Information on diagnostics

Overheating damage on engine bearing

Cracks are visible on the edges of the bearing shells. The sliding layer is significantly discoloured. What are the reasons? White fusion deposits visible in the galvanic layer of the bearing shell? What are causes of heat cracks and fusion deposits on engine bearings? Find out here.

Introduction

Overheating damage is the result of dramatic temperature development in the engine bearing shell, which goes hand-inhand with acute mixed friction. This is why heat cracks, discolouration and fusing are also always displayed for initial rubbing marks or seizure.

The heat dissipation provided by the lubricant plays a central role here. If heat dissipation is no longer provided, this causes complete failure. Even with the initial signs of overheating, local changes to the microstructure occur and the integrity of the material is reduced. Heat cracks form at the affected areas.

Possible causes

  • Consequential damage due to increasing temperature development as a result of initial rubbing marks, seizure or edge wear
  • Insufficient heat dissipation provided by the lubricant (see chapter: "Possible causes – initial rubbing marks")

Remedy
If overheating damage occurs, the bearing must be replaced and the causes investigated. In the event of consequential damage, the cause of the primary damage must be rectified. If no further damage to the bearing is visible, the lubricant circuit (see chapter: "Initial rubbing mark remedy") and the stress on the bearing must be checked.

Heat cracks

Description

  • A network of cracks is visible
  • Fusing and discolouration of the bearing shell

Fusing of the sliding layer

Description:

  • Material displacement and smearing visible in the sliding surface
  • Accompanied by heat cracks and discolouration of the bearing shell

Discolouration of the sliding layer and/or the back of the bearing

Description

  • Blue-ish to black discolouration of the sliding layer or on the back of the bearing
  • Accompanied by lumps and material removal/displacement

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