The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: apull on June 22, 2015, 10:25:40 PM
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Need help 79 R65. Hit starter button it engaged then nothing. Now with key on the tach needle goes to 7000 and the starter relay hums when button is pushed. We are getting 7.4 volts to the starter relay. Pulled relay out applied 12v to it and it does work. Bypassed relay and starter tries to engage. These tests were done with battery charger. Battery measures 12.5v but will not do anything could it be a just bad battery? Any suggestions? All we have is owners manual it does have a wiring diagram.
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It does sound like the battery if it can only provide 7.2 volts to the starter relay. Might be worth having it load tested. Another option would be try a jump start from an other battery to see if that works which would then confirm the bike battery as bad.
Here's the best quality wiring diagram you will find anywhere. It will stand blowing up to a very large size.
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Barry, thanks for the wiring diagram. Am trying a battery first.
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Barry & All, It WAS the battery. I have never seen a battery fail like this. The battery was a sealed model, two years old. I had been for a ride two weeks ago no problems. when I tried to start it yesterday it turned over strong about two times and quit. NO headlight, nothing. With a battery charger hooked up all I got was a buzzing sound. Tested battery for voltage showed 12.4. Took it to Honda shop tested indicated internal short. $115.00 latter new battery problem seems cured.
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That is how my last battery failed. Check your battery charge voltage with the engine running ~3500 RPM.... I found out why my battery likely failed in that the charge voltage was over 15.5V - voltage regulator was bad and basically wasn't doing much in the way of regulating anymore.
It worked great right up until the point that it wouldn't work any more. It had enough integrity to light the idiot lights with the key on for the first 1 or 2 times of the starter, then voltage dropped below 10V and stayed there until allowed to rest for awhile.
A tell-tale with a bad battery/low voltage situation is observing the tachometer windup to thousands of RPM when the engine isn't running or even turning over - the solid state ignition is trying to come up to voltage, and failing because the battery isn't capable of producing the fraction of an amp it needs to get the electronics to their steady state, waiting for the trigger pulse from the crank sensor. Thus, the voltage at the coil (which is where the pickup wire for the tachometer is) undergoes alot of low voltages pulses in rapid succession - it doesn't take alot of voltage to run the tachometer, so it registers those pulses as the engine speeding up to 7K RPM. Usually it then collapses as the battery refuses to even give the small current anymore and it all sits still, dead. After given some time to rest/recover, it may be possible to get it to do the same thing over again. Repeat until you replace the battery...
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Checked the voltage regulator. We had 13.2 volts @ 3500 rpm. It looks like our problem was the 1yr old Chinese gel battery. The battery we got was made in USA for a Goldwing fit great.
Thanks for all the help.
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Checked the voltage regulator. We had 13.2 volts @ 3500 rpm. It looks like our problem was the 1yr old Chinese gel battery.
The battery may well have been the problem but 13.2 volts isn't wonderful as a charging voltage. It should be 14.00 volts and ideally a few tenths higher especially for an AGM or Gel battery. Depends how it was measured though. If that was measured using the new battery and the battery was fully charged then it's definitely too low. If it was the old battery and only partially charged then it might not be so bad and you'll get a higher reading with the new battery.
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like Barry said
13.2 @ 3500rpm is not real good for a fully charged battery
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Thanks, Will check again after the battery is fully charged. How hard is it to change the voltage regulator? One thing leads to another. Andy
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Should you decide to replace the VR, perhaps contact Rick Jones at Motorrad EleKtrik and check out his solid-state VR. I replaced the vintage OEM VR on my '81 R65 and have been very satisfied with the electrical upgrade.
http://www.motoelekt.com/
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How hard is it to change the voltage regulator?
Couldn't be simpler. remove the tank and the big metal can with yellow tape at the bottom is the voltage regulator. It's an electro mechanical device hence the size of it. A new electronic one will be vastly smaller but the connections will be the same. Ignore the black thing with coloured wires coming out. You won't have one of those as that's my bespoke ignition amplifier.