Friday, January 18, 2008

Piston Acne

When I last wrote on the topic of A&P school, we had removed the O-320 from the Piper Cherokee in order to tear it down and see if we could determine why it was eating its sparkplugs. Since then, we've removed the cylinders and pistons, all of the accessories, and split the crankcase. We were careful to look for foreign objects in the cylinders and/or exhaust as we did so, but found nothing. What we did find was that in cylinders 1, 2, and 4, the pistons, the valves, and the inner surfaces of the cyliner heads were beat to hell and back. They look like an over zealous antique furniture counterfeiter went after them with a small length of chain. Every inch of the surfaces was nicked and scratched. If you imagine what it would look like if you tossed a hardened steel washer into the cylinder and ran it for an hour, you have a good idea of what condition these parts are in. And, we have no way to explain what happened!

We're going through the instructional exercise of precisely measuring all of the innards, determining a multitude of arcane things like washout, rod bearing journal diameters, piston pin diamter, etc. before putting it all back together. With the limited budget the school has, there's no way that they're buying new pistons and cylinders, so we're going to reassemble it with the ones we have and hope that it runs. The reassembly is not going to be easy; the same level of conscientious marking of parts and their locations that was exhibited when removing the engine from the airplane (which is to say "none") went into its disassembly. Nuts, bolts, clamps, etc. are all neatly piled in abject disarray in a tin pan. It's going to be interesting trying to sort all of that out!

No comments:

Post a Comment