FAQ

What does HX mean?

The ‘X’ signifies the set will give .001” (0.025mm) extra oil clearance on a Std shaft.

When are HX bearings used?

When additional oil clearance is required (usually for high performance applications) and for select fitting to obtain the required clearance.

Can I mix and match bearings of different sizes?

It is common practise to adjust oil clearances by mixing bearings of adjacent grades, ie H-STD and HX-STD. The maximum difference between shells should be no more than .0005”/.013mm. The thicker wall size bearing should be fitted in the most heavily loaded position.

Why do RACE Series bearings have variable colouring?

The final operation in the manufacture of ACL RACE Series engine bearings is electroplating. In this operation the bearing appearance changes to a dark tarnished colour which can vary from black / brown / blue / copper. This colouration is restricted to the surface atoms and has no effect on bearing performance.

What is the recommenced oil clearance for Race series?

ACL Race series bearings can be assembled with .00075” - .001” per 1” of journal dia. (0.020-0.025mm per 25 mm of journal dia.) plus 0.0005” (0.013 mm). This is a good starting point, with actual oil clearance determined by the engine builder depending on application.

Does the notch on a bearing prevent it from spinning in operation?

No, the notch is purely there for location/orientation. Many OEM bearing designs have deleted notches. The bearing crush ensures the bearings are held tightly in the housing.

Why do some main bearing sets contain formed single-piece thrust bearings while others have assembled 3-piece self-aligning thrust bearings?

Single piece thrust bearings have strong self-supporting characteristics that allow secure fitment and good float control. Self-aligning thrust bearings adapt to ensure optimum alignment and maximum heat transfer. ACL select the type of bearing based both on the OEM specification and on design optimisation for performance applications.

Why do some engines have 2 (upper and lower) thrust bearings when others only have 1?

OEM engine designers have decided the thrust area on one flange is adequate to take the engine thrust load. Some Race series sets have 2 (upper & lower) thrust bearings (when OEM design is only 1 shell) to allow for heavier thrust load from heavier duty clutch etc.

What does the “D” mean in some bearing part numbers?

Part numbers that contain a “D” denote the set will suit conrods fitted with dowel pins for bearing location. It is usually only the lower bearing shells that have a dowel hole.

What are recommended thrust (bearing) clearances (end float)?

Up to 70mm journal: 0.10 – 0.15 mm (.004” - .006”)

70 - 90mm journal: 0.15 – 0.20 mm (.006” - .008”)

Over 90mm journal: 0.20 – 0.25mm (.008” - .010”)

Why do some main sets have thrust bearings with oversize thrust thickness on higher undersizes? (Same applies to separate thrust washers).

Increasing the thickness of both the bearing shell (undersize) and the thrust thickness (oversize) allows for simultaneous reconditioning of both the crankshaft journal and the thrust faces.