Page 10 – Airheads Beemer Club

Spark Plug Caps

On the early Airhead points type models, spark plug caps contained a resistor of 1000 or 1200 ohms. Using a resistor inside the caps is a better method than using highly variable (between manufacturer’s especially) “resistor” type spark plugs, in which some of those resistors were actually coils. The resistance caps reduced Radio Frequency Interference, and helped form the proper type of electrical spark itself. Later Airhead points models and all electronic ignition models used 5000 ohm caps for even lower RFI, with added safety benefit for the 1981+ electronics ignition…described later here.

The spark plug cap resistance has more than one purpose:
It reduces spark plug tip and ground electrode erosion, and therefore greatly reduces any gap change over the life of the spark plug, and does this by reducing the electrical current flow. It does NOT reduce the applied voltage. Reduces some types of radio interference. Works in a complicated electrical way with the coil to produce a quality spark at the spark plug for good fuel mixture igniting. There are some other beneficial and rather complicated effects as well. Note that if the resistance is too large a value, then the EFFECTIVE spark ENERGY (combined voltage, current, and with SOME time effect) will be lessened too much, and, this means that using resistor spark plugs WITH resistor caps is a BAD IDEA.

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Servicing a Valeo Starter

The chances are very good that your starter problem is relatively cheap and easy to fix. Perhaps your starter has the same symptoms as stated below. If not, you can still check things out with the part marked “Testing”, and once a problem is isolated, the remaining portion covers disassembly and re-assembly of the Valeo.

Reviewing the symptoms: The starter operates correctly most of the time. When the starter does operate, the engine is cranked over at a reasonable speed and it does not appear that the starter motor is struggling as if the battery is nearly dead. When it does fail, you still hear a clicking noise, every time you press the starter switch. This clicking noise is a rather strong sound from under the starter cavity cover (not to be confused with a small clicking noise which is the starter relay). Most of the time, when it is failing, several successive starting attempts will get the starter motor to eventually operate.

If the above wordy sequence is true, your problem most likely has to do with the starter solenoid (rides piggyback on the starter motor).

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Making the Bosch (and Wehrle) Metal Can Electronic Voltage Regulators Adjustable.

I wrote this article because a few people asked for it. You can purchase an adjustable voltage regulator quite reasonably from http://www.RockyPointCycle.com or http://euromotoelectrics.com. But, the stock metal can regulators are not difficult to modify, the cost is very low, and you get to keep the original stock appearance …if you want-to. The metal-can VR’s are very reliable ….and are relatively easy to repair. They can even be modified to work with very high powered alternators for the Airheads (by changing the power transistor inside). These metal can regulators, no matter the name on them, MIGHT have been made by Bosch or Wehrle.

The exact same procedure is involved….(and the same hole drilling and adding a grommet, if you want to). Here is a photo of the Wehrle METAL CAN Electronic Regulator, with the potentiometer, with factory sealing paint. This is a how-to article, the purpose is to make your Bosch or Wehrle ELECTRONIC metal can unit easily adjustable. This article is NOT for the similar (but taller) metal can mechanical Bosch regulator…see http://bmwmotorcycletech.info/boschmechreg.htm.

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Ignition Systems; historical & modern

The following article is a SIMPLIFIED explanation of ignition systems, although lengthy. There is CONSIDERABLY MORE technical information, including repairs, etc., in the author’s website, particularly here:
http://bmwmotorcycletech.info/ignition.htm

A common type of ignition in very early cars consisted, typically, of wooden boxes, with a vibrating electrical contact which sent battery energy into a coil of a modest number of turns of wire wound on an iron core located inside the box. There was another coil of wire wound on that iron core, with thousands of turns, and these turns ‘transformed’ the lower voltage of the ‘primary winding’, fed by the battery, to a few thousand volts, and this was applied to the spark plugs. In most early engines the spark was applied continuously. Somewhat later a rotating switch was used. It had a contact or close by contact, one for each cylinder, and this was called a ‘distributor’. The only problem with the vibrating contact system is that the spark output can not be set to ‘fire’ the spark plug at a very specific piston position, although the distributor method helped SLIGHTLY. With the very low compression ratio and very low power output of these engines, together with the very long stroke and large diameter pistons, these ignition methods worked OK. As engines improved in various areas, the need for better and more precise ignition came about.

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GEN Lamp Failures, Resistor Modification

The GEN lamp supplies a very small initial current to the alternator rotor to enable the alternator output & charging process to begin as soon as modest rpm is had. If the lamp burns out, the alternator may not provide any output. This article describes the system and a popular modification which eliminates any lack of charging from lamp burnout (which is actually fairly rare).

General comments about ‘modifications’:

As a general rule, ‘The factory knows best’ is a fairly accurate statement. However, few of us have UNmodified motorcycles. Our bikes are a reflection of our personal statements and desires; and, are thus often modified for many reasons. I am NOT in favor of many of the modifications that we all see. Some of these modifications, which I have done myself, are not very economical…or…do less than is often believed. Some modifications can REDUCE reliability.

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Dyna III Electronic Ignition Troubleshooting Guide

This didn’t seem to be on their website anywhere, but it is the troubleshooting guide they distribute with new DYNA III kits. So if you inherited a bike that already had a DYNA III kit (that thing that doesn’t look like points) you may need to reference this. These units are pretty rock solid, but occasionally they do go. Usually the electronic module is the thing to go, but occasionally the sensor plate will go. The reason for that is these bikes were designed wonderfully to keep water in the ignition area. If water sits in there for too long it can destroy the sensor plate. Drilling a small hole in the bottom of the case is one solution.

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Dual Plugging

I responded to some questions on and off the Airheads Mailing LIST about dual plugging and the automatic advance unit (ATU). I commented on setting timing and the types of modifications made by others to the ATU. Although I have had dual plugging on one of my R100RT bikes, and have had it on others, I did not think it necessarily always warranted for the average rider.
The result was a lot of misapplied and mistaken comments from Members of the Airheads LIST. I got other interesting replies, to say the least, almost all being off the list.

HERE, I will try to make some definitive comments on dual-plugging and the automatic advance units. FIRSTLY, I advise you to read the more comprehensive and likely more-up-to-date article on dual plugging on my website:
http://bmwmotorcycletech.info/dualplugging.htm

In my estimation, dual plugging is, or can be …an minimal to moderately expensive solution to some things that might be …or ARE ….problems.

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Diode Boards & Grounding Wires (including information on testing diodes)

Diode boards generally fail by having one or more diodes ‘open’ internally, “open’ means they do not exist electrically. Rarely do they short-circuit. There are small diodes on the diode board with two types of functions. Early boards, such as on the /5, did not have as many diodes as later boards, the later boards had a stator windings center-tap, which used the extra diodes to improve output wattage. Failure of any of the small diodes will cause strange output problems. Usually, a diode board failure is at the solder joint of one or more of the six large power diodes; or, that diode opens. It is quite rare to see shorted large diodes on the board. If a large diode solder joint becomes lousy or opens or the diode itself opens, the alternator will still produce current, but it will be quite considerably lower in total wattage output. The typical result of one large diode opening (or, solder joint failure) is that the battery will show near proper voltage during riding, but when the headlight is turned-on, the voltage will sag rather considerably.

Diode board testing and information about repairing the faulty Wehrle-manufactured ones (I’ve seen a few Bosch boards with the same problems with non-bent-over large diode leads and soldering failures) is covered in depth in the June 1999 issue of AIRMAIL, an article by the late great BMW Guru Oak Okleshen. Airhead owners may want to read the article. The Oak-recommended & difficult to do board modification could be done, with considerable effort, for reasons of solder joint failures, more likely if you have a R100 engine, which develops more heat (worse if an RS or RT). I’ve had good luck with a much simpler method, which is the removing of the ‘paint’ with gel type paint remover (often it has no effect though and abrasion is needed). I always enlarge the solder pad area first, whether the gel remover works or not, by careful scraping with a sharp Xacto thin blade hobbyist knife (don’t remove copper material), & then re-soldering using a high temperature solder (50-50 plumber’s solder and rosin flux) and a extra hot soldering iron. No re-painting or re-coating is needed, but certainly could be done. My repair method is vastly easier to do because drilling the PC board & adding wires & soldering per Oak’s method is quite difficult & best done by total disassembly, which Oak did not get into and is a huge PIA! Yes, it can be done with long tweezers or forceps, but that is quite tricky. I cannot recommend Oak’s method, and I won’t even do it myself. I’ve also seen several Bosch branded boards with this problem, perhaps Wehrle made them? There have been some other Bosch and Wehrle labeled products that made me think either could have manufactured them.

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Diode Boards & Charging

Many are intimidated by electricity, and the amount of electrical problems with Airheads can be a sore point. Most often problems are due to lack of regular maintenance, particularly cleaning and tightening various connections, checking alternator brushes, changing the battery before a catastrophic battery failure; and general old age and mileage. This is really not much different from other motorcycles. If properly maintained, the Airheads electrical system works fine and is reliable. If, however, the bike is ridden mostly in stop and go city traffic, the charging system may not keep up, and the battery might require nightly re-charging. The Smart type of chargers are especially convenient for that purpose.

The stock charging system starts producing usable amounts of electricity at ~2000 rpm, but upwards of 4000 rpm may be required for enough output to take care of lights (including extra lighting), ignition, heated clothing, accessories, and have electricity left-over for re-charging the battery. Aftermarket alternators of higher output are available that fit inside the timing chest area.

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Bosch Metal Can Mechanical Voltage Regulator, Cleaning & Adjusting

The first part of this article covers the basics for this 12 volt VR unit, as used on BMW Airhead motorcycles before BMW changed to electronic ignition in 1981. This article applies ONLY to the mechanical voltage regulators. These were used on the Airheads from 1970 to ~1980.

At the end of this article are some addendums. #1 is a description and schematic diagram. #2 is for the BMW /2 (6 volt) motorcycle’s VR. I suggest you DO read that section, even if you do not have a /2, as it has a slightly different way of explaining the servicing (included in this article).

Voltage regulators, both mechanical & electronic, in metal cans, were installed as stock items on early BMW Airhead motorcycles. There is nothing wrong with the mechanical type for the early BMW Airhead Motorcycles, except that mechanical types DO wear, over time & mileage. In an emergency an old mechanical VR might do OK in any Airhead model, although the electronic ignition could possibly (not necessarily will) miss-fire occasionaly with a mechanical regulator. Mechanical regulators wear mostly from their constant points vibrating/buzzing/arcing. Electronic regulators will substitute for the mechanical regulator on any Airhead model, directly, with no problems. All the mechanical regulators were inside of tall metal cans. Later voltage regulators were electronic; but the early electronics versions ALSO were in metal cans, but they were shorter in height. The next series were in smallish plastic cases, often with black bodies and red tops. There are aftermarket electronic regulators available, some are adjustable, & most 3 male spades type of voltage regulators from European cars (that the Airhead cable plug fits into) could also be substituted. The stock METAL can electronic regulators are also adjustable, there is an article on this Airheads website about how to go about that, since the adjustment is sealed. There is also a bit more of an article here: http://bmwmotorcycletech.info/boschelreg.htm

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