Car piston

How to detect the engine piston failure

The part’s state can be assessed in the course of the cylinder-piston group comprehensive check performed at a service station. First, using appropriate equipment, the cylinder compression and the crankcase gas blowby are measured, and the combustion chamber tightness is checked. After this, if necessary, the engine is dismantled and the damage assessment of its components is performed.

At a DIY check, ask your assistant to start the engine, turn on the idle speed, and then sharply press the accelerator pedal. At the same time apply a blank paper sheet to the exhaust pipe. Oil stains on the paper surface often indicate the cylinder-piston group wear.

You may identify that the piston needs to be checked by the following signs:

• oil consumption has increased;
• engine power has decreased;
• a blue-gray or black smoke comes out of the exhaust pipe;
• spark plugs are covered with carbon deposit;
• oil is detected in the air filter or the connecting pipe;
• at idle the engine is unstable, and the gear shift lever vibrates.
• abnormal sounds are heard when the engine is running, increasing at low rpms or under loads.

Causes of piston failures

Any situation where the processes occurring in the combustion chambers are violated is dangerous for the piston. For example, a fuel-air mixture may burn longer than usual because of faults in the fuel supply or turbocharging systems, or due to the air filter delayed replacement. This may result in the melting of the piston bottom surface. And the use of a low-octane gasoline causes detonation in the engine, which leads to the metal erosion and its destruction.

The clearances between the part and the cylinder, improperly adjusted during the factory assembly, result in the piston skirt premature wear. The same effects can be caused by engine overheating.

Lack of oil or too low pressure in the lubrication system are destructive for the piston: the absence of an oil layer between the metal surfaces leads to their overheating, melting and jamming. Neglecting the lubricant replacement schedule provokes the engine ducts contamination and the accelerated wear of the movable joints.

Worn out, warped or cracked piston rings cannot ensure reliable sealing. The hot gases blow through the formed gaps, which leads to burning of the oil film on the cylinder walls. This results in scoring of the piston surface.

Ingress of foreign objects into the combustion chamber leads to the part mechanical damage: chips, cracks and holes.

Repair of the piston

In some cases, the metal sputtering method is used to restore the part surface and its original dimensions. First, damaged spots are cleaned and then covered with a special compound. Once it has hardened, the built up area should be ground, with shearing the excess with a cutter.

Sometimes, to reduce the clearances and improve the tightness of the parts fit, a special spring ring is installed in the worn out groove of the piston together with a piston ring.

Replacement of the piston

If the part is not repairable, the piston should be replaced with a new one. The repair part size is usually bigger than the nominal, so during the installation, the components should undergo turning. In most cases, cylinder boring and honing are also required. The piston replacement should be performed exclusively at a service station.