Introduction: Onan Ky Generator Brush and Slipring Familiarzation
This little KY unit had a damaged engine. The rotor pin was sheared also where it mates to the tapered crankshaft. After repairing and assembling the unit I thought it might be interesting to show what sliprings and brushblocks look like and where they are in this unit. The little KY hides it brushes behind a flywheel on the end of the rotor so it is a little harder than most generators to service the brushes. Due to the unit's weight and varied tools needed most people will find its easier and less frustrating to have this work done at a service center. Besides that you have to remove the unit from its mounting location. That means unhooking AC wiring, DC wiring, Gasoline supply, Exhaust piping and mounting hardware. Not to mention it weighs over 100 pounds. But i will go through the slipring clean process and brush change. The first picture shows the generator with the cover off so you see, from left, engine, generator main body, plastic wind tunneling.
Step 1: The Rotor
This is what the rotor looks like in this unit. It is a hollow shaft with tapered end where the flywheel goes. Then the outer bearing then the brush slip rings. Then the nylon shell where the windings are found. The far right end is an internal taper that seats on the tapered crankshaft end. The pencil point is pointing to one of the two sliprings. These rings are hooked to the windings in the rotor and electricity travels through them from the brushes that ride on them. These rings are dirty and need to be cleaned. The cleaning is easy. Just use a piece of scotchbrite and clean them until they are very shiny. In a later image you will see them clean. To check the rotor just put an ohm meter lead across both rings and see if the reading you have is what the service manual calls for. Usually if a rotor is bad it is because the windings are burned or broken. Then the entire rotor, as a unit, is replaced.
Step 2: The Outter End Housing
This housing is what bolts over the generator main bell housing.
The large hole in the center is where the bearing on the rotor sits. The two bolts the pencil points to is where the Brush block is bolted. The brush block is just a plastic or ceramic housing that holds 2 carbon brushes with wires coming out of them. The brushes are rectangular and made of a carbon material. They constantly rub on the rotor sliprings because they have springs under them in the brush block that push them twords the sliprings. Each brush has a electrical wire coming out of the end of it. That wire has a connector built on it and it connects to a spade on the brush block. The field (+) and field (-) leads from the control module plug on to the same spade as the brush does. So there are 2 brushes. One supply and one return. The wires are all marked on the insulation with letters and numbers. Look where they go before you remove them.
Step 3: Put on the Flywheel.
Once the brush block is in place and everything is rechecked for tightness put on the flywheel. There is a tiny key that aligns the flywheel to the rotor shaft. There is a slit milled in the rotor shaft and machined in the flywheel. The key lines them up. Keys do not hold them in alignment while running. They are only meant to line them up initially. The long bolt that holds it all together is torqued to spec and that torque and the tapered surfaces are what keeps everything aligned while it is running. A magneto is bolted on the end housing and is spaced so it does not rub the flywheel but sits very close to it. The flywheel has magnets in it and they cause a voltage to build in the magneto and this makes the spark to run the engine. The control module can ground out the magneto to shut off the generator if something goes wrong. Now all the plastic is bolted on and we hook up battery and fuel and a meter to see if it all will work. We should see around 120 volts and 60 hertz. There are adjustments on the engine to change its RPM(speed) to correct Hertz if need be.
Step 4: All Done
You can see this is a bit of a project. I did not mention tooling or specs because Those things change as the spec letter changes.
If you decide to try to tackle this buy a service manual. Generators are expensive and must be assembled correctly the first time. You can't unburn windings if something goes wrong. In this unit I had to repair the wiring harness and replace some ends in the control plug that had no pin drag(bad connections). Repair the rotor alignment pin. Repair the engine. This was a 2 month project that I worked on when Time allowed. Everything was checked and ohmed out with a meter. The time and extra checking paid off in the end because it worked first start. I also learned a lot and that made it worth it all.