BMW M54 and S54 Engines (2000-06)

The BMW M54 and S54 were inline six-cylinder petrol engines for BMW’s standard and ‘M’ models, respectively. Available from 2000, the M54 replaced the M52 engine.

The M54 and S54 engines both had an aluminium block with cast iron cylinder liners, an aluminium cylinder head, double overhead camshafts (DOHC), variable intake and exhaust camshaft timing (double VANOS) and four valves per cylinder.

Compared to the M52TU engine, the M54 engine had:

• New pistons with shorter skirts (though a graphite coating continued to be used to reduce friction);
• A modified intake with shorter ram tubes and an increased diameter;
• An electronically-controlled throttle valve (EDK) for intake air control; and,
• Siemens MS 43.0 engine management system which provided multiple spark ignition up to 1350rpm (varying with engine temperature) and up to 20 degrees after TDC (top dead centre) to
  1. provide clean burning during engine start-up and while idling, and,
  2. to keep the spark plugs clean for longer service life.

For the M54 engine, the intake manifold was split into two groups of three runners to increase low-end torque. The intake manifold also had separate (internal) turbulence bores which channeled air from the idle speed actuator directly to one intake valve of each cylinder. Routing the intake air to only one intake valve caused the intake to swirl in the cylinder. Combined with the high flow rate of the intake air (due to the small cross sections), this reduced fluctuations and provided more stable combustion.

In the intake manifold, a resonance flap was controlled by the engine management system. At low- to mid-range engine speeds, the resonance flap was closed to produce a long/single intake tube for velocity, which increased engine torque. Furthermore, as a cylinder’s intake valve closed, incoming air would stop and expand back (i.e. resonance wave back pulse), and then enter the next cylinder in the combustion cycle. From around 4100 rpm (depending on temperature), however, the resonance flap was open, allowing the intake air to pull through both resonance tubes, providing the air volume necessary for additional power.

S54B32 engine

The S54B32 engine was used in BMW’s E46 M3,E36/7 Z3 M Roadster and E36/8 Z3 M Coupe. The S54B32 was an evolution of the S50B32 engine – itself based on the M50 engine – and differed from the M54 engines in that it had a high-strength cast iron block, a forged steel crankshaft which underwent ‘nitro-carburised’ heat treatment and six individual throttle assemblies with electronic throttle control.

Compared to its S50B32 predecessor, the S54B32 engine had:

• An 87.0 mm cylinder bore (increased from 86.4 mm) for a capacity of 3246 cc (previously 3201 cc);
• High-pressure double VANOS, a first for six-cylinder BMW Motorsport engines;
• An 11.5:1 compression ratio (previously 11.3:1);
• Siemens MSS 54 engine management system;
• Finger-type rocker arms for reduced reciprocating mass and friction;
• A one-piece cast aluminium cylinder head; and,
• A ‘scavenging’ oil pump to maintain oil pressure during heavy cornering.

S54B32HP

The S54B32HP engine was reserved for the E46 M3 CSL. Compared to the S54B32, the S54B32HP engine had:

• A high-flow carbon fibre air intake;
• Modified valve and camshaft timing;
• Retuned DME using a MAP sensor (rather than a MAF sensor);
• A lightweight exhaust manifold (subsequently introduced for other M3 vehicles);
• Thinner exhaust piping; and,
• Slightly straightened intake and exhaust manifolds.

BMW M54 engine problems

M54 double VANOS failure

For the M54 engine, the VANOS units may fail due to deterioration of the VANOS piston seal O-rings which are made from Buna (a material with limited temperature resistance). Over time, the O-rings harden and shrink, causing them to lose their functional characteristics – this can cause symptoms such as a loss of power below 3000 rpm, surging around 3000 rpm, a louder idle and rough running, and rough running.

The piston O-rings lies under and provides support to a Teflon piston seal ring. Replacing the O-rings requires the Teflon seals to be removed for access. Since the Teflon seals cannot be removed from the piston seal groove without damaging it, the Teflon and O-ring seals must be replaced simultaneously. For greater longevity, the Buna O-rings can be replaced with O-rings made from Viton.

The VANOS unit had two piston seals with O-rings, while each piston had two O-ring sizes to provide hydraulic sealing in two VANOS cylinders of different sizes and an additional, smaller O-ring that was used to seal off a piston bearing. It is understood that the O-ring for this cap was also made from Buna and deteriorated in the same manner as the piston seal O-rings.

M54 double VANOS rattle

VANOS rattle generally occurs from 1800 to 2200 rpm, but may also occur at idle. The rattle is caused by wear in the variable valve timing helical (slanted) gears which are found on the camshaft, camshaft sprocket and splined shaft which attaches to the VANOS unit. Wear of the helical gear allows the camshaft to have lash movements that engage the splined shaft axially; the axial play that causes the rattle is found on the helical gears and the splined shaft bearing.

Removing the splined shaft bearing axial play significantly reduces the VANOS rattle. The splined shaft bearing is made of a thick washer and two thrust (roller) bearings. The washer and two thrust bearings are encased in a ring and two outer flat washers; the complete bearing is housed inside a splined shaft cavity that is closed with a threaded cover.

Since the thrust bearings and centre washer have tight tolerances, they cannot be replaced. To fix, a replacement VANOS piston bearing ring is manufactured to the same specification as the original bearing ring but with a shorter height (manufactured to a tight height tolerance). The bearing ring is a difficult and expensive component to manufacture since it is made from a special bearing steel, hardened and its surfaces ground. For further information, see http://www.beisansystems.com/procedures/double_vanos_rattle_procedure.htm.

BMW S54 engine problems

S54 connecting rod bearing wear

In the S54 engines, the connecting rod bearings can wear prematurely and, ultimately, fail – this occurs because of insufficient rod bearing clearance which, in turn, results in inadequate oil lubrication between the crank journal and the rod bearing. For a discussion of this problem, please see http://www.m3post.com/forums/showthread.php?t=887379.

S54 VANOS failure

For the S54 engine, the VANOS unit has an oil pump disc with two holes and the exhaust hub has two driver tabs that insert into the oil pump disc holes. Due to excessive rotational pressure force or rattling/hitting force, one or both of the driver tabs can break – if this occurs, VANOS malfunction and engine fault codes will be issued. A broken tab can stay lodged in the VANOS oil pump disc hole or it can drop to the oil pan. In rare cases, the tab can engage the chain and sprockets, causing engine damage.

S54 VANOS solenoid failure

The VANOS solenoid coil pack may fail due to cracked solder joints which are the connector pins on the PCB (printed circuit board).

S54 VANOS rattle

Apparent at idle or engine speeds from 1800 to 2200 rpm, the VANOS rattle is caused by

• Wear in the variable valve timing helical (slanted) gears which are found on the camshaft sprocket and splined shaft; and,
• Loose intake sprocket mounting bolts.

For the former (the focus of this section), wear of the helical gear allows the camshaft to have lash movements that engage the splined shaft axially. The axial play that causes the rattle is found on the helical gears and the splined shaft bearing.

As with the M54 engine, the thrust bearings and centre washer have tight tolerances and cannot be replaced. To fix, however, the piston bearing ring can be replaced with a ring that is made of bearing steel that has been hardened and ground to bearing standards – its height can be controlled to provide a tight axial bearing fit. Furthermore, outer flat washers can be combined to provide the necessary height for a tight fit.

A diaphragm spring incorporated in the intake and exhaust sprockets also affected VANOS rattle since this spring loads the sprocket rotational movement to dampen quick movements. Since the spring weakens over time, replacing it with a new one is often needed to completely fix the rattle.