Radial Engine Question

[TXGunNut]

Headed down to Cabelas about the time the Blue Angels started their show at Alliance Airport yesterday. Those guys really know how to put on an exhibition of skill and sheer horsepower!
It reminded me of something I saw when I worked airshows and often found in the static displays. I've always enjoyed the static displays, especially Confederate Air Force, almost as much as the aerial displays.
I've seen something on several of the radial engines that intrigued me. One the front of the engine, below the crank and secured with safety wire over what looked like an expansion plug I sometimes spotted a penny. A friend who dabbles a bit in old planes suggested the date of the penny was the date of the last overhaul but he wasn't sure.
Anyone know? For all I know it's a lucky penny and nothing more but I think there's a story behind this engine builders' little touch.

[HarryT]

Superstition

[Petrol & Powder]

A quick search of the internet (if it's on the internet it must be true....right?) yields two different stories.
1. Pratt & Whitney, maker of a large number of radial engines placed pennies on the engines during manufacture and the tradition caught on. When engines were overhauled the mechanic would return the same penny to the engine.
2. Pennies were replaced with the current year penny when the engine was overhauled.

Some people claim to have seen pennies on engines that had been manufactured and immediately stored (never used) which lends credence to the first theory.

Both theories seem to be just that, theories.

[PULSARNC]

Asked the owner of Texan about that recently He told me the penny end always from the year the airplane was manufactured just something some one did in ww2 and it caught on and is commonplace now