rpm. To maintain acceptable fuel and air composition and to measure exhaust gas composition, an oxygen sensor with progressive signal change is installed. The ignition module, spark plugs and wires form a microprocessor-based ignition mechanism, which is not further adjusted or serviced.

The injector engine, with rear-wheel drive and 5-speed manual, is controlled by the electronic system Motronic 3.1 by Bosch. Based on lambda probe data, it calculates the opening time of the injection valves, favorable for fuel and air matching, which is certainly not calculated when adjusting manually. In the upper part of the timing mechanism there are two camshafts, just above the cylinder block, which increases the power of the unit, evenly distributes the load, reduces gasoline consumption and engine noise.  With the help of installed hydraulic compensators, engine noise is reduced, valves do not need adjustment. It is recommended to replace the timing chain belt every 250000 kilometers.
Stable idling speed is achieved by the throttle valve with the help of automatic control and correction of data on the advance of the ignition mechanism.

The throttle sensor, which regulates the throttle at idle, is coordinated by the idle solenoid valve. In the event of a failure, adjustment or replacement should only be carried out by the manufacturer’s service center.

BMW manufacturer recommends AI-95 gasoline for use. Original synthetic motor oil 5w-30, 5w-40 to 10w-40 and 15w-40 depending on the time of year, brake fluid DOT 4 and original from the manufacturer of coolant or antifreeze based on ethylene-glycol, will support flawless operation of the engine.

The average consumption of gasoline per 100 kilometers is from 6.8 to 11.5 liters, engine oil with filter 1 liter, coolant 5 liters and brake fluid 1.2 liters. It is recommended to change the engine oil every 7000 -10000 kilometers, and change the disposable filter at least once a year, but at the same time as the oil change. With a constant cycle with full oil filtration, engine lubrication is carried out by a combined type and controlled by a baroscope. In case of increased engine operation, the engine oil and filter are changed according to the indications of technical inspection. Brake fluid should be changed after one year and antifreeze every two years. Depending on the type of transmission, the manufacturer’s recommendation for use of oil for mechanics is SAE 75W-90, for automatic transmission G 052.
The power unit with proper care can increase its resource of more than 400000 kilometers.

The designers of the M50B25 power unit put in the markings of the following indicators: M – indicates the series family of the unit, the category of row and the number of cylinders – means the number 5, and 0 – notifies about the lack of changes in the basic version, well and the letter B indicates the type of fuel – gasoline and location within the family, in this case it means longitudinally or transversely, the number 25 speaks of the volume in liters, in this case it is 2.5 liters.

The installation of the motor is designed on the front of the car next to the front suspension longitudinally.  Vin code of the engine can be seen in the upper part of the block near the fourth cylinder.

The M50B25 motor is installed on BMW third and fifth series cars, such as 325i E36 and BMW 525i E34 series, as it was produced for only five years.

Tuning and increasing power.

Every car owner would like to get extra power from the engine and feel instant results. At the same time, he believes that there will be no consequences from this. It is worth noting that the manufacturer does not install chip tuning because of the need to comply with strict parameters of the ecology of exhaust gases.
Depending on the budget component, you can consider four main options, performing tuning yourself or turning to a specialist.

• Stroker build.
  By installing on the M50B25 TU crankshaft with stroke parameters of 84mm and making firmware SIEMENS MS41, the output can be increased to 2.8 liters and power up to 220 horsepower.
  You can get 230 horsepower by installing components from the M54B30 engine. Namely, the stroker is a long-stroke crankshaft, other parts that are part of the Cinder Block, main liners and injectors.
• Schrick 264*256 camshafts can be used to get the M50 B25 3.0 unit up to 260 horsepower.
  The 280 horsepower can be obtained by properly tuning the ECU and installing Schrick 284*284 camshafts, straight-through exhaust system, equal length exhaust manifold, S50 injectors, and 6-throttle intake.
• Get 500 horsepower with a Garret GT 35 turbo kit and a set of CVTs with an 8.5 compression ratio and 550 SS injectors.
• You can install the chip with firmware from the Bavarian company AC Schnitzer by yourself or contact a specialist. The manufacturer promises to increase maximum speed, power and torque, as well as reduce fuel consumption by changing the coefficients. These indicators the owner of the modernized engine should feel after 100 km of mileage, but provided that the motor has not previously had problems, and it worked without failures, otherwise you may encounter low compression and floating revolutions on “cold”. And it will be necessary to deal with the idle speed sensor.

It happens that the owner of the car has to replace the engine due to the loss of its quality characteristics. And in this case, he can take advantage of two Swap options.  The first is replacement with a unit of the same series. The second option is replacement with an engine with improved power indicators, but of a different series. True in this case it will be necessary to replace the transmission and additional mountings.

When carrying out this procedure, it is worth considering that in connection with the increase in the characteristics of the power of the internal combustion engine, the load on other parts of the car increases, for example, the transmission and wheel supports. Therefore, it is worthwhile to make and replace them with the appropriate models.

In addition, the power unit Swap must be registered with the traffic police to avoid problems with law enforcement officers during inspection, or with customs when crossing the border.

In order to maintain its safety in the future, the procedure of replacing the motor should be carried out only by proven specialists in workshops.
It should also be borne in mind that the price of installing a Swap engine will be quite high due to the cost of the power unit itself, spare parts and services of a specialist.

Despite the fact that the M50B25 series engine was produced for only 5 years, it is still in demand among BMW owners. It is appreciated for its stable operation, long service life and unpretentiousness in maintenance.

This engine is installed on the following models:

BMW 3-Series (E36)

BMW 5-Series (E34)