Trimetal connecting rod bearings BMW M3 E46 Z3 M Z4 M S54B32

The BMW S54B32 six-cylinder engine

The last naturally aspirated inline six from BMW's M division, the S54B32 powers the BMW M3 E46 from 2000 and then the Z3 M and Z4 M: a 3,246 cc engine with an 87 mm bore and a 91 mm stroke, twin overhead camshafts and 24 valves, producing 320 to 360 hp depending on the version (M3 CSL). It was built until 2008.

From the factory, BMW fits this engine with connecting rod bearings graded by colour class, blue (part numbers 11 24 7 835 440 and 452) and red (11 24 7 835 439 and 451), selected according to the machining tolerances of the crankpin. These are standard production bearings, sized for the loads of the original engine: as soon as power, engine speed or boost pressure increase, they reach their limits.

Trimetal connecting rod bearings

A trimetal bearing stacks three layers: a steel back, a copper-lead intermediate layer with high load capacity and an anti-friction running surface that protects the journal. The complete set contains 12 half shells, six pairs for a six-cylinder engine.

The original bearing relies on an aluminium alloy over a steel back, intended for low to medium loads, whereas trimetal is designed for high, sustained loads: an aluminium bi-metal takes around 8,000 psi, a performance trimetal up to 12,000 psi, 50% more. Hence better resistance and better durability on turbocharged, supercharged and high-revving engines.

Technical specifications

Technical guide

The ACL and King rod bearings shown here are trimetal bearings, designed for engine building and racing. Compared with an original bearing, they handle far higher loads: they cope with increased power, high rpm or the addition of a turbo or supercharger, where a standard bearing quickly reaches its limit.

The two brands

	ACL Bearing Company, an Australian manufacturer of high-performance engine bearings since 1949, offers with its Race Series precise trimetal bearings, available in many sizes and proven on built engines worldwide.
	King Engine Bearings, an Israeli manufacturer of high-performance engine bearings since the 1960s, offers with its pMax Black trimetal alloy bearings designed for heavy loads, with a pMaxKote coating available as an option (XPC version).

Construction and advantages

Criterion	ACL Race Series	King Racing
Cross-section
Type	High-performance trimetal bearing	High-performance trimetal bearing
Country of manufacture	Australia	Israel
Construction	Trimetal: steel back, copper layer, soft surface	Trimetal: steel back, copper layer, soft surface
Alloy	Race Series (copper-lead)	pMax Black (hardened copper-lead)
Protective coating	No	pMaxKote (optional, XPC version): polymer coating on the surface that limits wear when lubrication drops (start-ups, thin oil film).
Available sizes	Standard to +0.25 mm (+ increased clearance HX)	Standard to +0.50 mm (+ increased clearance STDX)

Vehicle compatibility

This connecting rod bearing set fits the BMW S54B32 six-cylinder of the M3 E46, Z3 M and Z4 M: