You can remove the flywheel, magneto, spark plug, muffler and centrifugal clutch and what you are left with is the combustion chamber, piston, connecting rod and crankshaft. If you remove the crankshaft cover, you expose the crankshaft, as seen in this photo:
The two ends of the crankshaft run on roller bearings, as seen here:
If you pull on the crankshaft, the piston comes with it:
This piston is 1.5 inches (38.1 mm) in diameter and 1.5 inches high.
The connecting rod connects the piston to the crankshaft. A set of roller bearings keeps everything smooth at the crankshaft end.
So there you have it -- a complete chain saw! It is a miracle of modern manufacturing technology that you can buy one of these, containing several hundred parts, for about $100. And it will run really well for years with little or no maintenance.
For more information on chain saws and related topics, check out the links below.