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

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.

Original Alternator Looks Bedraggled

Original Alternator Looks Bedraggled

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

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.

Alternator Rotor Removal Bolt

Alternator Rotor Removal Bolt

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.

Diode Board (Top) & Alternator (Below) Are Inside The Front Engine Cover

Diode Board (Top) & Alternator (Below) Are Inside The Front Engine Cover

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.

Alternator "Y" Terminal Wire Between Diode Board and Alternator

Alternator “Y” Terminal Wire Between Diode Board and Alternator

Diode Board DC Output Wire To Starter Solenoid Terminal

Diode Board DC Output Wire To Starter Solenoid Terminal

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

Removing Diode Board Allen Bolts

Removing Diode Board Allen Bolts

Diode Board Hardware Detail

Diode Board Hardware Detail

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.

Plug With Three Wires From The Alternator

Plug With Three Wires From The Alternator

Plug With Blue Wire To The Voltage Regulator

Plug With Blue Wire To The Voltage Regulator

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.

Stator Cover Hardware Detail

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

Alternator Stator Removed

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

Alternator Rotor 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.

Using Oil Filter Wrench & Electric Impact Drive To Loosen Alternator Rotor Bolt

Using Oil Filter Wrench & Electric Impact Drive To Loosen Alternator Rotor Bolt

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.

Install Special Rotor Removal Bolt

Install Special Rotor Removal Bolt

Remove Alternator Rotor With Oil Filter Wrench And Allen Socket

Remove Alternator Rotor With Oil Filter Wrench And Allen Socket

Crankshaft Nose Taper

Crankshaft Nose Taper

Taper Inside Alternator Rotor

Taper Inside Alternator Rotor

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.

Electronic Ignition Sensor, aka the "Bean Can", Wires

Electronic Ignition Sensor, aka the “Bean Can”, Wires

Bean Can Wiring Plug Is Secured With A Wire Bail

Bean Can Wiring Plug Is Secured With A Wire Bail

Bean Can Plug Bail Removed

Bean Can Plug Bail Removed

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.

Remove Two Bean Can Allen Bolts

Remove Two Bean Can Allen Bolts

Bean Can Hardware Detail

Bean Can Hardware Detail

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.

Bean Can Ears Engage Camshaft

Bean Can Ears Engage Camshaft

Bean Can Large O-ring

Bean Can Large O-ring

Camshaft Coupling For Engaging Bean Can Ears

Camshaft Coupling For Engaging Bean Can Ears

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.

Inner Timing Cover After Engine Electrical Components Removed

Inner Timing Cover After Engine Electrical Components Removed

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