How do you know when your cylinder needs to be re-Nikasiled?
Sometimes it's not that easy to tell, but usually, you can tell by looking at the cylinder walls. If you can see scratches or chips that are a sure indication that it's time to have your cylinder re-plated. If you can't see any wear or damage that doesn't necessarily mean your cylinder is in good condition. The inside of the cylinder has to be exactly round (to with-in specs) to perform properly. This can only be accurately checked with a dial bore gauge. They can measure to with-in one ten-thousandths of an inch. The Nikasil plating that's on the walls of your cylinder is only a few thousandths of an inch thick but is very hard. It wears extremely well as long as everything is tight and sanitary. If you maintain your engine as the factory recommends it will last for years. However, we all know how easy it is to suck it full of water or dirt or maybe run it low on oil or some other mistake you'll be needing our service. The Nikasil plating, or coating as its sometimes referred to, will have to be stripped and re-plated.
The 'Nikasil' process
The Nikasil surface treatment process was developed in the late 60s by Mahle the German piston manufacturer, in conjunction with NSU and Daimler Benz (468) originally to provide a wear resistant coating for Al alloy rotor casings fitted to Wankel rotary engines. It was the result of a long program of material combinations tried by many Wankel License to overcome a ripple' wear pattern characteristic of this engine type. The process used electrolytic deposition to plate the Al alloy casings with nickel in which particles of silicon carbide smaller than 1 micron (0.001mm) were dispersed. After finishing treatment the plating was only 200 microns (0.2mm) thick in the Wankel application (870). Porsche first used 'Nikasil' coating in a normal piston engine for (air-cooled) Al-alloy cylinders in the 1971 5L development of the F12 Type 912 unit and, compared with the previous Cr-plated Al-alloy cylinders ('Chromal') found it increased power (302). The layer may have been thinner than that used in the Wankel engine (a 'few hundredths of a millimeter' was quoted in (241) when applied in 1973 to the Porsche Type 911/83 competition engine (also air-cooled). The reported improvement in oil consumption of the DFV with 'Nikasil'-treated Al-alloy cylinders may have been a consequence of more rapid and complete bedding-in of the piston rings, which is what is thought to have occurred in the Porsche 912 engine. If this then reduced combustion gas blow-by a power gain would have been observed.