Tri-metal crankshaft main bearings ACL King BMW N54B30 N55B30 S55B30

The BMW N54B30, N55B30 and S55B30 six-cylinder engines

The N54B30, N55B30 and S55B30 are BMW's 3.0-litre turbocharged inline six-cylinder engines (2,979 cc, bore 84 mm, stroke 89.6 mm). The twin-turbo N54B30 was built from 2006 to 2016, the single-turbo N55B30 from 2010 to 2019, and the S55B30, the twin-turbo engine of BMW M (M2 Competition, M2 CS, M3, M4), from 2014 to 2020. ACL and King offer a single main bearing set for these engines; the King bearings are reserved for the N54B30 and N55B30.

The crankshaft of these engines runs on seven main bearings. The journal of main bearing 1 (Ø 64.96 mm) is larger than those of main bearings 2 to 7 (Ø 55.96 mm), so the running clearance is given for each of the two diameters. Each journal turns between two half shells, one seated in the block and the other in the main bearing cap: they carry the crankshaft. The ACL Race Series and KING RACING tri-metal sets shown here replace them on built engines.

Tri-metal main bearings

A tri-metal 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 14 half shells, seven pairs for seven main bearings.

An aluminium bi-metal takes around 8,000 psi, a performance tri-metal 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 main 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 tri-metal 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 GPC range trimetal bearings for very high loads: a silver-based overlay containing solid lubricant particles, topped with a polymer coating that protects the bearing in case of oil starvation and 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	Trimetal: steel back, bronze layer, silver-based surface
Alloy	Race Series (copper-lead)	GPC (silver-based overlay)
Protective coating	No	Yes, polymer coating
Available sizes	Standard to +0.50 mm (+ increased clearance HX)	Standard to +0.25 mm (+ increased clearance STDX)

Vehicle compatibility

This main bearing set fits the BMW N54B30, N55B30 and S55B30 six-cylinder engines (King bearings: N54B30 and N55B30 only):