Piston Coatings
A major concern for race engine builders and tuners is piston skirt scuffing. Piston scuffing occurs when the piston comes to the top of the cylinder and then changes directions suddenly. The piston skirt compresses the oil film to the extent that it can potentially break through, thus creating metal to metal contact that will eventually lead to wear on the piston and cylinder wall.
A Piston that has a coated skirt has a better piston to cylinder seal, this improved piston to cylinder fit reduces the amount of combustion gases that can blow by the piston and leak into the crankcase.
The application of a permanent low friction coating to the sides of the piston provides a layer of protection against scuffing.
A thermal barrier ceramic-metallic coating for the piston crown is another type of coating that is being used for hi-performance applications. This ceramic heat reflective coating can withstand combustion temperatures of up to 2,000° F and delivers three times the surface hardness of hard-anodized coatings.
By improving the heat retention in the combustion chamber, it will improve thermal efficiency creating more power, in addition to helping the piston run cooler. Too much heat in the combustion chamber also increases the risk of detonation and pre-ignition, so when a ceramic coating is used, the ignition timing should be retarded a few degrees to reduce the risk of detonation and pre-ignition.
A ceramic coating is applied through an immersion process using electrical impulses that convert the piston surface into an extremely strong, smooth and heat resistant ceramic. Because the ceramic barrier is atomically bonded to the piston the material is highly resistant to flaking and cracking and provides exceptional protection even on sharp edges or corners. In addition a ceramic coating can also be applied to a piston's top ring groove to prevent micro-welding.
Conventional piston crown coating technology such as hard anodizing and electroplating produce a lower surface hardness than the ceramic process and are far less resistant to corrosion, cracking, and wear. The use of a ceramic piston crown coating is being used in many high temperature applications such as turbocharged, supercharged and engines using nitrous oxide, in order to aid in the reduction detonation and pre-ignition.