12 BMW 1983 R100RS Remove Diode Board, Alternator & Electronic Ignition Sensor

I want to update the charging system (upgrade the alternator and diode board to 400 watts), clean and lube the ignition sensor (aka, electronic points) advance unit and replace the hall sensors. I also want to replace the timing chain, timing chain tensioner and crankshaft sprocket and nose bearing. And I’m going to remove the crankshaft to inspect the main bearings.

To do all that I first need to remove all the engine electrical components inside the front engine cover, the diode board, alternator, ignition sensor (aka, the “bean can”, aka, the “electronic points”).

Diode Board, Alternator, Ignition Sensor Live Under Front Engine Cover

Diode Board, Alternator, Ignition Sensor Live Under Front Engine Cover

Although my engine is out of the frame, you can remove these electrical components with the engine in the frame.

Tools

I use a special hardened bolt to remove the alternator rotor from the crankshaft. I acquired this one from Euro MotoElectrics

Hardened Rotor Removal Bolt

Hardened Rotor Removal Bolt

I use an oil filter wrench to keep the rotor from turning as I remove the alternator rotor bolt.

Oil Filter Wrench For Removing Alternator Rotor

Oil Filter Wrench For Removing Alternator Rotor

Video

I shot a short video summary of how I do this work that you can see here.

Remove Engine Covers

DANGER
You need to remove the (-) battery ground cable BEFORE you remove the front engine cover. The cover can touch the diode board frame which has power applied to it. If the cover touches the frame of the board, it will likely short out the board and you get to buy another one.

I remove the front engine cover by removing the two Allan head bolts that secure it to the engine block to expose the electrical components.

Remove Front Engine Cover

Remove Front Engine Cover

Front Engine Cover Bolt Detail

Front Engine Cover Bolt Detail

Front Engine Cover Casting Mark

Front Engine Cover Casting Mark

Underneath The Front Engine Cover

Underneath The Front Engine Cover

I also remove the top engine cover so I can easily access electrical connections on the starter solenoid where some of the wires from the front engine components go.

Remove Front Engine Cover

Remove Front Engine Cover

Top Engine Cover Bolt Detail

Top Engine Cover Bolt Detail

Top Engine Cover Removed

Top Engine Cover Removed

Starter Motor Underneath Top Engine Cover-Starter Solenoid At Top

Underneath The Top Engine Cover-Starter Motor at Bottom and Starter Solenoid At Top

Engine Wiring Sub-harnesses

There are three wiring sub-harnesses/cables that connect to the components under the front engine cover and to the starter motor solenoid on the top of the engine. They exit the top of the inner timing cover as shown below through rubber grommets.

Wiring Harnesses That Connect To Front Engine Electrical Components

Wiring Sub-Harnesses That Connect To Electrical Components Under Front Engine Cover

From left to right in the picture above:

  • Voltage Regulator Sub-harness
  • Battery (+) Cable
  • Ignition Control Unit Sub-harness

Voltage Regulator Sub-harness

This sub-harness has at “T” shaped plug that plugs into the bottom of the voltage regulator on the right side of the frame spine tube.

Voltage Regulator Cable Plug Detail with "T" Connector

Voltage Regulator Cable Plug Detail with “T” Connector

The “T” plug has two BLUE wires on one terminal, with BLACK and a BROWN wire on the other terminals. One BLUE wire is from the generator lamp on the instrument cluster that carries a small DC current to energize the alternator rotor coils so they are magnetized before starting the engine. The other BLUE wire carries the DC output voltage from the diode board to the voltage regulator which is used to regulate the charging voltage to the battery. The BLACK wire sends power from the voltage regulator to the alternator brushes via the (DF) brush terminal and the BROWN wire is the ground for the voltage regulator via the (D-) brush terminal.

Battery (+) Terminal Cable

This cable connects to the large screw terminal on the front of the starter motor solenoid. It also includes a RED wire that plugs into the starter relay socket. The starter relay plugs into that socket mounted on the left side of the bike next to the frame spine tube.

Battery (+) Cable Detail

Battery (+) Cable Detail

Since the starter solenoid sends current to the starter motor, which pulls a lot of current, the starter solenoid is directly connected to the battery. All the current draw of the starter motor flows through the threaded terminal on the starter solenoid.

There is another wire that connects to the starter solenoid threaded terminal that comes from the diode board output terminal. Since that wire and the battery (+) terminal are connected together, the DC power output from the diode board goes directly to the battery to charge it.

Ignition Control Unit Sub-harness

This sub-harness has a special connector plug that attaches to the ignition control unit that mounts on top of the front brake line manifold on top of the frame spine tube.

Ignition Control Unit Cable Plug Detail

Ignition Control Unit Sub-harness Cable Special Connector Plug Detail

Ignition Control Module with Connector On Top of Front Brake Manifold

Ignition Control Unit Mounted On Top of Front Brake Manifold Showing Special Connector Plug

There is another white connector on this sub-harness the connects to the coils. It has three wires: GREENBlue, BLACK and BROWN.

Ignition Coil Plug: GREEN/Blue Power To Coils, BLACK Ground Path From Coils, BROWN Ignition Control Module Ground

White Ignition Coil Plug: GREEN/Blue Power To Coils, BLACK Ground Path From Coils, BROWN Ignition Control Unit Ground

The GREENBlue wire sends power to the coils. The BLACK wire is the ground path for the coils but it first goes to the ignition control unit. The ignition control unit opens the ground path when the spark plugs need to fire. The BROWN wire is the ground wire for the ignition control unit and the coils.

The other leg coming from the special connector plug has three wires that go to the ignition sensor inside the front engine cover. This is also called the “bean can” or the “electronic points.” There are two hall sensors inside the ignition senor, each with it’s own wire, and a common ground wire.

Since the ignition sensor is connected to the camshaft which turns at a half-turn for every full turn of the crankshaft, each hall sensor is 180 degrees from the other so one of them fires every half revolution of the camshaft which is every full revolution of the crankshaft. Both of the spark plugs fires every full revolution of the crankshaft. One of them does nothing since the valves are open and it’s piston is not on the compression stroke. Therefore BMW airhead bikes use what is called a wasted spark ignition system.

Remove Diode Board

The diode board is secured to the inner timing cover with locking nuts and washers on four studs.

Diode Board Mounts To Inner Timing Cover on Four Studs

Diode Board Mounts To Inner Timing Cover on Four Studs

NOTE:
BMW originally installed rubber mounts for the diode board. They were chasing diode board failures, but the cause was not vibration. The rubber mounts are a bad idea as they fail in time and then the diode board can fall into the front cover shorting it out. When I first got this bike in 2015, I replaced the original rubber mounts (two were failing) with solid mounts.  You can see how I did that work here.

–> 12 BMW 1983 R100RS Check Diode Board, Replace Rubber Mounts

After I remove the nuts and washers, I pull the diode board off the studs. Then I remove the wire on the left side that comes from the alternator “Y” (center tap) terminal, and the wire on the right side that is the DC output from the diode board that goes to the solenoid threaded terminal to charge the battery.

Remove Diode Board Locking Nuts

Remove Diode Board Locking Nuts

Alternator "Y" (Center Tap) Terminal Goes On Left Side of Diode Board

Alternator “Y” (Center Tap) Terminal Goes On Left Side of Diode Board

Diode Board DC Output Terminal On Right (Both Terminals Are The Same)

Diode Board DC Output Terminal On Right (Both Terminals Are The Same)

Remove Wires On Back of Diode Board

There are two connections on the back of the diode board. One is a wide plug with three large wires from the alternator stator cover. Each wire carries one of the three phases of AC power produced by the alternator. The other is a female spade terminal with a blue wire that that has DC power and goes to the voltage regulator.

Back of Diode Board Wiring Connections

Back of Diode Board Showing Wiring Connections

NOTE:
The regulator measures the voltage produced by the diode board using the voltage on this blue wire. If the voltage from the diode board reaches 14.3 volts DC, the voltage regulator shuts off current flow through the alternator’s rotor and when the voltage drops low enough, the regulator again allows current to flow through the rotor. By adjusting the time no current flows through the rotor, the voltage regulator prevents overcharging the battery.

I remove the three wire plug and the blue wire connector from the back of the diode board.

Alternator 3-Phase AC Output Terminals (Plug Can Go Either Way)

Alternator 3-Phase AC Output Terminals (Plug Can Go Either Way)

Voltage Regulator Blue Wire Can Go On Either Vertical or Horizontal Terminals

Voltage Regulator Blue Wire Can Go On Either Vertical or Horizontal Terminals

I remove the other end of the “Y” wire from the terminal on the alternator stator cover.

Alternator "Y" (Center Tap) Wire Removed

Alternator “Y” (Center Tap) Wire Removed

Remove Diode Board DC Output Wire and Battery (+) Cable

I remove the Diode DC output wire from the starter solenoid screw terminal. I remove the nut and washer, then the battery (+) terminal. Notice that the diode board DC output wire spade terminal is bent 90 degrees. This is necessary as there is very little space available for the wires due to the proximity of the crankcase breather valve and hose.

Solenoid Screw Terminal Detail with Battery (+) and Diode Board DC Output Wires

Solenoid Screw Terminal Detail with Battery (+) and Diode Board DC Output Wires

Solenoid Screw Terminal Hardware Detail

Solenoid Screw Terminal Hardware Detail

Battery (+) Terminal Removed

Battery (+) Terminal Removed

Diode Board DC Output Wire Ring Terminal Detail-Note 90 Degree Bend

Diode Board DC Output Wire Ring Terminal Detail-Note 90 Degree Bend

Diode Board DC Output Wire Removed

Diode Board DC Output Wire Removed

Remove Alternator

The stator cover of the alternator has a number of wires attached to it. Each of them has a terminal identifier that matches the wiring diagram.

Stator Cover Wiring Detail

Stator Cover Wiring Detail

Stator Cover Terminal Markings

Starting at the lower left is the “Y” terminal. This is the center tap of the alternator coils. The wire attached to it goes to the terminal on the left side of the diode board.

Stator Cover "Y" Terminal From Stator Coils Center Tap

Stator Cover “Y” Terminal From Stator Coils Center Tap

The brush terminals are next with one the (D-) and the other the (DF) terminal. These connect to the voltage regulator sub-harness. The (D-) is the ground path for the brushes and the voltage regulator. The stator cover creates a ground path back to the battery (-) terminal via the engine block. The (DF) is the power input to the brushes from the voltage regulator. Consequently, this terminal is insulated from the stator cover with fiber washers and a fiber sleeve that fits around the terminal screw.

Stator Cover "D-" Terminal Is Brush Ground Path Back to Voltage Regulator

Stator Cover “D-” Terminal Is Brush Ground Path Back to Voltage Regulator

Stator Cover "DF" Terminal Brings Power to Brushes-Note Red Insulating Washer

Stator Cover “DF” Terminal Brings Power to Brushes-Note Red Insulating Washer

At the lower right are three wires going to an insulator with three spade terminals. Each of these wires comes from one of the three alternator phases. Interestingly, a (D-) is shown next to the insulator, but the phase wires are called “U”, “V” and “W” which is cast into the insulator next to the terminals.

Stator Cover "D-" Next To The Three Phase Wires From The Stator Coils (The "W" Mark Is Just Visible On Top Insulator Terminal)

Stator Cover “D-” Next To The Three Phase Wires From The Stator Coils (The “W” Mark Is Just Visible On Top Insulator Terminal)

Stator Phases "U", "V" and "W" Are Marked On Insulated Terminal Strip

Alternator Phases “U”, “V” and “W” Are Marked On Insulated Terminal Strip

I am not sure why the stator cover has the (D-) cast into it at this location. But one thought is it signifies that the stator cover is a ground path back to the battery (-) terminal. That said, I find putting that mark next to where the stator phase wires go to the insulated terminal strip can lead to confusion as the (D-) marking shown on the wiring diagram applies to the brush terminal that is directly connected to the stator cover.

Remove Alternator 3-Phase AC Output Cable

I remove the three stator wires from the terminals on the stator cover and pull out the 3-phase output cable that plugs into the back of the diode board.

Alternator 3-Phase AC Output Cable

Alternator 3-Phase AC Output Cable

Remove Voltage Regulator Sub-harness

I remove the BROWN and BLACK wires that connect to the brush terminals. These wires are included in the voltage regulator sub-harness.

Brush Wires Included in Voltage Regulator Sub-harness

Brush Wires Included in Voltage Regulator Sub-harness

There is also a BLACK wire in the voltage regulator sub-harness that goes behind the inner timing cover to a spade terminal on the starter solenoid. It carries power from the starter relay to the relay inside the starter solenoid which latches the starter solenoid closed to apply battery power to the starter motor through the screw terminal on the other side of the starter solenoid.

Starter Relay Output Plugs Into Solenoid Terminal

Starter Relay Output Plugs Into Solenoid Terminal

Solenoid Terminals: (L) Battery (+) & Diode Board DC Output, (R) Starter Relay Power to Solenoid

Solenoid Terminals: (L) Screw Terminal with Battery (+) & Diode Board DC Output, (R) Spade Terminal Sending Starter Relay Power to the Starter Solenoid Relay

Voltage Regulator Sub-harness Removed

Voltage Regulator Sub-harness Removed

Remove Ignition Control Unit Sub-harness

The ignition control unit connects to the ignition sensor, aka, the “bean can”, which is mounted at the bottom of the inner timing cover under the alternator, via the ignition control unit sub-harness. I removed the upper plug of the sub-harness that connects to the ignition control unit and disconnected the white plug that goes to the coils when I removed the electrical system and the brake system. You can see how I did that here:

The sub harness connects to the cable from the ignition sensor using a special connector above the alternator. One half of the connector is black which is part of the ignition control unit sub-harness and the other half of the connector is brownish-yellow going to the ignition sensor.

Ignition Control Unit Sub-harness Connector to Ignition Sensor Unit

Connector Between Ignition Control Unit Sub-harness Connector And Ignition Sensor

Ignition Sensor Cable Enters Via Special Gasket In Side of Bean Can

Ignition Sensor Cable Enters Via Special Gasket In The Side of The Bean Can

The two halves are held together with a wire bale. I use a small screw driver to pull the bail out of the slot it sits in. It’s a bit fiddly to get the second leg of the bale off as it sits under the connector, but with some patience I get it out without mangling it.

Ignition Control Unit Sub-harness Connector Detail

Ignition Control Unit Sub-harness Connector Detail

Remove Bail Securing Ignition Sensor Plug with Small Screw Driver

Remove The Bail Securing The Connector Halves with A Small Screw Driver

Ignition Sensor Plug Detail

Ignition Sensor Plug Detail

Here are some details about the black connector on the ignition control unit sub-harness that the wire bale fits into.

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Ignition Control Unit Sub-harness Ignition Sensor Plug Detail

Then I pull out the ignition control unit sub-harness and the battery (+) cable from the top of the inner timing cover. They go through the same grommet so I remove them together.

Ignition Control Unit Sub-harness & (+) Battery Cable Bundle

Ignition Control Unit Sub-harness & (+) Battery Cable Bundle

Ignition Control Unit Sub-harness & (+) Battery Cable Bundle Grommet

Ignition Control Unit Sub-harness & (+) Battery Cable Bundle Grommet

Remove Stator and Housing

The stator is attached to the inner timing cover with three Allan bolts at 11:00, 3:00 and 7:00 o’clock.

Stator Attaches with 3 Allan Bolts

Stator Attaches with 3 Allan Bolts

Remove Stator Allan Bolts

Remove Stator Allan Bolts

Then I remove the coil springs that push the brushes down onto the rotor slip rings. I use a small screw driver to pull the foot of the spring up and out of the brush holder.

Remove Brush Coil Spring Before Removing Stator Cover and Stator

Remove Brush Coil Spring Before Removing Stator Cover and Stator

The stator has a steel ring that surrounds the stator coils. It is machined at the back to fit inside three large tabs cast into the inner timing cover. I put my fingers into the holes between the tabs and carefully pull the stator straight out. I don’t want to nick the stator wires as they slide past the rotor.

Stator Cover & Stator Steel Sleeve Fit Into Large Tabs-Note Stator Coils Behind Sleeve

Stator Cover & Stator Steel Sleeve Fit Into Large Tabs-Note Stator Coils Behind Sleeve

The stator has a sticker on the side with the Bosch part number. The last three digits “005” indicate this is a 280 watt alternator with the machined part of the steel sleeve sized at 107 mm to fit into an inner timing cover sized for the 107 mm stator sleeve.

Bosch Alternator Model-"005" Is 280 Watt with 107 mm Steel Sleeve

Bosch Alternator Model-“005” Is 280 Watt with a 107 mm Lip In The Steel Sleeve

Remove Rotor

The rotor is attached to the crankshaft nose with an Allan bolt. I use a socket to remove the bolt. To prevent the rotor and crankshaft from turning, I clamp the rotor steel fingers with an oil filter wrench as I loosen the bolt.

Alternator Rotor Attaches to Crankshaft Nose-Note Copper Slip Rings Brushes Run On

Alternator Rotor Attaches to Crankshaft Nose-Note Copper Slip Rings The Brushes Run On

Oil Filter Wrench To Keep Rotor & Crankshaft From Turning

Oil Filter Wrench To Keep Rotor & Crankshaft From Turning

Remove Rotor Bolt While Clamping Rotor Steel Fingers In Oil Filter Wrench

Remove Rotor Bolt While Clamping Rotor Steel Fingers In Oil Filter Wrench

Once I get the bolt loose, I unscrew it. It will unscrew out of the threaded hole in the crankshaft nose and then become free, but you can’t remove it. There is a second set of threads inside the rotor, so pull it out until it stops and continue to unscrew the bolt until it comes out of the rotor.

Although you would think you can now remove the rotor, you can’t. It has a taper that matches a machined taper on the crankshaft nose. This creates a very tight interference fit that prevents the rotor from spinning on the crankshaft. The rotor bolt applies pressure to the tapers, but the fit is tight enough after you remove the rotor bolt that you need a special hardened extractor bolt to remove the rotor from the crankshaft nose. I got this one from Euro MotoElectrics.

Hardened Rotor Removal Bolt

Hardened Rotor Removal Bolt

WARNING
This bolt MUST be hardened. If you use one that isn’t, the end of the bolt can mushroom under the force needed to pop the rotor off the crankshaft nose. It that happens, you have a real problem on your hands as the rotor is now stuck very tightly to the crankshaft nose.

The bolt screws into the threads in the rotor and I screw it in all the way in until it stops. Then I use the oil filter wrench to keep the rotor and crankshaft from turning while I tighten the extractor bolt until it pops off the crankshaft.

Hardened Rotor Removal Bolt Threads Into Crankshaft Nose

Hardened Rotor Removal Bolt Threads Into Rotor Threads And Pushes On Crankshaft Nose

WARNING:
The rotor is heavy and you don’t want to drop it when it pops off the crankshaft. Since it is clamped in the oil filter wrench mine is safe. But if you have the engine in the frame and put the transmission in gear to keep the crankshaft from rotating while you remove the rotor, hang on to the rotor with your other hand as you tighten the extractor bolt so it doesn’t fall on the floor.

You can see the taper on the crankshaft and the taper inside the rotor.

Crankshaft Nose is Tapered

Crankshaft Nose is Tapered

Rotor Has a Tapered Hole

Rotor Has a Tapered Hole

Rotor With Mounting Bolt

Rotor With Mounting Bolt

Remove Ignition Sensor, aka The “Bean Can”

The ignition sensor, aka, the “Bean Can”, is the bottom component inside the front engine cover. It is secured with two Allan bolts on either side. It has a cable with a special connector that plugs into the ignition control unit sub-harness which I removed earlier. I remove the bolts and pull the bean can out of the hole in the inner timing cover.

Remove Ignition Sensor Allan Bolts

Remove Ignition Sensor Allan Bolts

Ignition Sensor Mounting Hardware Detail

Ignition Sensor Mounting Hardware Detail

Ignition Sensor (aka "Bean Can") Removed

Ignition Sensor (aka “Bean Can”) Removed

The base of the ignition sensor has an o-ring to prevent engine oil from leaking. If you see oil under the ignition sensor, this o-ring has failed.

Ignition Sensor O-Ring Keeps Oil From Leaking

The ignition sensor has a pinned shaft that engages with a coupling on the end of the camshaft to spin a magnet past the two Hall effect sensors that act as the points. Here are two references about how Hall effect senors work and how they are used.

The Hall effect senors generate a voltage as the magnet goes by which is sensed by the ignition control unit. It turns off the current flowing through one of the two coils of wire inside each ignition coil. Inside each of the two coils, the collapsing magnetic field in one coil of wire creates a large current in the second coil of wire that is connected to the spark plug wire causing the plug to fire.

Ignition Sensor Alignment Pins Fit Into Camshaft Coupling

Ignition Sensor Alignment Pins Fit Into Camshaft Coupling

Camshaft Coupling Slot Connects with Ignition Sensor Pins

Camshaft Coupling Slot Connects with Ignition Sensor Pins

Here is what the front of the engine looks like now.

All Gone :-)

All Gone 🙂

2 thoughts on “12 BMW 1983 R100RS Remove Diode Board, Alternator & Electronic Ignition Sensor

    • Hi Steve,

      Thank you. I felt this one got a bit long, if not too long, because I yielded to the temptation to talk more about the wiring in the sub-harnesses than just showing how to remove the components. I try to keep my videos no longer than about 10 mins, so this one was well outside that goal. I plan to keep to my rule of no more than 10 mins +/- in the future.

      Best.
      Brook.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.