Information on diagnostics

Wear due to mixed friction

Stripe-like wear in the centre of the bearing

What is ridge wear on engine bearings? What happens if the oil bore is insufficiently rounded? Where do the strips in the centre of the bearing in the lower main bearing shell come from? How is the oil groove in the upper main bearing shell involved? Find out here.

Description

  • Stripe-like wear in the centre of the bearing as a continuation of the oil groove – in both bearing shells in the area of the oil bore on the journal in the case of connecting rod bearings
  • Sometimes with circumferential scratches
  • Less worn bearing edges
  • Highly localised zone of wear
  • In severe cases: signs of material fatigue and initial rubbing marks visible

Lower main bearing shell Steel-aluminium composite

Clearly delineated stripes can be seen in the centre of the bearing. This corresponds to the shape of the oil groove which is in the upper main bearing shell. The wear marks occur in the form of adaptive run-in wear.


Assessment

This type of wear may be due to a lacking or insufficiently rounded oil bore (Fig. 1). With this in mind, the wear in the lower bearing shell in main bearings or in both bearing shells in connecting rod bearings is very pronounced in the area of the oil bore on the journal.

A second way in which wear arises that can lead to the same damage symptoms is ridge wear (Fig. 2). This results from the lower journal wear in the area of the oil groove. Since there is no metallic contact between the journal and bearing due to the oil groove, no material removal takes place and a ridge forms on the journal. This ridges leads to stripe-like wear in the bearing shell without an oil groove. Both processes can lead to initial rubbing marks and fatigue damage.

Possible causes

  • Lacking or insufficiently rounded oil bore (Fig. 1)
  • Unfavourable material combination of the bearing and journal leads to lower journal wear in the area of the oil groove (Fig. 2)

Fig. 2

(1) There is no metallic contact in the area of the oil groove in the upper main bearing shell. The journal wear is lower than in the areas in contact with the bearing surface.

(2) A very small ridge can form due to the reduced journal wear in the area of the oil groove (shown exaggerated here to aid understanding).

(3) In the lower main bearing that does not have an oil groove, this ridge causes increased wear in the centre of the bearing. This leads to the typical stripelike wear pattern in ridge wear.


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 and reworking of the oil bore outlet
  • Check shaft journals for ridges in the area of the oil groove
  • Check material combination of the journal and bearing (hardness of shaft/bearing)
  • Check roughness of the journal

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