Battery light came on and stays on

[wingnut]

'02 RT with 43K; no accessories; 1 yr old oddessey battery. Just changed fluids: engine, tranny, diff. Went on short 15 mile ride to leak check - all OK. Then, near home, battery light came on. Will check battery connections and alternator belt first thing this AM. If not the connections or belt, what would be the next step in troubleshooting? TIA

[Paul Mihalka]

"battery light" is a wrong name. Consider it a charging system light. With the light on you may have a perfectly good battery but it is not getting any charge. My bet on a 43K bike would be the belt, especially if it was never changed.

[bmwmick]

Once you verify the belt is OK, look at the small blue wire on the back of the alternator. This is the DF+ wire that provides the 'exciter' current for the alternator. If that wire is grounded anywhere between the instrument cluster and the alt. it can cause the 'light on' symptom.

 

My guess is the belt broke.

 

Mick

[wingnut]

Correct on the belt, guys. New one is installed but I'm scratching my head trying to get tension on the belt. The adjusting nut (on right facing rear of bike) does not seem to adjust - just tightens up. I'm going to search archives.

[Barglowski]

Two ways to get tension:

1) use a large screwdriver between alternator and engine.

2) use torque wrench on that adjusting bolt. Trick is that the bolt is reverse threaded! Note that the adjusting bolt causes the bolt to "climb" a "helix". Then tighten the other alternator bolt when at the proper torque.

 

Instead of torque, you can always adjust to "just barely twists to 90 degrees" at the midpoint of the belt...

 

Later,

jan

[Jim Moore]

BMW makes a tool to tension the belt, but there is an easier way. Put a nut on the adjuster post. Tighten it so that threads are visible, then put on another nut. Tighten that nut down against the first nut, then use a torque wrench on the second nut to tension the belt. While holding the alternator in tension, tighten down one of the other nuts on another post to hold the alternator in place. Voila!

[wingnut]

Thanks fellas. Carefully levered the alternator up and have a 90 degree twist in the belt. Only took 2 trys I will check tension in 6k. I feel like a ride

[Ken H.]

Carefully levered the alternator up

Glad you got it, but for future reference and the benefit of others that this thread may have not made clear...

 

The alternator is held in place with three bolts. One at the top, one on each side. Looking from the front of the bike at the belt/pulleys, the right bolt has a ratchet affair behind the alternator mounting plate that when turned pilots the alternator upward. That is what you put the special BMW tool on, or as mentioned two jamb nuts, then with a torque wrench you rotate the bolt, pivoting the alternator and tightening the belt. While holding the right one in position you then tighten the left one to hold the alternator in place. It's not as cumbersome as it sounds.

 

If you prefer to set the belt to 90 degree rotation instead of a torque value, the mechanism for adjustment is still the same.

[wingnut]

Thanks for the clarification, Ken. With a long extention for the 13mm socket, it is pretty easy to tighten the left bolt while levering tension on the belt. Glad I carried a new belt in the tail section. Will get a new "spare".