I use plain old chrome polish to clean the slip rings, followed by a wipe-down with electrical contact cleaner to remove any polish residue. Yes, I remove the stator, but just swing it off to the side and rest it on some wood blocks. Here's one ring cleaned, the other not .....
View attachment 250070
..... and both done .....
View attachment 250071
I know Gary likes to leave them dirty but over the years I've encountered a few bikes that actually quit charging because the rings got too dirty. So, I like to start off on a new-to-me bike with them clean. After that, I can monitor them and let them get dirty again, to a point, then clean them again if need be. But honestly, after my initial clean-up, I haven't needed to re-clean any yet.
DTTBFTD LOL
Yes if it's a new to you bike and rings are "dirty", by all means clean them. Did a bit of digging and in industrial use, the suggested copper ring surface finish roughly translates to 320 grit sandpaper.
IIRC 2many found the reference; a carbon trace transfer to the rings is necessary to proper operation. But a mottled appearance may indicate the black build up is also grease or oil, not
just carbon from the brushes, that oil grease dirt deposit will increase resistance between brush and ring, reducing the charging system effectiveness. The brush compartment is not "sealed", some add openings for "cooling" but I don't do that, introducing dust, grit, oil water etc. that may get on the slip rings, not a good thing.
So; clean the slip rings, lightly scuff with 320 or finer sandpaper, scotchbright is acceptable, look at the area to see if oil from a nearby leaking seal gasket etc. is present. Remove any oil from rings stator, rotor etc.. When done sanding follow up cleaning rings with rag, contact or carb cleaner, till the rag stays white. any abrasive grit left behind is a bad thing. You don't need to create a shiny or gloss surface on the rings. If there is no oil present during periodic inspections, a bit of carbon transfer on the slip rings is fine, desired, carry on! There is an acceptable brush ring resistance value, I might check measure some working sets, report values for a reference.
@Jim May have some comments also. ;^)
A tidbit found while researching: "The reason the positive brush wears out faster is that current goes from - to +...Therefore, 70% of heat generated at an arc is on the positive side." This agrees with what I find, the + brush typically wears at about twice the speed of the grounded brush.
DTTBFTD (dragging this thread back from the dead) it's a gggGary thing.
It's possible to have runout on the rings from poor fit of the rotor on the crankshaft taper. If you are having issues with charging, worth checking, cleaning the taper surfaces..
) I wrote down the formula for "area of a circle."
