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Both rod and main bearings must feature a specified amount of crush area in order to achieve bearing lock-in within the housing.
The bearing shell outer edges (approaching the parting line areas) are larger than the saddle, which adds to the lock-in placement of the bearing shells.
Dirt particles or embedded blasting shot left behind in the housing face can push the bearing inward, creating a high spot between the bearing and shaft, which leads to damage of the bearing’s outer layers. This will restrict oil clearance and can cause localized overload, friction, heat and will lead to bearing failure.
Oil film is formed during shaft rotation. As rotation begins, the oil film is generated, which travels around the circumference of the shaft, literally lifting the shaft into a centered location.
This view shows the damage that results from trapped particles behind the bearing. Note the bearing wear on the face (left). A metal chip that was trapped behind the bearing during assembly distorted the bearing wall inward against the shaft, causing wear through the overlay into the copper-lead base.
Through the analyzing of elasto-hydrodynamic lubrication (EHL), we see the difference in oil pressure peaks with H-beam (left) and I-beam connecting rods.
During TDC on the exhaust stroke, the bearing housing may begin to elongate, creating a greater bearing clearance at the top of the rod bearing.
Bearing cavitation damage can begin to occur when the shaft pulls away from the oil film abruptly, creating vapor bubbles. Once the bubbles break, this cavitation erosion can slowly begin to erode the bearing face.
This view shows the bearing construction of a Clevite TriArmor bearing, including the steel backing, cast copper/lead layer, babbitt outer layer and the moly/graphite surface coating.
Moly/graphite anti-friction coating needn’t be applied to the thrust faces of main bearings, since it’s common for builders to fine-tune crankshaft thrust by sanding the thrust surface of the bearing.
Tags: BEARING DAMAGE, BEARING ELONGATION, BEARINGS, CAVITATION, CLEVITE TRIARMOR, COATINGS, CRUSH AREA, ELASTO-HYDRODYNAMIC LUBRICATION, H-BEAM RODS, I-BEAM RODS, MOLY GRAPHITE, OIL CLEARANCE, OIL FILM
