PISTON FAILURE

PISTON - HOLE IN

If the damage is concentrated on the crown of the piston it is usually foreign material entering the combustion chamber or a failure of a cylinder head component such as valve or valve seat. Ample evidence can usually be gathered by close examination of the head, carburettor and intake system.

Often the failed part may belong to another cylinder but finds its way via the intake manifold.

Detonation or pre-ignition is the other cause. In petrol engines the causes for detonation are usually, over advanced ignition timing (base or total advance), compression too high or incorrect octane rating of the fuel.

Excessive deposits of carbon or hot spots in the combustion chambers (sharp edges that are thin enough to glow red-hot and cause pre ignition). Incorrect spark plugs, spark cross firing and incorrect air/ fuel ratio can also can result in pre ignition. Diesel engines suffer the same type of damage and is usually caused by faulty injectors, injector pump or pump timing.

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Piston damage due to timing chain failure

Hole in piston crown due to valve failure