|
Last week the pistons got cleaned up and measured.
The pistons are cast iron with cast iron rings. You'll remember that the cylinders are cast iron, too.
The pistons have a threaded hole in one piston pin boss, for a special bolt. This retaining bolt has threads right under the head, but a smooth shank for the piston pin.
The bore is nominally 90 mm, and the piston pin is about 16 mm diameter.
One of the six pistons was damaged, with a chip in the bottom edge. Fortunately we have a set of new pistons available. Unfortunately some of them have similar damage. There appear to be enough intact pistons to choose from, though.
You'll see that the rings are identical, and that their ends have a smoothly-shaped overlap. The workmanship of the original machining is outstanding throughout the engine. Still, almost every part is marked for its location because the part sizes, one to another are not close enough to be interchangeable - at least not that we've seen yet. Since some parts aren't numbered, and of course the replacement parts are unmarked, we've been tagging and bagging every part.
This engine appears to be a first-run engine. That is, it hasn't had an overhaul before. We were debating how much run time the engine has, and suspect that it's not a whole lot.
One thing that I forgot to mention in an earlier posting is that each cylinder has two spark-plug holes. Since the engine is a single-ignition engine, that wsa at first confusing. Then I noticed that there were blind plugs in all the lower holes, with spark plugs in all the upper holes. In this fixed radial engine, that tends to prevent oil from fouling the plugs when it's not running.
Conveniently, the spark plug holes fit the same size spark plugs as my Continental O-470 engine on my Cessna Skywagon. That suggests that we should be able to find some suitable spark plugs later on.
.
|