'73 R75/5 SWB. No Charge Light. No Crank. Help!

[Tom H Ca]

As the tile says, my '73 SWB is having the issue of no charge light and no cranking.

I did do some research on this and checked the likely suspects. The rotor is normally the issue.

I removed the negative cable and pulled the front cover. I tried the test of connecting the two brush wires and the charge light lit with the battery connected again. Then went on to pull the stator so I could do a decent test of the rotor.

I first found that the rotor slip rings a perfect continuity even though they should be about 8 ohms resistance, Hmm??

So I read about another test that said to have the charging system together and put a screw driver between the slip rings to short them together, I put everything back together and pushed in the key and the charge light lit????

I figured the slip rings were dirty. Pulled the stator and cleaned the slip rings. Now I have the about 8ohms resistance. Good so far.

Brushes are about a 1/4 inch or so down so that when I put the stator on, I have to push them up about that.

I put the bike back together and the charge light was on and it started fine for two days in the garage. Then...

I went to take it for a spin, and no charge light again, so no crank???? I used the kick starter to turn the engine through, still no light. Let it sit for a day or two while finishing up another project. Went to push it on my lift but decided to check. Behold, the charge light was on and it started.

It's now on my lift. Went back to start working on it a few hours latter, no charge light again???????

I was thinking a bad wire and when I turn the bars the wire has an issue. But in between loosing the charge light, the bars were never moved. When I tested on my lift and the light came back, bars never moved.

So... I'm thinking a new rotor??? Maybe a new starter relay????

Right now it's unreliable if I take it on the road and stop somewhere. Maybe it won't start?? I could use the kick start, but never had any luck with it unless the bike is already warmed up.

Any thoughts before I find a good used rotor??

Maybe.....What can I do to easily change the starter relay and make it not have the no starter button when the bike is running? Latter model plug and play without this feature??

Thank you~
Tom

[Tom H Ca]

Well... I was hoping for a bit more info, but I think I have it fixed.

I tested the rotor again this time on the bench. It would Ohm fine and then not when I turned it to see what would happen if I rotated it 180 degrees. Repeated this test a few times and finally decided it was a bad rotor.

Went down to my local Guzzi shop that has used parts. Same rotor as most Tonti frame bikes. Found a good one and installed it. So far so good. Have to try pushing in the key a few times over the next few days to see if the light stays lit when I do. If so, I'll take it for a spin.

Hopefully fixed!
Tom