The online magazine on the history and operation of vintage scale model trains in American OO gauge

Tuesday, February 10, 2009

Rotten die castings

One phenomena seen more often than I would like among old die castings is what I loosely call “rot.” The more formal term for this process is zinc pest, described in this Wikipedia article. For example see the castings below, which I came across again last week when I was working on wheelsets and trucks for several passenger cars.

These are all the sideframes from a pair of Famoco four wheel passenger car trucks. Two are exactly as Famoco intended and the other two presumably left the factory looking exactly the same but deteriorated into being totally unusable for anything at all. This is primarily a result of impurities in the alloy used for the die casting.

As to prevention, I figure that if it is going to happen to any old OO part it has happened already, although humidity is thought to contribute to zinc pest as well. If it looks good now, it probably is good for as long as we will be around to enjoy the parts.

These trucks came in a kit I was given when I was just starting out in OO, a Famoco combine kit, which I built up (one of the few that I built up from new—a topic for another day). As the two sideframes were bad, as an experiment I put the Famoco wheelsets in a pair of S-C trucks that were on hand. The result was a pair of trucks that roll great! It is not uncommon to see S-C trucks of all styles with the wheelsets switched out with solid axle wheelsets of different manufacture. The result is the Famoco wheelsets that were shipped with the sideframes in the photo are on one of five heavyweight passenger cars on the layout right now, rolling well and looking great behind the E-7A.

UPDATE: See this article for more information

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