Since this project bike was not running when I picked it up and had been sitting outside for awhile, I don’t know what components of the electrical system work. So I remove the starter motor and test it.
This is a short summary video showing how I do this work.
VIDEO: 1983 BMW R80ST Remove And Test Starter Motor
Remove Starter Motor
The motor is secured by two bolts and locking nuts at the rear and by a single 10 mm bolt that secures the front motor bracket to the engine block. I can access the front bracket bolt by removing the front engine cover.
Whenever you remove the front engine cover, ALWAYS be sure you remove the battery (-) ground cable from the battery. If the cover touches the diode board at the top of the engine it will short it out and you will have to replace the diode board.
The rear bolt heads are captive against the side of the starter motor so I can remove the lock nuts with 13 mm socket. However, my standard 3/8″ drive 13 mm socket will not fit on the right locking nut (as viewed from the rear of the engine), so I use my 1/4″ drive 13 mm socket which has a thinner wall to remove it.
I remove the large nut on the front of the starter solenoid to detach the large battery (+) cable and the smaller red wire with the ring terminal that are secured by the nut. Then I remove the black wire from the spade terminal on the starter solenoid.
To remove the motor I twist it so the starter solenoid on the front right side of the motor is facing up and tilt the motor clear the semi-circular cutout in the top of the engine and then position it so I can get the front motor bracket to clear the top of the engine block.
Clean And Inspect The Starter Motor
The motor looks to be in good condition as there are no signs of rust on it and the paint is in good condition.
I remove the front bracket by removing the two mounting nuts with an 8 mm box end wrench. Under the nut is a wave washer that sits on top of a smaller flat washer against the bracket. There is also another flat washer behind the bracket on the mounting stud in the starter motor housing.
I clean the starter motor in my parts washer and use compressed air to blow it dry. These are the markings on the starter motor and the starter solenoid that is attached to the body of the starter motor.
I use Auto Sol metal cleaner with 0000 steel wool to remove the deposits and tarnish from the bracket. The plating is intact and not rusty so I don’t have to paint it. I also use the 0000 steel wool with Auto Sol metal cleaner to clean the starter motor nose housing that goes over the Bendix gear on the rear of the starter motor. The plating on it is also intact with no rust.
I reinstall the front starter motor bracket with the step on the bottom of the bracket toward the rear of the starter motor.
I also clean the top engine housing the starter motor sits inside of with Gunk engine cleaner, a brass brush and 0000 steel wool. It had crud and leaves inside it.
Testing The Starter Motor
I mount the starter motor in my vise with the rubber jaws. I use two battery (+) cables to attach a battery to the starter motor. I attach the (+) cable to screw terminal with the large nut and to the RED battery (+) terminal. I attach the other cable to the starter motor bracket using a bolt and nut and then to the battery (-) ground terminal.
Don’t let the ends of the cables touch each other after they are attached to the battery as it likely will damage the battery.
I attach a wire to the spade terminal where the BLACK wire was attached. The BLACK wire comes from the starter relay and powers the starter solenoid so it will close sending power to the starter motor. When I touch the wire to the starter solenoid screw terminal with the large nut, it will send power to the starter solenoid, just like the starter relay would and the starter motor should turn and the Bendix gear should spin and move outward.
At first the motor didn’t work. I checked all the electric connections and found some corrosion on the end of one of the cables. I cleaned it off with some steel wool, reattached it and then the motor worked. 🙂
And here is the starter motor compartment after I cleaned it up.
2022-03-29 Corrected document subsystem from “61-Electrical” to “12-Engine Electrics”