ACL Bearing Company is aware of the RB30 main bearings 7M2394H being used in RB26 prior to the RB26 mains 7M2428H being introduced and we believe these have functioned quite satisfactorily, however
the differences between the two sets are:
1) the RB26 upper mains have 5 oil holes and the RB30 has only 1 (engine builders were drilling the additional holes)
2) the RB26 plain mains are 20 mm wide vs 19mm for RB30- The 19mm wide bearings have been functioning quite satisfactorily as the ACL 7M2428H was introduced with 19 mm wide mains, however since having a number of requests for the 20 mm wide bearings, we will be making a running change to the 7M2428H set, which should be available approx late December 05. (the additional 1mm is an equal 0.5mm per side)
3) the Flanged main for the RB26 is .002" (0.050 mm) wider than the RB30 main, so endfloat will be slightly different if RB30 mains were used (this may still be within acceptable limits)
The ACL RACE bearings premiumTrimetal bearingsand are specifically designed for high performance engines. The material used is a high strength copper lead material bonded to a steel backing, with an improved strength overlay, for added fatigue strength. Con rod bearings have a hardened steel backing material which helps maintain their crush under higher load and temperature conditions during operation.
Design features-
Bearing eccentricity- (i.e the reduction in wall thickness from the thickest section at the crown of the bearing to the point 10mm from the parting line) is increased to compensate for bore distortion which will occurr due to higher inertia loads, and to assist with formation of the oil wedge to build thevital hyrdrodynamic oil film which seperates the shaft and bearing, to prevent wear. This also helps to maintain a good oil flow through the bearings, essential for heat dissipation away from the bearings.
Crush-is the amount the shells are circumferentially longer than the true half diameter of the housing bore. Crush is increased on these bearings for improved bearing retention and heat disipation.
Wall size tolerance is +/- 0.004 mm (+/- 0.00015") for consistent vertical oil clearances.
The trimetal bearing is a high load carring bearing, with good surface properties(i.e seizure resistance, dirt embedability, conformability) with enhanced chemistry of the overlay plated surface layer for improved fatigue resistance. Fatigue resistance is also improved on the con rod bearings by reducing the overlay thickness to 0.013mm (0.0005"), and there is no flash plating on the bearing backs, so there is no "migration" of plate on the bearing backs under heavy loading, improving thermal transfer and seating of the bearings in their housings.
These bearings are available in 7M2428H -STD/0.025 / 0.25/0.50
7M 2428HX-STD (this gives 0.025 mm(0.001") extra clearance over the 7M2428H-STD)
6B2960H-STD/0.025/0.25
6B2960HX-STD
RB 25 uses the same main bearings as the RB30 7M2394H/HX
Same con rod bearings as the RB26 6B2960H/HX
It is acceptable to use bearings of adjacent size together on the one journal to get the required vertical oil clearances eg a .025 shell with a STD shell
Product Engineering ACL Bearing Company
