Nickel Process
The Nickel process is a nickel alloy cylinder bore coating. After electrochemically depositing the nickel-silicon carbide composite, the cylinder bore is machined to size and given a ring finish. Nickel costs more than the channel chrome process but offers excellent performance and wear characteristics with quick break-in, lower oil consumption and operating temperatures than chrome. Nickel is rapidly replacing chrome as a plating choice for aircraft cylinders.

Channel Chrome
Channel chrome is a process that was invented around World War II for refurbishing military aircraft cylinders and is known for its excellent wear characteristics.

Channel chroming involves the preliminary grinding of the cylinder bore until a smooth surface and perfectly round bore is attained.  Hard chrome is then applied through electroplating until the specified dimensions are reached.  All cylinders cannot be chromed.  Deep pits or previous oversizing of the bore can cause rejecting of the cylinder. 

Near the end of the process, the electrical current is reversed in order that 'cracks' or channels can form.  Since chrome is harder than steel and does not absorb oil, these channels are critical for essential lubrication. The density of the channels is called porosity and the area between the channels are called plateaus.  The depth and number of channels is important.  Too many channels will result in too much oil consumption and inhibit proper break-in while too few channels will prevent adequate lubrication. 

It is important that the initial break-in procedure for channel chromed cylinders be performed properly.  Failure to do so may cause difficulty in achieving ring seating and result in excessive oil consumption.  If rings have not seated within 25 hours, oil turns black rapidly after changes and oil consumption is high, it may become necessary to remove and re-hone the cylinders and install new rings.

Always use cast iron rings for any chrome bore. Chrome-faced rings or rings intended for steel bores will cause immediate cylinder wall failure.  This is a very expensive mistake.

Nu Chrome
Nu chrome is a process invented to improve upon channel chrome by eliminating the break-in problems sometimes associated with channel chrome.  The term 'Nu' is a trade name.

With Nu chrome, the cylinder goes through the same plating procedure as with channel chrome until the stage where the channels are created.  The cylinder is then removed from the chroming tank and a silicon carbide mixture is mechanically honed onto the surface. This silicon carbide layer is approximately .001 to .005 thick.  The result is a surface that absorbs oil and is slightly abrasive thereby facilitating lubrication and ring break-in.