This “project” bike has been sitting for over 25 years. So, for reliability, I’m going to replace the charging system which consists of the alternator, diode board and all associated wiring. I may try to rebuild the electronic ignition sensor, aka, the “bean can” that uses a Hall effect sensor to trigger the ignition. This document covers how I remove the components.

Also, I plan to replace the timing chain, crankshaft timing sprocket and the nose bearing which are behind the inner timing cover that the charging system and electronic ignition sensor are mounted to, so I have to remove all these components before I can remove the inner timing cover.

The original alternator looks a bit bedraggled.

I’ve replaced charging systems on other projects. Here are links to those documents.

• 12 BMW 1977 R100RS Replace Engine Electrical Components
• 12 BMW 1983 R100RS Remove Diode Board, Alternator & Electronic Ignition Sensor

Tools

I use a special hardened bolt to pull the alternator rotor off the crankshaft nose. I got this from Euro MotoElectrics, EME Part# BOALT-Rotor642Tool.

Video

Here is a short video showing a summary of how I do this work.

VIDEO: 1983 BMW R80ST Remove Alternator, Diode Board & Electronic Ignition Sensor

Removing Charging System Components

I removed the engine from the frame, but this work can be done with the engine in the frame. Under the front engine cover are the rectangular diode board above the circular alternator which constitute the charging system.

WARNING:
Always remove the battery ground wire BEFORE removing the front engine cover. If the cover contacts the diode board it will ruin the diode board.

Remove Diode Board

The diode board is above the alternator. I start by disconnecting the two wires on the sides of the diode board. The left side wire goes to the “Y” terminal of the alternator on the stator cover. The right side wire goes through a hole in the black timing cover and connects to the large screw terminal on the starter motor. Since I previously removed the starter motor, the other end of this wire is already detached. You can see how I remove the starter motor here.

• 12 BMW BMW R80ST Remove And Test Starter Motor

I remove the four Allen bolts with wave washers that mount the diode board to the black timing cover.

I turn the diode board over to access the back of the board. There is a large connector in the middle of the board that supplies ac current from the output of the alternator to the diode board. There are three wires attached because the alternator produces three-phase ac current. There is also a plug on the left side of the board with a BLUE wire that goes to the voltage regulator that controls the output of the charging system. I disconnect them to remove the diode board.

Remove Alternator

The alternator has a stator cover that the stator coil attaches to and a rotor that is a press fit on the crankshaft nose and spins inside the stator coil. I remove the stator cover and stator coil by removing the three small Allen bolts that secure the stator cover to the black inner timing cover.

Then I pull the stator cover and stator coil off exposing the rotor.

The alternator rotor has two copper slip rings and is held on the crankshaft nose with an Allen bolt.

I use an oil filter wrench to to clamp the outside of the rotor to keep the crankshaft from turning and use my electric impact driver to loosen the rotor bolt. You can use an Allen socket to loosen the bolt as well, but I’m lazy. 🙂 When the bolt is loose from the crankshaft, it won’t come out because there are also threads in the rotor, so I unscrew it by hand from the rotor.

Then I screw in the special rotor removal bolt and again use the oil filter wrench on the outside of the rotor to keep the crankshaft from turning. I use an Allen socket to tighten the special rotor removal bolt. The rotor is secured on the crankshaft taper by friction using what is called an interference fit, so it often makes a bang when it comes loose.

Remove Electronic Ignition Sensor

There is a plug that connects the wires in the electronic ignition sensor to the ignition control unit. The plug is secured with a wire bail that I remove with a small screw driver by prying the wire out of the slot in the plug.

The electronic ignition sensor, also called the “bean can” because it looks like one, is secured by two Allen bolts with a wave and flat washer. I remove them and then pull the bean can out of the hole in the inner timing cover.

There are ears on the end of the electronic ignition sensor that engage with slots on the end of the camshaft and there is a large O-ring on the electronic ignition sensor to seal the sensor so oil doesn’t leak. I’ll replace the O-ring with I install the bean can.

Here’s what the inside of the front engine cover looks like now with the engine electrical components removed from the face of the inner timing cover.