The BMW M52 inline 6-cylinder engine was used in a variety of BMW models, including the E36 3 Series, the E39 5 Series Sedan, the Z3 and the E46 3 Series.

The M52 was an upgrade to the successful M50 engine. The M52 was produced in 2.0 (M52B20), 2.5 liter (M52B25) and 2.8 liter (M52B28) configurations. When the BMW E46 3 Series was launched in 1999, the M52TU engine was introduced in the E46 323i, E46 328i and the E39 528i models. The major changes in this Technical Update were the redesigned crankcase, modified pistons, Double VANOS for the camshaft drive, and Siemens MS42 DME system. Later, the E39 523i was introduced with the M52B25TU engine.

BMW took a large step in 1994 with the introduction of an aluminum block with the wear-resistant Nikasil coating on the cylinder bores. This reduced the engine's weight from around 190 kg (M50) to some 160 kg (M52). The camshafts were now fitted with counterbalancing masses, as was already the case on those of the eight-cylinder engine.

With the introduction of the M52 a new BMW power-output characteristic was introduced as well. The maximum power of 192 bhp previously achieved with the 2.5-liter engine was now reached with a 2.8 liter engine that delivered a significantly higher maximum torque. The new 2.5-liter engine was positioned between the 2.0-liter and 2.8-liter versions with its 170 bhp.

As a special version for four countries with high-sulfur gasoline, the M52 was supplied with a cast-iron cylinder block. The Nikasil cylinder coating would have had marginal reliability under those operating conditions.

In 1998 the VANOS system, which initially adjusted only the inlet camshaft was developed into the Double-VANOS system which now adjusted the timing of the exhaust camshaft as well. This opened the potential for further optimization of the engine's performance.

Double-VANOS system

The inlet system was provided with two technical refinements in 1998. One was a flap valve in the inlet plenum chamber that cut off the inlet passages of the front three cylinders from the rear three. The differentiated intake system, known as DISA, optimized the engine's running under full load. The other refinement was a dedicated system of tubes of very small diameters through which the inlet air was drawn during idling or when running at low loads. The increased turbulence that this achieved improved the combustion process and thus reduced exhaust emissions.

In order to be able to offer a single cylinder block to all markets throughout the world, the aluminum block was given dry cast-iron liners.

source: Geschichte des Motors, Dr. Karlheinz Lange