6volt generator-R27

[James.A]

This bike has been a rolling re-hab project for about 5 years and I still have a long way to go. Presently, I am having trouble getting my mind around the generator system. Having read the trouble shooting section of the factory manual several times, I have a few questions. If the system was not properly polarized when a new regulator was installed, can it be corrected now or is the system set in?

The bike will run with the battery negative wire pulled which to my mind indicates generator output, but the battery goes weak after a few short trips. It stranded me at a friends house last week. The battery was down a bit and it is difficult to start unless the battery is fully charged. Is this typical?

Any other thoughts on the topic?

[James.A]

This is a picture of the bike rigged up for generator testing with the motor running. It won't get a road test anytime soon.

[wuli959]

Pretty sure that these /2 type bikes will run fine on the generator without the battery being hooked up. I used to ride my R69S without a battery installed in the bike.

Here is a link to info on /2 electrical systems you may find helpful

[dbrick]

[QUOTE=wuli959;342496] Pretty sure that these /2 type bikes will run fine on the generator without the battery being hooked up. I used to ride my R69S without a battery installed in the bike. [QUOTE]

David's right. The ignition system (magneto, points, HT wire, spark plug) is completely separate from the rest of the electrical system (generator, regulator, battery, etc.). It may be intermittently difficult to start, but this is not related to the state of the electrical system...or it shouldn't be, unless a prior owner has tried to "upgrade" the system by bypassing the magneto.

So I think you have two challenges here: first is the intermittent hard starting. Magnetos and coils get weak as their insulation breaks down due to age and heat. I don't know how to diagnose them. If it turns out bad or weak, there are some guys in Europe who rebuild them, but I'd probably start locally with Vech at Bench Mark Works to see what he could do with it. The points could also be worn and/or misadjusted (and points wear could be due to a bum condenser), the HT wire could have hardened and cracked insulation (so the HT current escapes to ground before reaching the plug), and the plug connector could be cracked with the same result.

Second is the state of the electrical system. This is standard genereator stuff, again I can't help with particulars. If the generator is weak, you'll have an easier time finding repairs.

[20774]

R27s are battery ignition systems, not magneto ignition systems. They need the battery to run.

http://jeff.dean.home.att.net/r27.html

[dbrick]

Thanks for the correction. I was extrapolating from my R50/69/69S experience, and assumed that the singles from the same era were similarly designed.

[20774]

I would have thought the same thing, but I remember someone mentioned they were different...I had to recheck. I've just now looked at a Mobile Tradition book covering the bikes from 1923-1969. The first single, R39, in 1925-1927 was magneto ignition. All singles after that were battery ignition. I'm not sure I've read anywhere the reason for that, or the point was not well made. Maybe the magneto was too much of a mechanical drain on the engine...they needed as much power as they could find, so opted for one less heavy rotor.

But none of this helps the OP... I still can't get my head around "bike runs with battery negative pulled." Must be a separate ground somewhere to make things work.

What does the voltage across the battery terminals read when the bike is running?

[James.A]

I spent the better part of today kicking the darn thing. It came to me with a factory service manual that is translated in 4 languages, Some of the translation from German to English is less than concise in English. I have determined that the regulator is not regulating at the top end of the spectrum. 8.2v observed but the maximum allowed is 7.9v. It looks like the regulator is toast. To conduct all tests, I still need to acquire an Ammeter that zeros at center, and a variable load testing device. I have a battery load tester for 12v automotive, but I need to load the system to precisely 60 watts. There are 3 more "motor running" tests to attempt, but I really need those 2 devices to be confident in ordering parts.

There is a test called "no-load cut in test" but I am not sufficiently confident in todays result to report on it. On the upside, after spending the whole first week of my 2 weeks vacation on it, I am starting to get a feel for what I'm up against.

What I still wonder about is if the regulator was not correctly polarized, is it ruined?, or can I follow the recomended proceedure to set it right?

[20774]

I've not heard about "polarizing" a voltage regulator, certainly not on a /2 twin. Polarizing the coil on the magneto is a possibility, but that is part of the twin ignition system...that's different.

I'm not sure if the generator/regulator is the same as the twin. Here are a couple of links that describe the function of the twin generator.

http://www.geocities.com/MotorCity/S...13/dynamo.html

http://www.snafu.org/restore/uandm_bmw_v1.pdf

You might want to give Vech a call at Bench Mark Works.

[James.A]

Thanks for the links, Kurt. I tried calling Vech yesterday afternoon but ended up with the voice mail each time. The weather is beautiful here today so I might just go for a ride and give the garage a rest.

[James.A]

I've tried calling Vech and sent an e-mail. No response thus far. So far, I have determined that the generator is generating, (7.92v indicated by a digital Fluke instrument). Yet, the battery will drop to less than 6v when I take the bike out and run it. Given my incomplete understanding of the system, I'm thinking the generator is not correctly polarized. I have resorted to quizing the Harley/Indian/British guys locally. They all tell me that they know nothing of the Bosch 6v system and are of little help. My test results are that the generator does, in fact, work and that the cut-in function of the regulator seems to work as desinged. (the instant that the RPM's drop below the cut-in level, The bike quits running with the battery by-passed)The bike depletes the battery while running even thought the tests indicate generator output. I do not own or have access to equipment to go any further in diagnosing the fault. Based on my observations and testing of the last week and a half, I know that I don't know enough and I am struggling to figure it out. It might as well be a BSA. We must assume that the people who designed, assembled, and serviced these bikes are all dead and gone. We are truley "on our own".

[nhbmw]

R27s are battery ignition systems, not magneto ignition systems. They need the battery to run.

http://jeff.dean.home.att.net/r27.html

Had a '64 R-27 when it was about 4-5 years old. I was testing the points with a meter (ignition on) and pulled the movable point open with a fingertip, forgetting the engine was warm and the crank was just past TDC. The plug fired and the crank revolved about a revolution. The advance weights dragged my left index finger and mashed it into the ignition housing. That finger hurt for weeks. A magneto can't do that because the crank has to be revolving at significant speed for a mag to generate a spark.

Back in the early days of motoring, many cars had manual spark advance, and hand-crank starters. There was a clever "self-starting" trick, at least for warm engines. Ignition off, spark fully retarded, pull the crank handle to just past TDC on a power stroke. Then climb into the car, ignition on, and advance the spark timing all the way. That opened the points, and often started the engine, as I *almost* did with the Beemer.

[20774]

So far, I have determined that the generator is generating, (7.92v indicated by a digital Fluke instrument). Yet, the battery will drop to less than 6v when I take the bike out and run it. Given my incomplete understanding of the system, I'm thinking the generator is not correctly polarized.

One of the leads going to the battery is the positive lead from the generator. The other battery lead should go to ground. When the bike is running, what does you meter says is the voltage at the "+" lead from the generator relative to ground? If it says the 7.92v, then how can the battery be depleted? If there's voltage coming into the battery, it should fill up (using the old water-in-the-tank analogy). Is the negative ground cable OK...have you check it's resistance?

If the "+" lead gives you negative volts, then that might be something associated with polarization. I still don't understand this polarization question. If the generator is at all like the one on my /2, there is no polarization associated with it. There is a central rotor which is energized by the bike's system...I guess initially from the battery. It becomes a temporary magnet due to the current going through the internal windings. As the engine turns, that magnet comes near windings in the housing (or stator) of the generator. A magnet moving past a coil of wire produces current. This current is what is then sent to the battery for charging as well as used to charge the coil.

Is there a red charge light on the headlight shell? Does it function normally, like on bright red before engine start and goes off after you start the bike?

Have you checked in at the Yahoo /2 Mono club? I'm sure there are guys over there that could iron this out for you.

http://autos.groups.yahoo.com/group/bmw-mono-club/

[LOSTBOY]

Polarizing a generator (not the regulator) is something done when renewing the armature or converting from positive to negative ground (or vice-versa). A working generator does not need to be polarized.

You do have a problem with the regulator. 8 volts is about all one of these systems will put out with the generator full-fielded. Bob's and others sell a very good electronic reguator.

If the battery is fading after a few short runs, you may have a problem with a component failing after it gets hot. You may want to take it to a shop that has a "Growler", which effectively suurounds the armature in a magnetic field for testing.

Armature failure is a common problem in these bikes, and they are getting very expensive.

[James.A]

Thanks everyone. I had pretty much decided that I was over-thinking this and that it was time to start throwing money at it. It is helpful to know that an inproved regulator is available. Does anyone know if a 12v conversion is available for these singles? Also considering a voltmeter clamped on to the handle bars to monitor battery voltage while running.