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Charging system question

c20500

c20500

Just got it firing!
Joined
Nov 14, 2008
Messages
18
My 86 LM's alternator rotor measures 3.1 ohms across the slip rings and there is a small leak at the tapered shaft - seal behind the rotor.
The warning light, does not light up at all, bulb and connections are fine. The charging is just adequate to keep the battery at around 12.35 volts after an hour ride. The regulator is working fine. All the diodes seem to test fine.

Is the ohm reading on the rotor too low for the charging system to work well? I do notice a decrease in system voltage as the bike warms up ( output is best when cold )

Also, can the seal behind the rotor be replace from the front or do you have to pull the front cover?

Appreciate any comments.

Thanks!
 
And yes, the seal can be replaced by removing the cover, stator and rotor (use the right rotor pulling tool) and prying it out and bashing in a new one.
 
take the spade off the slip ring terminal and touch it to the stator body or the timing chest making sure it contacts and see if the light comes on. If it does it is almost certainly a problem with the rotor.

Take the rotor off and check for continuity between the slip rings and between the slip rings and the poles of the rotor. there should be continuity between the rings but nothing between the rings and the poles.

Pete
 
3.6 ohms across the slip rings is about right, but now try measuring this across the brush terminals, having removed the wires. Bet the brushes are giving a poor contact with the slip rings.
 
Peter,

I did get the charge light to go on when I connected the slip ring connector and grounded it.

I didn't have a chance to check continuity on the poles to the rings... if the rotor is supposed to have 3.4 ohms and I have 3.1... that's aprx reduction of 10% which is about what I'm missing... It's pretty dirty and with the oil that's been weeping out the the seal maybe it's toast...

I also want to confirm that I can replace the seal without remover the front timing chest cover!?

Thanks to all for your input
 
Charles,
It is best to replace the seal with the cover off. The crank nose makes it difficult to drive the seal correctly. Once you have the alternator off (hardest part of the job) it is just the front engine bolt and cover screws that need to be removed. Also while the cover is off, check the timing chain and adjuster. If necessary, you have done most of the work required to replace the chain, and update the adjuster.
 
A relatively thin-walled deep-well socket makes driving in the new seal a snap with the cover on.
 
I replaced the rotor and the charge light still doesn't even come on although it will go on when I short the connector that goes to the positive slip ring. Can the rectifier still work properly with the charge light part not working? The charging seems ok now and I have a volt meter anyway. Any feedback would be appreciated.
 
You turn on the key, and no light. Yet if you short the slip rings, you get a light?

Measure the voltage from gound to each slip ring with the key on.

You make it sound like it is simply a bad connection on a brush.
 
had a bad connection at the rectifier and I installed new brushes... All working fine now. Thanks for everyone help.

Seasons greetings!
 
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