This diagram explains the rotor type pump pretty well. I like to think of it as a kind of “rotational squeegee”. The elliptical on the inside of the circle spins and squeezes the water between the outside of the circle and the housing in a rotational manner, until it reaches the top, where the piston pushes the water up and into the cooling tube.
The piston, what you referred to as “the tab”, should make contact within it’s channel, but if it fits too tight, that part of the rotor will break off. Don’t ask me how I know. The solution is to lightly sand down the sides of the piston, and test fit it so that it just makes contact.
To clean out the cooling system, you’re going to have to remove the powerhead. Once it’s off you can shoot compressed air both up and down the supply tube. Running a long piece of wire up and down the tube will help with any serious clogs. Before replacing the powerhead, but after the rotor is assembled, put a drill on the driveshaft, submerge the gearcase in a barrel of water, and crank the driveshaft clockwise with the drill. This will verify that everything under the powerhead is working, and a good supply of water is making it up to the top of the tube. The powerhead cooling passages also need to be cleared with compressed air.
Improvise-Adapt-Overcome
