Crankshaft bearing set for the BMW N51, N52, N53, N54, N55, S55
Bearing Design Enhancements
Crush increased for:
Improved bearing retention from higher radial contact pressure. Locks
the bearing into the housing.
More effective heat dissipation through improved thermal transfer.
Bearing Eccentricity
Definition: Gradual reduction in wall thickness between the crown
and parting line.
Race Series performance engine bearings feature increased
eccentricity to improve shape adaptation to compensate
for bore distortion at high speed operation.
Assists in the formation of hydrodynamic oil film
Select Fitting of ACL RACE
Series Bearings
It is common practise to adjust oil clearances by mixing bearings of
adjacent grades i.e. HX-STD with H-STD or H-STD with H- 001 or
H-.025, to obtain desired oil clearance. Using the HX-STD with H- STD
will give .0005” (0.013mm) additional clearance than using two H-STD
shells, and similarly using H-STD and H-001 will reduce clearance
.0005” (0.013mm).
Bearing shells with wall size .0005” (0.013mm) or less can be
assembled on one journal. The thicker wall size bearing is fitted to the
most heavily loaded position i.e. the upper half con rod shell and the
lower half or cap position main bearing.
When using a crankshaft that is to be reground to an undersize, first
measure the assembled bearing ID’s, then have the required journal
sizes ground to match the bearing measurements, with the desired oil
clearance.
Installation of ACL RACE Series
bearings – Oil Clearances
Oil clearances are most accurately measured using micrometres and
bore gauges. Bearing wall thickness measurements are taken at 90
degrees to the parting line (i.e. at the crown of the bearing) using a
micrometre with a ball anvil, for use on the curved ID of the bearing.
Vertical oil clearance is best measured by assembling the bearing in its
housing, with bolts torqued to specification, then using a bore gauge
measure the assembled ID of the bearings at 90 degrees to the parting
faces. The mating crankshaft journal size is measured, and subtracting
this measurement from the bearing ID bore size, gives the assembled
oil clearance.
ACL RACE bearings can be assembled with .00075-.001” per 1” of
journal diameter (0.020-0.025mm per 25mm of journal diameter) plus
.0005” (0.013mm).
As an example for a 2.000” (50mm) journal diameter, 2.000 x .001=
.002 + .0005 = .0025” (50/25 x 0.025= 0.050 + .013 = 0.063 mm)
Bearings should not be polished with abrasive pads or paper, on the
bearing surface, to change the oil clearance.
