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The Bosch voltage regulators, both mechanical and electronic, in the metal cans, were the best. There is nothing wrong with the mechanical type for early bikes. In an emergency an old mechanical one might do OK in any airhead model. NOTE that the electronic ignition could miss-fire with a mechanical regulator. The mechanical regulators DO wear, mostly from their constant points arcing. Electronic regulators will substitute for the mechanical regulator on any airhead model. Besides the Bosch and Wehrle electronic regulators that BMW furnished, there are aftermarket regulators available, and numerous car types could be substituted.

The rest of this posting applies ONLY to the Bosch mechanical voltage regulator, as used from about 1970-1980. There is a similar outward appearing unit, the Bosch ELECTRONIC voltage regulator, in a somewhat shorter metal can. These were the best of the electronic voltage regulators. The information on servicing and adjusting in this posting does applies ONLY to the Bosch mechanical regulator.

STANDARD SYSTEM TEST:

This test is best done with a battery already fully charged, but can be done with a less than full charged battery.

Press the plug connector at the little tab that releases the plug from the regulator, and thus UNplug the regulator. In the PLUG, jumper D+ to Df, you should probably make up a very short, perhaps 4 inch long cable with male spade connectors for this, and keep them in your on-bike tool tray, in case the regulator ever failed. There is no problem determining which terminal is which. The ones across from each other are D+ and Df. Do NOT jumper the brown wire.

Start the engine, monitoring the voltage at the battery. Slowly increase the rpm. From about 1500 rpm, the alternator should begin to have some output. That output increases with rpm increase, and continues to increase until the alternator system furnishes power to the system, and begins battery charging, increasing to the alternator limits, assuming enough rpm. Since there is no regulating action in the circuit at this time, the alternator will try to charge the battery fully, and then try to grossly overcharge the battery, so do not let the motor run at high rpm for more than a couple or three minutes....there is really no need to.

***Read this ENTIRE posting before proceeding further. If you do not feel competent, do not play with the regulator.

Servicing the regulator:

1. REMOVE the regulator from the motorcycle. Remove the tape surrounding the can-to-base. Remove the top metal can cover, by prying gently, all around. Position the regulator such that you are looking at a longer side, and the mounting tab is AWAY from you, but at the bottom. That is, the two mounting holes are towards you.

You will see a paper wrapped, hundreds of turns coil, it has an iron core, with a bendable little tab attached at the top. This is really a solenoid, which, when energized enough, pulls downward the metal clapper. The clapper, that movable metal part that is above the solenoid, extends downward on the right side and also has a pair of contacts spot welded to it, one on each side. In other words, the clapper is L shaped. Sort of.

On each side of those paired contacts, is a mating contact, these mount, via brackets, into the base of the VR. To the left of the coil is a round item, about 5/16" in diameter, nearly an inch long, probably painted reddish brown, with a wire out each end. This device is a wire wound "choke". It is a special coil of wire, whose main purpose is to reduce some of the electrical arcing at the contacts.

On the underside of the base, is likely a small metal plate, protecting and hiding a couple of resistors. Leave this area alone.

****Saying all this slightly differently: At the TOP of the solenoid, as part of the iron core, there is a tab, that goes to the LEFT. It is THAT tab that is the VOLTAGE adjustment for the regulator. That small tab is bendable up and down...and only a SLIGHT change will make a LARGE voltage difference. That tab presses against a spring steel blade that is riveted to the clapper. The steel blade extends even farther to the right, and is then riveted to a sturdy mounting.

****For most folks, simply a slight contacts cleanup and a voltage adjustment by this clapper tab, is all that is necessary. It is the CLOSED side of the three points that is the 'produce electricity' operating side, but all three points should be clean and shiny.

****NOTE: supposedly some of these mechanical regulators were built with a voltage adjuster, on the underside of the unit. It would make adjustment easy...but, if irregularities are found, servicing the contacts may be necessary, as well as adjusting the tab for the correct voltage.

In the REGULATING mode, the clapper contact(s) vibrates between the other two contacts. In one position...the position of at-rest, engine off, un-energized condition, the left contacts are closed, and the alternator rotor gets its magnetizing energy (at key-on) via the GEN lamp circuit, through those contacts. In the slight to more than slight over-voltage condition, the RIGHT contacts close, reducing the rotor electrical input.

****Note: if the contacts are excessively worn, a new regulator is a good idea. I see no reason an electronic regulator could not be substituted, except that then the motorcycle is not 'original'.

Most failures or other problems of the mechanical regulator are due to dirty or pitted points. These are cleanable with a thin piece of non-slick paper with a solvent. If well pitted, one should use some sort of rather thin points files (I use 200 grit only if REALLY bad, then 300; if no so bad I start with 300, and finish with 400). Do this CAREFULLY, and SQUARELY, and not remove but the tiniest amount of metal. There are also thin bladed semi-flexible contact burnishing tools at many electronics shops, which come in these grit grades. Many points files are too thick to fit. One can use a narrow strip of fine grit SANDpaper, holding a light pressure and pulling the strip through gently. DON'T use emery or other types of materials, they may be so hard as to embed themselves in the metal, causing fast wear.

2. Adjustment of contact spacing is not a good idea. It will upset regulation. However, if considerable metal was removed from the points due to their badly pitted condition, or one has bent things, adjustment may be necessary. The points (contacts) are spaced for both mechanical AND mechanical/electrical reasons. This mechanical voltage regulator is more complicated in operation than it appears. The spacing between contacts, the alignment of the clapper, the temperature compensating metals....ETC.

3. Resetting the voltage is done by SLIGHTLY bending the SMALL metal tab at the end of the clapper. At room temperature, the voltage should be about 14.0, and higher if colder, lower if warmer. This means that if the engine is hot, and the voltage regulator is also quite warm from the heat rising from the motor, the voltage should be more like 13.7. Be sure to replace cover properly and tape it against ingress of water, etc.
**NOTE: if your battery is not in good condition, you should NOT try to adjust the voltage regulator, as some battery faults will mask any good adjustment attempts.

FULL PROCEDURE:

Most of you will never do the full procedure. However, I have set it down below. Assuming one has cleaned up the contacts smoothly and squarely, one can proceed as follows to do a FULL adjustment, rather than simply touching up the voltage. IF YOU HAVE MESSED WITH THE CONTACT SPACING, YOU CAN SIMPLY RESET THIS MECHANICALLY AS FOLLOWS, AND THEN BEND THE TAB FOR THE CORRECT VOLTAGE. IF THE VOLTAGE SEEMS CORRECT ON THE MOTORCYCLE, YOU CAN PROBABLY LEAVE WELL ENOUGH ALONE!

***The very anal lab-type adjustment is shown, for those so inclined. Again...you probably will not have any need to try this full procedure, and simply adjusting the tab after cleaning the points...or....resetting the distance measurements, and then setting the voltage tab...is likely good enough:

1. The distance from the solenoid iron core (flat shiny metal) to the clapper, should be perfectly parallel, by critical look-see with your #1 eyeball, when the clapper, at the top, is depressed with your finger, GENTLY, to its mechanical stop. The adjustment is the RIGHT contact bracket, that rises from the regulator base.

2. Release the finger pressure. The air gap at the clapper contact-to-RIGHT contact, should be .012". The adjustment is the LEFT contact bracket, that rises from the regulator base.

3. With the regulator mounted to the motorcycle, plugged in, no jumper in the plug obviously, and metal can still off:
Reset the voltage regulating point, as described, with the bendable clapper tab. Remember: a SMALL adjustment makes a big difference, and the battery MUST be in good condition and FULLY charged, and the rpm raised enough, long enough, to ensure the battery is reaching the full charge point after starting the engine....this will take only a minute or so with a previously fully charged battery.

4. If everything is working OK, reseal the can with fresh tape. Use the tape rather strongly, so it stretches somewhat....and makes a decent watertight seal from the can to the base.

5. Most folks will NOT have the necessary test equipment to allow the more rigorous laboratory type testing and adjusting of the regulator. You will need voltmeters, a variable output power supply, resistors, etc.

...the procedure is as follows:

6. Connect a variable D.C. supply (one that does NOT have a lot of A.C. hum riding on the D.C. output...in other words, it is filtered by a capacitor or otherwise), such that the positive (+) output connects to the regulator D+. Connect the negative (-) to regulator D-.

8. Connect a thousand ohm resistor...1/2 watt size or larger, from that unsoldered choke wire, to an accurate voltmeter (+), and the voltmeter (-) and the other end of that resistor, should be connected to D-.

9. Connect another of the same type of resistor from D+ to the junction of the voltmeter and the choke wire.

10. Connect another accurate voltmeter across the power supply output. You can use one voltmeter and switch its connections back and forth, but it is better to have two voltmeters...both fairly accurate.

11. Increase the voltage slowly until the left contacts JUST
closes.   That point is measurable by the choke voltage jumping suddenly to a value under 1 volt.   Note the supply voltage.

12. DEcrease the voltage until that same point JUST jumps to a
level above 12 volts. Again note the voltage at the power supply.

13. For normal touring usage, the desired condition is such that:

a. The voltage to close the right contacts is 14.7

b. The voltage to close the left contacts is 13.8

14. Adjust the tension tab so that the average of these two voltages is 14.3, plus or minus 0.1 volt. The average here means to add the two voltages, divide by 2.

15. Bend the adjustment bar a tiny amount and repeat the measurements until results are correct.

****For those doing a lot of commuting with short cycles of stop and go, it may help to reset things a bit higher. Note that with the following settings and longer touring, you might use up battery water faster. Those with sealed batteries may see less life on your battery. For commuting use:
Right contacts closure at 15.1; left at 14.3; the average value to be 14.7

16. Resolder the choke, replace the cover, replace the tape. Reinstall on the motorcycle.

17. Check the battery charging with a voltmeter, on a fully charged battery, using the engine at around 4000 or even 5000 rpm.

Revisions:

01-07-2003: clarify steps 8 and 9 regarding resistor connections
01-16-2003: formatting and minor wording
04-02-2003: Clarify Introduction and minor other clarifications.