Engine wear - Complex shapes

This document, which is part of a series on the various forms of wear that can affect engines, is the sequel to the for adhesive, abrasive, corrosive and fatigue wear in engines.

It deals with complex forms of wear whose mechanisms involve, as component phenomena, some of the fundamental forms of wear previously described.

Contact corrosion, which is very common in transmission mechanisms and industrial machinery, is also found in engines, where torsional vibrations and crankshaft bending occur. This is why this form of wear can be found on flywheel or pinion crankshaft end fittings, on the dampers of diesel engines, on the backs of bearing bushes when they are poorly adjusted in their housings, on ball or roller bearings, etc.

Cavitation erosion is a form of wear that can occur in two areas of the engine:

• a) in the oil circuit when the engine is running fast and the oil is highly aerated; erosion then affects the anti-friction layers of the bearings;

• b) in the cooling circuit of engines (especially diesel engines) operating under very severe thermal conditions; erosion, which can take on catastrophic proportions such as liner punctures, is mainly localized at the level of the liners, cylinder head and water pump.

Finally, wear of electrical origin, such as electrical pitting or galvanic corrosion, can occur in motors under certain conditions, but almost always remains a second-order phenomenon compared to other forms of wear.