bigger piston, bigger bore

I picked up the '68 Vespa Super 125 knowing the piston was seized. As you can see in this video, the piston seized in the cylinder and they both move back and forth with the movement of the flywheel. 

I was helping Scooter Steve move more of his shop from Austin to Buda today. As we worked out way through piles of scooters and motorcycles and engines and tires and mufflers and such, Steve pulled out a box of cylinder barrels. Inside was this set. It's a 150cc and we checked it against the Super 125 when we got back to my house and it looks like it will bolt right on. There were some rings in with the piston but I will replace those along with some bearings while I am at it. 

On the left is the cylinder barrel. The flange off to the left fits inside the engine. The flange off the bottom is the exhaust. In the upper center is the piston which travels back and forth in the cylinder. The cap on the right is the cylinder head. The spark plug screws into the threaded hole. The pieces are bladed to help dissipate high heat from the cylinder. 

The piston is in pretty good shape if a little dirty with carbon on the top. 

The cylinder is nice and smooth. Scoring on the side would indicate a damaged piston or damaged rings. 

Here is the piston in the cylinder and the combustion chamber on the right. Vaporized air and fuel enter the cylinder as the piston is moving towards the spark plug. This compresses the mixture and the spark from the plug ignites it. BOOM! The piston is pushed back down the cylinder. 

With bad rings or a damaged cylinder, the fuel/air mixture could not be compressed as tightly and the combusting fuel on the opposite stroke could escape past the rings causing less power pushing the piston back.

This stuff seems like it's in good condition. Now to remove the old cylinder and piston. Steve and I are going to try a C-Clamp style tool to manually push the piston out. Then it's just a matter of cleaning it up, setting it straight, lining it out, doing the work, killing some chickens, washing some hands, maybe some beer.