'79 R65 Dies at Idle

[noah]

Hi everyone,

I once knew the solution to this problem, but its been a while so my brain is rusty.  The bike starts fine with a jump, the battery is solid (I've had it tested several times) and it even idles well if the choke is on.  But, as soon as it starts idling low enough for the red "laurelauf" or whatever that light says, to come on, the bike dies.  It won't even start without a jump; if I try it almost immediately starts making that terrible clicking sound.  

I have a feeling this has something to do with the alternator or rectifier but I forgot what exactly the procedures are for testing these things.  It has something to do with a voltometer and testing one or other of those parts somehow when the bike is running.

Can anybody refresh my memory and/or offer other suggestions.

Thanks!

[MrRiden]

Sounds like you may have several issues, a compound problem as it were. What year R65 are we dealing with here? Get a hold of a volt / ohm meter. Were going to go after the starting issue first. I want to see what the battery voltage is at rest and what the voltage at the battery terminals is when you push the start button. Others will chime in shortly to guide you on this and have you start checking coils, carbs and so on. Grill is hot, gotta run.
rich

[noah]

shoot.  I forget to test when I press the start button.  Here's this for now, then I'll run down and do that:

OFF: 12.1 v
ON: @ 1.5rpms -- between 8.5-8.7 v.  Voltage dropped as rpms increased and visa versa.

When I turned it off after testing, the volts slowly climbed back up to 12.

Back in a sec.

Oh, and its a 79 R65 with 65,000 miles.  It sat for a couple months because I couldn't figure out this problem but now it runs fine when it runs.

[noah]

Ok, here's the news:

OFF: the battery was about 11.8 volts.
On: with headlight on about 9 and change volts.
Starter depressed: 7.4 volts and dropping

When I pressed the starter, the bike made a very slow, gutteral, clicking/chugging sound and the volts dropped to 7.4.  When I held down the starter for a couple of seconds the volts slowly dropped till I let go at 6.8 volts.  When I tried to repeat the test, nothing happened when I pressed the starter.  No sound, no drop in voltage, nothing.  This is how it usually goes until I jump the battery again.

Help . . .

[Ed Miller]

Did you charge the battery before your tests?  If so, it is definitely dead.  If not, charge it up and repeat them.  If it shows good with a full charge, then you need to test the bike's charging system to see why the battery runs down.

I killed my Triumph's battery the other day by leaving the key on.  I hope I didn't cook a coil as well.  

[noah]

Did you charge the battery before your tests?  If so, it is definitely dead.  If not, charge it up and repeat them.  If it shows good with a full charge, then you need to test the bike's charging system to see why the battery runs down.

I did charge the battery and ran the bike before the tests.  I've also taken it into to auto shops several times and had them trickle-charge it overnight and then test it on their machines.  Every time they tell me the battery is fine, so I'm inclined to think that the battery is not the problem.  Also, the bike will run fun when I ride it until I come to a complete stop or try to move out of first, when it dies if the rpms get too low.  This also makes me think its the charging system and not the battery.  

How exactly to I go about testing the charging system to isolate the problem?

[MrRiden]

To check the charging system the method I know of is to have the bike running [you'll need to jump it again] and check the voltage once more at the battery terminals. Above idle at oh say 2000rpm you should see 13 volts or above. If its below 13v at running speed the regulator or generator may be faulty but first clean up all your electrical connections at the regulator. There is a simple way to jump the regulator with a short piece of wire but I can't recall which pins get jumped.

[Justin B.]

If your "fully charged" batter reads only 11.8 volts then it is most likely bad or was not charged.  A fully charged battery, at rest, should read over 12.5 volts.  Also, as your voltage drops when the RPMs go up your charging system is not working and could be the root cause of your ailing battery.  Batteries do not like sitting around in a less than charged state...

[noah]

but first clean up all your electrical connections at the regulator.

How exactly do I do this?  Assuming it is the charging system as Justin indicates, now what?  What's the next move, in baby steps please.

Thanks

[Ed Miller]

Here's a set of articles on the electrical system.  He's long on explaining how it works, but in fact, these bikes don't have a particularly simple charging system.

http://bmwmotorcycletech.info/boxerelectrics.htm

http://bmwmotorcycletech.info/electricalhints.htm

http://bmwmotorcycletech.info/trbleshootALT.htm

[Justin B.]

Ed, do you really mean "do have..." ?

[noah]

Thanks for the crash course in electrical engineering, Ed.  It was very informative.  

I still need to know what the next step is to isolate my problem.  The volts do indeed drop as the engine accelerates.  This probably means there is a problem with the charging system.  Good, got that covered.  What I'm still not clear about is how to move forward in diagnosing specifically what part of the system is giving me static and how to fix it.  

Does "clean up all your electrical connections at the regulator" mean remove them from the terminal and hit them with a brush?   :-/

Should I test the resistance on these wires or is the problem something internal to the regulator?  In which case then what?  Replace? Jump using the unknown method that Mr. Riden suggested?

Help . . .

[MrRiden]

OK I found it. Remove the Voltage Regulator from its socket. You should see 3 female connection points. If yer really lucky they will even have identifying letters [or look on the regulator itself for corresponding id letters] They will be marked f+, f- and Df. We want the f+ and Df connectors that are directly opposite each other. The wires will be Blue and Blue with a black tracer or even all black. We DO NOT want to use the brown wire. Make up a handy little jumper wire with a male spade connector on each end [you now have a new tool for your on board tool roll] insert the jumper to connect the f+ and DF wires to each other [blue & blue black]  Get 'er started however ya need to and check the voltage at the battery terminals. Got 13-15 volts? Go to your local auto parts store and get a Borg-Warner R-588 or Neihoff WA 709.
A good parts counter person can cross reference against either the Borg-Warner R-588 or the Neihoff WA 709 numbers to find one that werks. I suggest these because they are half or less than the BMW part.
If however you jumper out the regulator and still do not see sufficient charging We're going to take off the front engine cover[ disconnect the battery first!] and begin by checking all the connections [clean / tight / connected] at the diode board. You may also have bad brushes on the alternator [not hard to change but fiddly] or the most expensive, open alternator windings. Lets go for the regulator first 'cuz it's cheap and easy.
rich

[tagordon]

Noah
Do Not Remove the engine front cover without disconnecting the negative battery cable.

[farmer]

Don't forget to check the alternator. I had very similar problem with my R100M. I checked everything I could per the manuals, but could not isolate problem. Finally took it to dealer and found out the alternator rotor was bad. Rebuilt one fixed the problem.