Wear due to mixed friction

Narrow, wear-free strips at the edges of the bearings

Information on diagnostics

Wear-free strips visible on the edges of the main bearing shells? The central parts of the bearings are black. What happens if there is an axial protrusion of the bearing shells on one or both sides? You can find the information in this article.

Description

Narrow, wear-free strips at the edges of the bearings
No run-in marks visible in this area
Machining structure from production still recognisable in this area
Clear definition between the wear-free strips and the worn area recognisable

Lower main bearing shell Steel-aluminium composite

Two wear-free strips are recognisable at the edges of the bearings without any visible wear marks. The remaining part of the bearing has a slight black discolouration, possibly due to corrosion or wear.

Upper main bearing shell Steel-aluminium composite

One wear-free strip is recognisable at the edges of the bearings without any visible wear marks. The remaining part of the bearing has pronounced scoring.

Assessment

Due to one-sided (Fig. 1) or two-sided (Fig. 2) axial protrusion of the bearing shells, narrow, wear-free strips at the edges of the bearings are formed, which also do not demonstrate the typical adaptive run-in wear. Irrespective of the speed of the journal, there is never any metallic contact in these areas.

Possible causes

Geometric deviations of the journal
Incorrect choice of bearing width
Clearance (shaft/journal misalignment)

Remedy

The bearings can continue to be used depending on their wear condition. They should be replaced as soon as initial rubbing marks develop or indicators of material fatigue become visible and measures to determine the cause should be taken:

Check for correct geometry of the crankshaft before installation: Dimensions, roundness
Replace the crankshaft or install new bearings which fit the crankshaft geometry