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AC808

S/G rebuild questions

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AC808
I have a S/G that has been turning over quite slowly. I put another one on in its place. That spun quite fast. Am i safe to assume that the brushes are the culprit in the slow turning one? Or something else.

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ZippoVarga
Jay, There are many factors in what makes a S/G a good unit, and a bad one. My suggestion is to take the Armature out and clean the commutator grooves. Often carbon build up causes a jump effect with these units which robs power on both the starter and generator sides of the unit. Also check for lateral groves on the laminations on the armature (grooves that follow the lamination stack instead of opposing it). This would indicate a "rub" caused by worn top or end bearings or in rare instances a loose pole shoe. IF you find this to be present then I suggest finding a local automotive electrical shop to have the bearings in the tail and end cap replaced or the pole shoe tightened. If you are still charging and still have "some" starting capabilities then your problem is small thus far. Give the armature a cood cleaning (via compressed air and a scratch awl in the grooves of the commutator which is the copper piece the brushes make contact with), check for at least 3/8 of an inch left on the brushes and if less then replace. Your local automotive electrical repair facility should have these readily available should you need them. Then reassemble the unit, polarize by touching the battery to ground for just an instant then hook it up and give it a try. By polarizing the unit your actually de-gausing(de-magnetizing) and thus giving the unit a clean field of direction for initial start up after repairs. I've experienced non-charging units that only needed this measure to get them to charge effectively. This method works for starting as well. Another measure of defense is to have the regulator checked to make sure it's parameters are with in the limitations of the S/G. Takes a couple minutes on a test stand but can save a few bucks on a repair as a regulator that closes too late can cause the charging side to burn out resulting in $$$$ to repair. Hope this helps!! Sean

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Agricola
Sean, I agree on most of your stuff. We used to undercut the commutator with a broken hacksaw blade. You snap a blade in half or so, tape up the teeth and use it to cut down the insulator between commutator sectors. As for the polarization, don't you go between the B & A terminals on the regulator? That way the regulator and generator are polarized the same.

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HubbardRA
You only have to polarize a generator. The starter-generator is self-polarizing whenever you engage the starter. Two items are usually the culprits. 1. Worn brushes and or commutator, which produce resistance to current flow. 2. Worn bushings or bearings which allow armature to be off center and therefore not produce the proper magnetic force to spin the starter properly.

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JJ MARSHALL
if you would like to see how good it will spin off the tractor get a set of jumper cable or a jumper box and hook the + cable to the termail mark A and hook the - side to frame of the S/G the take a jumper wire and hook it to the - neg cable then touch it to the termail marked F. be sure to get a good grip on the S/G it mite jump out of your hands. JJ

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