Page 2 of 3 FirstFirst 1 2 3 LastLast
Results 16 to 30 of 42

Thread: Two different R27 problems!

  1. #16
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    20,663
    Quote Originally Posted by millerph View Post
    According to the shop manual, to get the bike started you either need juice in the battery or the ability to get it rolling quick enough to bump it, with the battery disconnected.
    I'm still having trouble grasping this. It's been my understanding that w/o a battery, the bike won't start. The ignition system on the R27 is not that different than my /7.

    However, after exchanging some thoughts with members on a German forum, it does sound like the bike can be started without a battery. However from what I can tell, you must get the engine spinning quite fast, well over 1K RPM and keep it there. If the RPMs drop, the bike will die.

    I think this relies on the residual magnetism in the armature. Without this and without sufficient engine speed, I think it would be nearly impossible to start and keep a bike running without a battery.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  2. #17
    Hi Kurt,

    That is basically what the shop manual says. To start it by bump starting you will need to have the engine spinning above 1800 rpm, if the generator is working well. That is supposedly the point where the generator is supplying more juice than the battery and the regulator lets the generator send the juice to the coil and the battery. Below that rpm the generator is putting out too little and the battery feeds the coil through the regulator.

    An interesting, simple idea that I'm glad is not on my newer bikes!

    Thanks for looking it up!

    Cheers,
    Paul

  3. #18
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    20,663
    I was directed to a section in my R25/2 repair manual for troubleshooting the dynamo. For one of the tests, it says to get the engine running at around 2500 rpm and turn on the head light. Then disconnect the battery ground. Removing the ground should result in slight brightening of the light and restoring the ground should slightly dim the light. I guess the test is to confirm that the generator is actually working.

    So, I guess the bike can run without the battery in the circuit. Starting it might be kind of sporty, but looks like it will run without the battery as long as the RPM is kept up.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #19
    Well, I put the new brushes in and thoroughly cleaned the commutator and all the connections inside the generator housing. The charging light got quite a bit dimmer, almost going out at full rpm. Checking the voltage I'm getting up to 6.4 V at the blue and red wires versus ground (DF and 61).

    So, while it is better, it is not good enough!

    I took the seat off so I can take the tank off without screwing up the seat (again). Next is to check the connections at the new voltage regulator. I think the problem is in the generator however as it really should be putting out closer to 7.4 instead of 6.4.

    Is there a way to test the armature? Any other thoughts?

    Cheers,
    Paul

  5. #20
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    20,663
    Paul -

    I don't recall...have you cleaned the armature, especially the slots between each set of contacts? I can't seem to find information on the R27 winding measurements. I would check the resistance between adjacent contacts...it should be fairly low. Also, each contact should be very high with respect to the iron core.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  6. #21
    Hi Kurt,

    I did a thorough cleaning such that it looks like Alan's picture. Good idea on the resistance checks, I will do that (fourth time taking out the field coil plate!).

    I also found on the 6V VW forum a check for the generator output. You basically disconnect the generator from the regulator and run the generator separately. Theoretically without the regulator it should read about 17V. It turns out that a bad regulator can keep the voltage too low by restricting the current. The VW forum showed a drawing of their Bosch regulator and it looks a lot like the R27's. They do mention that the electronic regulators may solve that problem as they can correct a wider range of voltage/current issues.

    Now that the seat is off I will lift the tank off to clean the regulator contacts first and check that wiring for continuity. Sounds like enough to keep my evenings busy this week!

    I will also get a chance to replace the aluminum trim around the seat.

    Thanks again for your help!

    Cheers,
    Paul

  7. #22
    Rally Rat
    Join Date
    Nov 2007
    Location
    In the state of Misery for now.
    Posts
    1,295
    In general terms, since I do not know R27

    The best way to test a generator is to run it as a motor. If a generator will not motor, it will not generate.

    To do this you need to apply 6V and ground to the case, and then you have the fields to excite. There are 3 common fields. A circuit, where the field connects to ground, B cir suit where the field connects to 6V and isolated, where you have to connect the fields outside. Polarity is critical.
    The generator with the fields connected will motor at a slow speed, if you remove the field connection it will briefly speed up then stop.

    The mechanical regulator can be changed with as little as a 1 foot drop. You have to let one run for 15 minutes with the cover on before checking the voltage, as these have bi metal strips and copper wire, all of which change with temp.

    Normally to adjust the voltage you bend the spring seat up or down to change the voltage.

    These time consuming steps are often omitted in today's hurried world.

    Rod

  8. #23
    Hi Rod,

    Neat idea! I will try to figure out how to do that!

    Cheers,
    Paul

  9. #24
    copandengr
    Join Date
    Aug 2010
    Location
    Marion, AR
    Posts
    115

    Generator testing

    The armature can easily be checked with an ohmmeter. Any given commutater segment should have continuity with the segment that is 180 degrees away. There should be no continuity between any segment and any other part of the armature, nor should there be any continuity between any segment and any other segment that is NOT 180 degrees away from the segment in question. There are only two possibilities with an armature winding as far as failure goes... They will either fail open, or in other words have a broken winding, or they will fail by shorting the winding or segment to the armature body

    Weak brush soprings will allow the brushes to bounce on the commutator and allow arcing. This is seen by the black streaks on the copper. An out of true armature will also cause the bouncing as will worn out bushings.

    Any good starter/ alternator/ generator shop can rewind an armature, or if needed repair the commutator. It might not be all that cheap to do, but depending on how scarce this generator is the cost could be justified.

    One last thing.... On a high mileage generator it is common to have a densely packed build-up of carbon between the segments of the commutator, and there can also be copper dust there also... either will short the segments out and cause failure... When a commutator is turned down during a rebuild, the insulating material between the segments must be undercut to inhibit the ability of copper buildup across the segments as well as preventing arcing bewteen segments during normal operation. Again, this is an easy thing to do for a properly equipped shop. The average Joe can do it by very carefully using a thin hacksaw blade.

  10. #25
    The entire armature/commutator is very clean and there is no grease or build ups. The gap between the commutator parts is clean and the insulation between the stainless parts of the armature is clean. The commutator is shiny copper.

    But, every one of the armature stainless plates has continuity to every other part. Also, every segment of the commutator has continuity to every other segment. There is no continuity between any of the commutator plates and any of the armature plates.

  11. #26
    Registered User
    Join Date
    Jan 2006
    Location
    Wisconsin and Florida
    Posts
    411

    Cooked Armature

    "11-19-2010, 08:18 AM
    - while riding down the freeway last night the red light came on. Over the next 15 miles home the lights got dimmer and dimmer and were barely lit for the last 5 miles. The bike ran fine otherwise. I've been having to add water to the battery most every time I ride it."

    Above sounds like generator was overcharging to the point the armature windings got hot enough internally to melt the lacquer or other coating on the windings and short them together resulting in the following:

    "03-06-2011, 06:46 PM
    every segment of the commutator has continuity to every other segment"

    This was a common occurance with Harley Sprint 1965-1972+- which was guaranteed to cook its generator with sustained interstate 70mph operation.
    The generator of the sprint is very like the generator in my R26 BMW and maybe same or very close to same Bosh armature

    A fellow I used to ride with who rode BMW R26 in the late 1960's would not sustain speed over 60mph for any length of time - not because of electrics - but because he swore it always would lead to conrod big end failure - he had rebuilt several times.

  12. #27
    Could be overcooking. I thought that would be controlled by the voltage regulator but after replacing it to no effect and after talking with Benchmarks and Motorad Electric it might be an internal armature short. Interestingly, on my last check I was getting 4.9-5 v consistently from the generator. As the voltage is a function of the current and the windings, a short in the windings would cause the lower voltage.

    Apparently a good test can be done with a growler, which I don't have. Bob's does however, so I took it over there today. We'll see!

    If it is a bad armature the options seem to be:
    new armature for $440
    new generator for $1063
    switch to a 12v system for $575

    Any opinions?!

    Thanks,
    Paul

  13. #28
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    20,663
    I would want to stay 6v but sometimes finances needs to be factored in.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  14. #29
    I think the only reason to keep it a 6v is originality. That might make a difference in resale value, but I doubt much. I'd go with 12v, but then I like triple disk brakes.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '18 Street Triple RS, 2020 R1250R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  15. #30
    Registered User
    Join Date
    Jan 2006
    Location
    Wisconsin and Florida
    Posts
    411
    "Could be overcooking. I thought that would be controlled by the voltage regulator but after replacing it to no effect .........."

    Quite likely bad regulator system at first produced the overcharge/overload which burnt the armature up before you replaced the regulator. If one of these old relecs was cranking out
    enough charge current to boil out the battery repeatedly it almost certainly toasted itself. I
    have never been blessed with such an excess of charge current on any vintage machine.

    If you have the person with a growler and he knows how to use it that will probably tell the tale.

    If the 12 volt system you mention is like the 200 watt alternator that is sold for /2 it is wonderful
    simple and easy to install and will run quality h4 light and electric vest. Expensive headlight
    reflector conversion though and if stand on the rear brake in traffic too long will melt tail light
    lense.

    When I was buying these armatures (bosh) for HD Sprints in the late 1960,s they were $35
    from a BMW dealer and $60 from a Harley dealer.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •