Initial rubbing marks

• Bright, smooth marks of mixed friction, above all in the main load area
• Sliding layer displaced into the relief area, mostly in the direction of rotation and tongue-shaped
• Scoring

Initial rubbing marks may result from run-in marks if the effect of mixed friction intensifies. If this is a temporary state, these may be levelled out again; the functionality of the bearing is not further impaired. Assessing this is very difficult, however. If the mixed friction state is continued, the initial rubbing marks are strengthened and scoring at the journal may occur. The result is seizure at the affected bearing shells, whereby the bearing shell welds with the journal due to thermal stress.

• Oil bores not free: the reason may be the incorrect installation of the bearing shells or blockage of the oil bores – the latter is often the case when biological fuels are used
• The lubrication gap is too small, meaning that a stable lubrication film cannot be formed – cause: form and geometry deviations of the shaft or journal, or bending of the crankshaft
• The lubrication gap is too large, meaning that the hydrodynamic pressure required for the formation of the stable lubricating film is not achieved
• Oil level or oil pressure too low
• Blocked oil filter
• Defective oil pump
• Leak in the oil lines
• Overstressing of the bearings: the strain is higher than the bearing is designed for – causes are chip tuning or piston seizure, for example
• Effect of particles: particles find their way into the bearing gap, causing initial rubbing marks on the journal and bearing. In the event of embedding or scoring, edges are created, resulting in greatly increased mixed friction

Initial rubbing marks may continue to develop into seizure of the bearings. It is therefore important to replace the bearings and to rectify the cause:

• Check that all of the oil bores are free and that there is no blockage
• Check the actual bearing clearance: if it is not within the tolerance range, form and geometry errors are often the cause
• Check the functioning of the oil filter and always change the oil filter and oil according to the manufacturer‘s instructions
• Check the oil level and oil pressure and readjust if necessary
• Check the oil pump is functioning
• Check the oil lines for any leaks
• Check the stress of individual bearings
• Check the entire bearing set for the embedding of particles or grooves. If present, the influence of particles may have caused the formation of the initial rubbing marks