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ACL trimetal connecting rod bearings Porsche 993 M64 3.6 3.8

ACL trimetal connecting rod bearings Porsche 993 M64 3.6 3.8

€97.89 (tax incl.)

€108.77 (tax incl.) -10%

Set of 12 trimetal connecting rod half-bearings for Porsche 911 (993) M64.

Brand and treatment: ACL Race
Compatibility: 911 (993) Carrera 3.6 and 3.8, Carrera RS, Turbo, GT2
Engine codes: M 64.05 to M 64.08, M 64.20 to M 64.24, M 64.60
Available sizes: standard to +0.25 mm, increased-clearance version (HX)

6B2473H-STD

Choice Brand - Coating Anti-Friction :: ACL RACE - Without treatment

Choice Dimension :: STANDARD

32 in stock in Europe (72h lead time)

Available in stock in Europe (72h lead time)

ORDER TODAY, WE SHIP IN 5 - 15 DAYS

The Porsche 993 M64 flat-six engines

The M64 of the Porsche 911 type 993 is the last air-cooled flat-six: 3.6 litres in the Carrera (M 64.05 to M 64.08, M 64.21 to M 64.24) and in the turbocharged Turbo and GT2 (M 64.60, M 64.60R, M 64.60RS), 3.8 litres in the 3.8 Carrera, Carrera 4 and Carrera RS (M 64.05S, M 64.06S, M 64.20, M 64.21S). ACL lists the same bearing set for all these engines: a single set covers the family.

From the factory, this engine is fitted with standard production connecting rod 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

In a trimetal bearing, a steel back carries a copper-lead intermediate layer with high load capacity, itself covered by an anti-friction running layer that spares the crankpin. The set is supplied complete: 12 half shells, i.e. 6 pairs.

Trimetal targets high, sustained loads, whereas aluminium bi-metal is limited to low to medium loads: about 8,000 psi for the latter, up to 12,000 psi for a performance trimetal, 50% more. The benefit shows in strength and durability on turbo, supercharged and high-revving engines.

Technical specifications

Fitment dimensions common to all references

ACL bearings
Crankpin Ø 54.971 / 54.990 mm
Housing bore Ø 58.000 / 58.019 mm
Width 14.8 mm

Reference	Brand and treatment	Size	Wall thickness (mm)
6B2473H-STD	ACL Race - Untreated	Standard	1.499
6B2473HX-STD	ACL Race - Untreated	Std, increased clearance (HX)	1.486
6B2473H-.025	ACL Race - Untreated	+0.025	1.512
6B2473H-.25	ACL Race - Untreated	+0.25	1.624

Running clearance

Running clearance is the gap between the bearing and the crankpin, filled by the oil film.

While the engine turns, the crankpin floats on this oil film, which carries the load without direct contact with the bearing. Film thickness depends on clearance: too tight, oil passes poorly, temperature rises and the risk of seizure grows; too wide, oil escapes, the film carries less and oil pressure decreases. A correct clearance ensures both sufficient lubrication and a well-maintained film.

Size / grade	When to choose it	ACL Race Series
Standard (STD)	Standard journal, not reground	0.057 to 0.068 mm
Increased clearance (HX)	Wider clearance: high oil flow, high rpm	0.082 to 0.093 mm
+0.025 mm	Polished journal	0.057 to 0.068 mm
+0.25 mm	Journal reground to 0.25 mm	0.057 to 0.068 mm

Checking on assembly: lay a calibrated strip (Plastigauge) on the journal, torque the rod cap to spec, then compare the crushed strip against the gauge to read the clearance.

Plastigauge

Order the Plastigauge →

Technical guide

These ACL trimetal connecting rod bearings are aimed at built engines and racing: where a standard bearing quickly reaches its limit, they accept more power, more rpm and more boost. The range includes the standard size, a +0.025 mm size for a crankpin that has only been polished, a +0.25 mm regrind size and the HX version with increased clearance for high-revving engines or engines needing a high oil flow. It allows the same part number to be kept after the crankshaft is reground and the clearance to be tailored to the oil used and the engine's duty.

The brand

An Australian specialist in high-performance engine bearings since 1949, ACL Bearing Company produces the Race Series: precisely made trimetal bearings, available in numerous sizes and recognised on built engines across the world.

Vehicle compatibility

This connecting rod bearing set fits the M64 flat-six engines of the following Porsche 911 (993) models:

Brand	Model (chassis)	Engine code	Power	Years
PORSCHE	911 (993) 3.6 Carrera	M 64.07, M 64.08, M 64.05, M 64.06	272 hp	1993–1995
PORSCHE	911 Convertible (993) 3.6 Carrera	M 64.07, M 64.08, M 64.05, M 64.06	272 hp	1994–1995
PORSCHE	911 (993) 3.6 Carrera 4	M 64.07, M 64.05	272 hp	1994–1995
PORSCHE	911 Convertible (993) 3.6 Carrera 4	M 64.07, M 64.05	272 hp	1994–1995
PORSCHE	911 (993) 3.6 Carrera	M 64.24, M 64.21, M 64.22, M 64.23	286 hp	1995–1997
PORSCHE	911 Convertible (993) 3.6 Carrera	M 64.24, M 64.21, M 64.22, M 64.23	286 hp	1995–1997
PORSCHE	911 Targa (993) 3.6 Carrera	M 64.24, M 64.21, M 64.22, M 64.23	286 hp	1995–1997
PORSCHE	911 (993) 3.6 Carrera 4	M 64.21, M 64.23	286 hp	1995–1997
PORSCHE	911 Convertible (993) 3.6 Carrera 4	M 64.21, M 64.23	286 hp	1995–1997
PORSCHE	911 (993) 3.8 Carrera	M 64.05S, M 64.06S	286 hp	1995–1997
PORSCHE	911 Convertible (993) 3.8 Carrera	M 64.05S, M 64.06S	286 hp	1995–1997
PORSCHE	911 (993) 3.8 Carrera 4	M 64.05S, M 64.06S	286 hp	1995–1997
PORSCHE	911 Convertible (993) 3.8 Carrera 4	M 64.05S, M 64.06S	286 hp	1995–1997
PORSCHE	911 (993) 3.8 Carrera	M 64.21S	301 hp	1995–1997
PORSCHE	911 Convertible (993) 3.8 Carrera	M 64.21S	301 hp	1995–1997
PORSCHE	911 Targa (993) 3.8 Carrera	M 64.21S	301 hp	1996–1997
PORSCHE	911 (993) 3.8 Carrera 4	M 64.21S	300 hp	1995–1997
PORSCHE	911 Convertible (993) 3.8 Carrera 4	M 64.21S	301 hp	1995–1997
PORSCHE	911 (993) 3.8 Carrera RS	M 64.20	300 hp	1995–1997
PORSCHE	911 (993) 3.6 Turbo 4	M 64.60	408 hp	1995–1997
PORSCHE	911 (993) 3.6 Turbo 4	M 64.60	405 hp	1995–1997
PORSCHE	911 (993) 3.6 Turbo GT2	M 64.60R	430 hp	1995–1997
PORSCHE	911 (993) 3.6 Turbo GT2 4	M 64.60R	430 hp	1995–1997
PORSCHE	911 (993) 3.6 Turbo GT2 4	M 64.60RS	450 hp	1997

Why replace the bearings

Replacing the bearings during a build or rebuild guards against the most expensive failure: a worn-out connecting rod bearing scores the crankpin, contaminates the oil circuit with debris and forces at least a crankshaft regrind, or even a new rod and block. Against such costs a new set weighs little: it is the cheapest part of the rotating assembly, but the one whose failure costs the most.