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Engine piston: replacement and selection

When and why it is necessary to replace engine piston

The engine pistons have no specific lifetime limit. Usually, they are replaced in case of deformation, breakage, burning-out, wear of the mounting hole of the piston pin.

Appearance of piston defects is caused by the following: insufficient or low quality of lubrication, impacts of foreign objects (such as split-off part of the connecting rod, crankshaft or valve), hydraulic shock caused by ingress of water into the cylinders (for example, after driving through a deep puddle). Deformation of the pistons can occur due to usage of spare parts with excessive head height, or due to insufficient sealing of the cylinder head when doing major engine overhaul. Breakage can occur as a result of collision of the pistons with valves, when too high rotation speed of the crankshaft doesn’t allow to pull the valves back, and due to detonation in the cylinder.

Signs of components defects are pistons knocking, especially at engine warming up, and rattling sound of the warmed up engine.

The pistons are replaced in a set. Also, during their replacement you need to install new piston pins and rings. The connecting rods are also replaced if necessary. After all works finishing, you need to carefully use the engine for about 1,000 – 2,000 km, avoiding wheel slipping, high rpm and heavy loads transportation.

How to select piston

The pistons differ by production method, and can be die-cast or forged. For production of the first type components high-pressure casting is used. The forged pistons are made by stamping method; they are more durable and less apt to heat expansion. As a rule, the forged pistons are installed in turbocharged engines. Their price, higher than that of the die-cast pistons, can be considered as their disadvantage.

The shape of the piston top (piston head top surface) depends on the type of the engine, on configuration and volume of the combustion chamber, location of the valves, aspects of fuel-air mixture supply into the chamber, and other factors. In gasoline engines the piston top is flat or with recesses responsible for full opening of the valves. There are combustion chambers made in piston tops of direct injection diesel engines. Their shape allows to provide better whirling and formation of mixture.

The components which are able to perform their functions for a long time, are produced by well-recommended manufacturers only. Kolbenschmidt, Mahle Original, Nural, IPSA, Et Engineteam and others are amongst them.

Select the components strictly for your engine. This will help to avoid incompatibility of the parts by diameter, length, compression height, weight and other factors, important for engine operation. Beside that, a high quality parts kit for the exact car will include the piston pins and bushes. Sometimes, a set of the piston rings can be added.