Posted by Chuck(G) on March 07, 2003 at 11:04:50:
In Reply to: valve plating posted by frank scoglio on March 07, 2003 at 10:45:40:
I've seen this on other 30's Holtons, so yours aren't unique. (Yes, it's copper). Some time ago, I posted wondering if ultimately this might not be a better idea than nickel plating. Maybe Holton was wondering the same thing or maybe Holton simply wanted to save some money.
My rationale was that nickel is considerably harder than copper, so that wear in a piston valve with nickel-plated pistons would occur primarily on the softer brass valve casing, whereas copper is softer than brass, so that copper-plated pistons would wear in preference to the brass of the casing. It's easy to replace lost material on pistons by replating (you can just about plate copper to any thickness) and simple enough to machine them to tolerances. And ultimately, it's less expensive to plate copper than to plate nickel (nickel plating involves a copper flash coat, anyway).
The downside is that copper is less resistant to corrosion than nickel. But the couple of Holtons I've seen with copper-plated pistons seem not to have suffered much from that.