Trimetal connecting rod bearings BMW N54B30 N55B30 S55B30

The BMW N54B30 N55B30 S55B30 six-cylinder engines

The N54B30 is BMW's 3.0-litre twin-turbo direct-injection inline six (2,979 cc, 84 mm bore, 89.6 mm stroke), built from 2006 to 2016. The N55B30 succeeded it from 2009 with a single twin-scroll turbocharger, and the S55B30 is the M division's twin-turbo version fitted to the M2, M3 and M4. All three engines share the same crankpin diameter: a single bearing set covers the family, from 299 to 500 hp depending on the version.

From the factory, BMW fits this engine with connecting rod bearings graded by colour class (part numbers 11 24 7 576 714 yellow, 11 24 7 576 715 violet, 11 24 7 628 034 red and 11 24 7 628 035 blue), 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. On the King side, the complete set is made up of 3 CR222GPC boxes of 2 pairs.

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. Its Calico version (HC suffix) adds the CT-1 coating, a dry film lubricant that reduces friction and abrasive wear.
	King Engine Bearings, an Israeli manufacturer of high-performance engine bearings since the 1960s, offers with its GPC range a silver-based tri-metal: steel back, lead-bronze intermediate layer and a silver-based overlay containing solid lubricant particles. Its 10-micron polymer coating protects the bearing in case of oil starvation or metal-to-metal contact.

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	Tri-metal: steel back, lead bronze, silver-based overlay
Alloy	Race Series (copper-lead)	GPC (silver, solid lubricant)
Protective coating	No (Race); Calico CT-1 (HC)	Yes: 10 µm polymer
Available sizes	Standard to +0.50 mm (+ increased clearance HX)	Standard to +0.25 mm (+ increased clearance STDX)

Vehicle compatibility

This connecting rod bearing set fits the BMW N54B30, N55B30 and S55B30 six-cylinder engines: