You can see in
the illustration that this is a five-cylinder engine -- radial
engines typically have anywhere from three to nine cylinders.
The radial engine has the same sort of pistons, valves and
spark plugs that any four-stroke engine has. The big
difference is in the crankshaft.
Instead of the long shaft that's used in a multi-cylinder car engine,
there is a single hub -- all of the piston's connecting
rods connect to this hub. One rod is fixed, and it is
generally known as the master rod.