Boxerworks.com

1984 R100

So I'm out for a ride and go to start the bike and all I get is a click.
My battery (Dekka EXT16L) is five years old.
So I use the kick starter and it fires right up.
I'm thinking maybe I left the tail light on by accident. (park key position)
Go off riding thinking I need a new battery. Later that day same thing. Except I hit the button again, and it fires up.
Back at home I charge the battery (it shows full charge) then try to start it and all I get is the click.
But if I press the button again, it starts normally several times in a row.
Go away, battery on charge, come back and get the same result.
All I get is a click, then push the button again, and it starts normally several times in a row.
Any thoughts?

Thanx ZM

Starter relay? My R80 used to act like that sometimes, had to replace the starter relay several times for some reason.

First thing to check is the battery terminal. A bad connection there could provide enough amperage to drive the relay and solenoid, but not enough to drive the starter. Check the voltage when you hit the starter button and hear "click". If the voltage drops significantly, you still might have a bad battery....voltage without amperage.

where is the click coming from?
If under the tank, it's the relay making the noise.
If under the engine cover, it's the starter solenoid making the noise.

So if it's under the engine cover, I'd say the relay is good and either the solenoid or a bad spot in the starter.
If it's under the tank, it could be the the relay, or still the solenoid.

How much work do you want to do? You can pop the tank off. Then you can test the relay.
Or take the engine cover off to see if you're getting power to the small wire to the starter solenoid, which is powered from the relay.
If you get power there, the relay is good. If no power, the relay is bad.
If the relay is good, you're probably looking at a bad starter or solenoid.

AGM battery. In my experience, 5 years is a long time for a battery. Could be signs of age. Have the battery tested.

Kurt in S.A.

So after re-trying after the initial attempt the starter turns the engine over easily. The relay seems a possibility, but I can't seem to find the part on airhead parts websites.
Could it be that on the '84 it has a different system that goes directly to the solenoid?

For the '84, the starter relay part number is 61 31 1 243 207.

Kurt in S.A.

Kurt in S.A. wrote: ↑Sun Sep 22, 2019 6:29 pm For the '84, the starter relay part number is 61 31 1 243 207.

Kurt in S.A.

Thanx Kurt! Where on the bike is this located?

Should be under the tank, left side of the backbone IIRC. It's a small cube, about an inch on a side.

Kurt in S.A.

Kurt in S.A. wrote: ↑Sun Sep 22, 2019 6:51 pm Should be under the tank, left side of the backbone IIRC. It's a small cube, about an inch on a side.

Kurt in S.A.

Yes, it's as Kurt says. It bolts to a bracket welded to the frame. Depending what equipment you have on the bike, there may be another relay there as well... the one you want should have 5 terminals, two of which will be connected to quite thick red wires. It's worth noting that, if you disconnect both red wires, nothing at all will work because these constitute the main positive feed to the bike circuits. For some reason best known to themselves, BMW decided to route the feed through the relay using two permanently linked terminals. No rhyme nor reason to it as far as I can see, but that's the way it is.

Good luck with your trouble shooting... intermittent faults are a real PITA.

Rob

Snowbum makes the suggestion to connect those two red wires right where they come in and out of the relay...one has to shave off the insulation, solder a jumper wire, and carefully cover with probably liquid heat shrink, etc. This bypasses the issue of, as Rob says, the relay going bad and the pass-through red wires can't simply pass the current.

Kurt in S.A.