What causes a piston rod to break?


Quick Answer

Thrown rods or piston rod breaks happen due to oil problems, over-revving the engine, faulty piston bearings or normal wear and tear. A thrown rod leads to an engine stopped cold in its tracks.

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Full Answer

A thrown rod pierces the engine block or causes the piston valve and cylinder unit to jam. In either instance, the event is a costly engine rebuild or replacement.

Proper oil level or lubrication prevents friction and engine overheating. Overheating leads to rod failure due to metal on metal friction, warped valves or warped pistons. Carbon buildup also leads to rod failure due to overheating. This problem shows as dark or black-colored oil. Maintaining the proper oil level and using the proper grade of motor oil minimizes these types of rod breaks.

Over-revving the engine can lead to rod breaks. The revving causes rod failure due to a valve's spring failing or being sucked into the engine.

Faulty bearings cause too much play in a crankshaft and stresses the rod. Continued stress causes metal fatigue and eventual rod failure. Engine knock is the usual symptom. Knocking may also mean worn pistons or worn piston valves. In these instances, auto repair sites recommend replacing the piston valve, rod and crankshaft as a unit.

Good auto maintenance extends an auto's life. However, a vehicle's age or high mileage may lead to a rod failure.

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