Main and connecting rod bearings for the larger heavy-duty frames are split sleeve precision insert type (refer to Figure 300-18). The most common materials are cast iron/babbitt or steel/babbitt. Occasionally, aluminum bearings are used. Aluminum bearings require better oil filtration as they are sensitive to dirt.
Although sleeve bearings are the most common, API 618 allows rolling-element (anti-friction) main bearings for Class A machines up to a rating of 200 HP. Rollingelement bearings are used in some Class B machines for ratings in excess of 1000 HP.
Refer to the General Machinery Manual for additional information on both types of bearings.