The Airheads Beemer Club is a non-profit club reclaiming the 'Legendary Motorcycles of Germany'

Topic-icon 1974 R75/6 Charging problems

  • Doodah
  • Doodah's Avatar Topic Author
  • Offline
  • R100 Level
  • R100 Level
More
2 months 3 weeks ago #4551 by Doodah
1974 R75/6 Charging problems was created by Doodah
Hoping that someone can help. I'm a newbie to airheads and haven't really done any wrenching in years. This bike was a garage find, had been sitting for about 10 years and was in pretty poor condition with not much working. Speedometer shows about 52000, but from the condition of the bike and the wear on it, it could be 152,000 or even 252,000. In the past 3 months I've taken it mostly apart and put it back together so now it runs and rides. All lights work and the bike starts up on the first try and generally runs well. The problem is it's not charging and there is no generator light. I have replaced the following: Battery, Rotor, stator, voltage regulator, Diode board and most of the connecting wires. I've also replaced the old instrument pod circuit film with a new Katdash led unit. I've tried to follow the published troubleshooting as best as I could and can't get the light to light at all. I've checked terminals in the instrument pod and all seem to be functioning correctly. As far as I can tell, there's not much left to replace. Any suggestions would be greatly appreciated.

2016 R1200RT
1974 R75/6
Attachments:

Please Log in to join the conversation.

More
2 months 2 weeks ago - 2 months 2 weeks ago #4560 by Wobbly
Replied by Wobbly on topic 1974 R75/6 Charging problems
Welcome, and glad to help ! Here's 3 suggestions in order of importance....

1. One of the quirks of the BMW charging system is that the alternator will not work without a working warning lamp. When the bulb burns out, then the charging system stops working. Check the #194 bulb in the instrument cluster. This is a common bulb you can get from your LAPS. Do not fit an LED, it requires the resistance of a working incandescent bulb.

2. Although the OEM voltage regulators are sealed, they are still mechanical and give up after 40 years. I suggest one of the new adjustable solid state regulators. These are especially helpful if you installed an AGM battery in place of the original "flooded cell" type. AGM batteries require a slightly higher charge voltage than the original regulator is capable of, so you'll be "killing 2 birds with 1 stone".

3. Try new alternator brushes. Easily changed by removing the front engine cover.

Items 2 & 3 available HERE at the very bottom of the page.

Hope this helps.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 2 months 2 weeks ago by Wobbly.

Please Log in to join the conversation.

More
2 months 2 weeks ago #4561 by 8166
Replied by 8166 on topic 1974 R75/6 Charging problems
Some of the best money you'll spend on your new bike is for a copy of Rick Jones' book on airhead charging systems. He gives a breakdown (no pun intended) on the workings of each component, and step-by-step instructions for troubleshooting each one.

www.motoelekt.com/goodstuff.htm

When you turn on the key, and before you start the engine, the alternator light should come on. If it doesn't, start there and figure out why. Could be a problem with the brushes, a broken wire, a bad ground. Get the book and I bet in an hour you'll know what's wrong and how to fix it.

Better yet, get in touch with your local Airmarshal and see if there's a tech day coming up. Noting like knowlegeable, helpful, and cheery fellow Airheads to help you through to a solution, hands on, your hands on!

Good luck, and welcome to the ABC!

8166 Scot Marburger, This email address is being protected from spambots. You need JavaScript enabled to view it.
Check out the Yankee Hill AirTech Weekend, April 20-21, 2019

Please Log in to join the conversation.

  • Doodah
  • Doodah's Avatar Topic Author
  • Offline
  • R100 Level
  • R100 Level
More
2 months 2 weeks ago #4564 by Doodah
Replied by Doodah on topic 1974 R75/6 Charging problems
Charging Problem Solved!

Thanks for the responses guys. Much appreciated. I do have the book mentioned on order.

It appears that I had two problems. After replacing almost everything on the electrical system and still no Gen light, I figured it had to be a problem in the cord before it attaches to the instrument pod. I installed the resistor bypass between a 12V positive source and the blue wire at the VR to bypass the gen light. Then after hours and hours of studying all of Snowbum's info on the charging system, I finally focused on his discussion of a reverse magnetized rotor. So I rigged up a jumper, grabbed an old battery cable from the pile of parts and touched connected the battery briefly to the DF terminal for the rotor. After starting the bike, the multimeter showed just over 14 v when I rev'ed it over 3000. The Generator light still does not come on, so bad wire in the cord bundle is indeed likely. I have connected an inexpensive LED voltage regulator to the handlebars so that I can monitor the charging system. Now it's time to tackle all those other issues on the list!

2016 R1200RT
1974 R75/6

Please Log in to join the conversation.

More
2 months 2 weeks ago #4566 by Wobbly
Replied by Wobbly on topic 1974 R75/6 Charging problems
Very cool solution. Congrats !

Don't hide 'em, Ride 'em !!
#15150

Please Log in to join the conversation.

Moderators: 8166Wobbly
Time to create page: 1.295 seconds