12 BMW BMW R80ST Remove And Test Starter Motor

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.

What The 1983 R80ST Looked Like When I Found It

What The 1983 R80ST Looked Like When I Found It

Video

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.

DANGER:
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.

Starter Motor Rear Mounting Bolts

Starter Motor Rear Mounting Bolts

Front Engine Cover Removed

Front Engine Cover Removed

Front Starter Motor Bracket 6 mm Mounting Bolt

Front Starter Motor Bracket 6 mm Mounting Bolt

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.

3/8 Inch Drive 13 mm Socket Fits On Left Nut

3/8 Inch Drive 13 mm Socket Fits On Left Nut

1/4 Inch Drive, Thin Wall 13 mm Socket

1/4 Inch Drive Thin Wall 13 mm Socket

1/4 Drive Thin Wall 13 mm Socket Fits Right Nut Which Is A Tight Fit

1/4 Drive Thin Wall 13 mm Socket Fits Right Nut Which Is A Tight Fit

Rear Starter Motor Bolt Lock Nuts

Rear Starter Motor Bolt Lock Nuts

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.

Battery (+) Cable

Battery (+) Cable

Battery (+) Cable Removed From Starter Motor Solenoid Threaded Terminal

Battery (+) Cable Removed From Starter Motor Solenoid Threaded Terminal

Diode Board Red Output Wire From (B+) Terminal

Diode Board Red Output Wire From (B+) Terminal

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.

Pulling Starter Motor Out So Rear Motor Bracket Clears Engine Housing

Pulling Starter Motor Out So Rear Motor Bracket Clears Engine Housing

Pulling Starter Motor Out So Front Bracket Clears Engine Housing

Pulling Starter Motor Out So Front Bracket Clears Engine Housing

Starter Motor Removed

Starter Motor Removed

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.

Removing Starter Motor Front Bracket

Removing Starter Motor Front Bracket

Starter Motor Front Bracket Hardware Detail: Nut. Wave Washer & Flat Washer Go On Front Of Bracket

Starter Motor Front Bracket Hardware Detail: Nut. Wave Washer & Flat Washer Go On Front Of Bracket

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.

Starter Motor Markings

Starter Motor Markings

Starter Solenoid Markings

Starter Solenoid Markings

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.

Using Auto Sol Metal Polish With "0000" Steel Wool

Using Auto Sol Metal Polish With “0000” Steel Wool

Using Auto Sol Metal Polish With "0000" Steel Wool

Using Auto Sol Metal Polish With “0000” Steel Wool

Starter Motor Front Bracket Refinished

Starter Motor Front Bracket Refinished

Starter Motor Nose Refinished

Starter Motor Nose Refinished

I reinstall the front starter motor bracket with the step on the bottom of the bracket toward the rear of the starter motor.

Front Starter Motor Bracket Refinished

Front Starter Motor Bracket Refinished

Orientation Of Starter Motor Front Bracket

Orientation Of Starter Motor Front Bracket

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.

Top Engine Housing Is Clean

Top Engine Housing Is Clean

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.

DANGER:
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.

Starter Motor Mounted In Vice With Rubber Jaws

Starter Motor Mounted In Vice With Rubber Jaws

Starter Motor Solenoid Terminals

Starter Motor Solenoid Terminals

Battery (+) Cable Attached To Threaded Terminal With Large Nut

Battery (+) Cable Attached To Threaded Terminal With Large Nut

Battery (+) Cable Attached To Battery (+) Terminal (RED)

Battery (+) Cable Attached To Battery (+) Terminal (RED)

Battery Cable Attached With Bolt To Starter Motor Bracket To Act As Ground

Battery Cable Attached With Bolt To Starter Motor Bracket To Act As Ground

Battery Ground Cable Attached To Battery (-) Terminal

Battery Ground Cable Attached To Battery (-) Terminal

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.

Applying Power To Starter Solenoid

Starter Motor Bendix Gear Inside Nose Moves Outward When Motor Turns

Starter Motor Bendix Gear Inside Nose Moves Outward When Motor Turns

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.

Top Engine Housing Is Clean

Top Engine Housing Is Clean

Revisions

2022-03-29  Corrected document subsystem from  “61-Electrical” to “12-Engine Electrics”

2 thoughts on “12 BMW BMW R80ST Remove And Test Starter Motor

  1. It’s great to see normally static displays that are now in visual action. Good write up and visual displays. Thank you so much for all your work and time, Brook.

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