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Old 10-13-2012, 07:20 PM
zmelli zmelli is offline
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Join Date: Oct 2012
Location: Norco,California
Posts: 57
Chrome Plating
Moving a notch up the cylinder rework food chain is chrome plating. Here, the worn barrel is ground oversize, and then a layer of chrome is deposited via electroplating to bring the cylinder back to new dimensions. (A good chrome plating job is about .015" thick. A bargain basement one might be a lot thinner.)
Standard pistons can then be used, but chrome cylinders require special cast iron rings (instead of the chrome-plated rings used with steel cylinders). An often-overlooked disadvantage of chrome cylinders is that the relatively soft cast iron rings wear out faster than ordinary chrome rings do.

Chrome is a very hard and durable wear surface—even more so than nitrided steel—and has the additional advantage of being almost immune from corrosion. However, a smooth shiny chrome surface is not oil-wettable, so something must be done to the chrome to allow an oil film to adhere to it.

The traditional solution to this dilemma, used successfully for decades, is channel chrome. In this process, when chrome has been electroplated to the desired thickness, the current flow in the plating tank is reversed for a short (and critical) period of time. This results in a chrome surface that isn't smooth but has numerous microscopic fissures (called channels) that provide a "foothold" for oil to adhere.

There are a couple of problems with channel chrome. The channelling process is apparently more black art than precise science, and it's difficult for even the best plating firms (such as ECI in San Antonio) to get consistent results. If the channels are too shallow, the cylinder won't make TBO. If they are too deep, oil consumption will be high. Even the very best channel chrome cylinders tend to burn a lot more oil than steel.

Lots of folks love chrome. They believe that its durability and corrosion resistance are worth the tradeoff in oil consumption. Chrome is a particularly good choice for operators with extreme vulnerability to corrosion, such as salt water floatplanes and highly seasonal operations.
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