Starter motor grounding

I've been having intermittent problems with the electric starter motor on my '79 KZ750. It seems like sometimes it fails to ground internally.

So I've got a couple questions. First question is where does the starter motor connect to ground internally? I'm assuming it's between the tip of the armature and the end cap of the housing. Is that right?

Also, I'm missing two of the thrust washers from this end of the starter. I have one very thin washer and one much thicker. I've tried some starter rebuild kits and none of the washers they include have fit this spot. I'm wondering what I need in order to properly replace these. Should there be two of each (two paper thin, two thicker)?

They're both pretty corroded and I'm wondering if the washers play any role in the ground connection. Does the armature ground through these washers or does the tip of the armature connect directly with the housing?

You brushes, one is positive and the other negative. Connection to the post at the positive battery, then inside to the brush. Then the ground goes from the case, inside to the other brush. Those are the two circuits.
I know you've tested and tested, but there may well be something in the battery cable/ or connection there.
I found where someone had replace just the end and about 1 foot of cable today. It had one of those bolt down clamps around the wire. Well it failed, but had worked for several years. I ripped that crap out and made up new cables. Problem solved.
Maybe you have a bad end or something on a cable? Pretty cheap to replace them. Buy some bulk cable and some ends to either crimp and solder or just solder, Heat shrink etc.

The brushes are #5 and #9 is "as required", as in might not need all of them.

What makes you think it's the starter itself that's bad? You're certain it's not the starter clutch, starter solenoid, starter button, or something else that's bad?

When the starter completely fails (it's happened about 3 times now) I can take the starter off the bike, hook it to a battery and it doesn't spin.

Take the starter apart, put it all back together, hook it to a battery and it spins right up.

I really think when this happens, it's not grounding properly inside the starter. It's not a cabling, solenoid or other issue. It's something internal in the starter. Reassembly seems to fix it for a while, but then it comes loose again.

I've replaced the brushes and bearing, tested the armature. I'm missing two of those washers, but otherwise things look good.

The motor occasionally makes a little squealing noise when it stops (see video below).



That seems to be happening in the end cap (#1 in the diagram). I took the other end cap off and hooked it to a battery and heard the sound. Inspected the tip of the armature where it meets the end cap and noticed a few little scratches/gouges. I sanded those down before reassembly this time.

I really think this all adds up to something not aligning properly in that end cap (#1). The armature must be moving a little causing it to wear and sometimes it shifts enough to loose ground.

So, does anyone know the thickness of these four washers? And does anyone know if the armature is supposed to directly contact the end cap or if it connects to the housing and grounds via the washers?

Perhaps it will help if I explain how the starter works.

As mentioned earlier, there are two brushes, one negative and one positive, that ride on the end of the armature. When you look at the armature where the brushes ride, you see a whole bunch of little strips of copper. Each one of those little strips are connected to the end of a wire, in such a manner that all wires have a strip at both ends. When the positive brush is touching a strip, thus connected to a wire, the negative brush is touching the strip that connects to the other end of the same wire, and electricity flows from brush to brush. Since the positive brush is connected to the positive cable post on the outside of the starter, and the negative brush is attached to the rear plate on the starter, that means the electricity flows from the positive cable, through the starter armature, to the negative brush. to the outside case of the starter, to the motor, through the contact at the rear where it bolts to the motor, and through the front where it contacts the motor. through the motor to the negative battery cable, back to the battery.

A little trick that sometimes works is to smack the starter with a hammer when it's not working, I've got many vehicles off the road and back to the shop by doing that.

You can also take the armature out and take it to a starter/generator repair shop and ask them to check it. They can stick it on a device called a "Growler" to see if all those little copper strips are still connected and conducting. If one is not conducting and the starter stops on it, it won't work again until the armature is turned. Could be your problem.



HTH

Steel, that's really helpful. But I'm still not clear on where the grounding connection to the housing happens. You say "the negative brush is attached to the rear plate on the starter".

Where does that connection happen?

the negative brush is grounded to #6 in the above diagram, wherever that plate contacts the housing is where it's grounded. The armature shaft should never have electricity flowing through it, all those wires are insulated from it.

Of course the outer windings are powered also, but that just turns them into electromagnets I don't believe I've ever seen one of those go bad. They can be checked with an ohm meter if desired.

The three most common problems with starters are:

(1) Bad bushings, the ones that support the armature at each end. If they are bad they allow the armature to contact a winding, at which point it no longer works (that's where the hammer thing works).

(2) Worn out brushes. Means the brushes are no longer pressing and against the armature and operation can be intermittent.

(3) Armature worn down to where brushes are no longer making good contact. Same symptoms as #2.

Other things can go wrong, but those are the most common for starters in general.

If a guess is okay, the "starter brush holder" shown on kawasaki.com -- without a part number -- is likely akin to the following generic example which illustrates how the negative brush grounds via the holder, while the positive brush is insulated from the holder.







Good Fortune!

That's exactly what I was looking for. It's totally not what I was imagining, therefore incredibly helpful!

Topper wrote: That's exactly what I was looking for. It's totally not what I was imagining, therefore incredibly helpful!

I think Patton ought to change his name to "Incredibly helpful", cause he really is.

Be sure to click on the "Thanks You" at the bottom of his post, he goes the extra mile and then some!

Whoops! I see you already have

Ok, the starter motor started squealing every time I started the bike. So I pulled it once again.

Time to rebuild it right. I'm going to replace the missing washers, but I wanted to ask about what kind of grease I should use and where.

The manual says high temp grease on the planetary gears. Is bearing grease good or do I need something more specific for this job?

The squealing noise is coming from the right side of the starter (opposite of the planetary gears).

There's a spot where the tip of the commutator meets the end cap (#1 in the diagram I posted earlier). I've read that the brushes and commutator need to be clean and free of grease. But what about this spot where the commutator sits in the end cap? It seems like that's where my noise is coming from.

I've read that the brushes themselves wear and the graphite dust provides the lubrication needed for the commutator.

Could/should I put a little graphite dust on the tip of the commutator to prevent the squealing noise?

An intermittent starter, if the connectioons are all good and the battery is charged can usually be traced to the brushes and commutator. You know what the brushes are. The commutator is the thing the brushes ride on. It consists of the copper segments and the insulating segments between the copper ones. When rebuilding a starter the commutator is usually put in a lathe and a light cut is made on the commutator, enough to "clean it up" no more. That is, the copper segments should have no marks on them from the brushes. After turning, the insulating segments are "undercut". They must be cut lower than the copper segments so the brushes don't contact them thus holding the brushes off the copper segments and causing a dead starter. Disassembling and reassembling the starter can temporarily cause the brushes to contact the copper segments again but soon the starter quits again causing you to pull handfuls of hair out of your head. The undercutting is usually done on a special machine but can be done on the lathe with a specially ground tool bit and a little care and patience.

The squealing you heard is most likely caused by a worn/dry bearing or bushing. If the radial play in the bushing is minimal, it and the shaft can be cleaned and lubed with moly grease and put back in service. If the bushing is worn it should be replaced.

The washers/shims on the shaft mearly control the end play of the armature. If one thin one is missing the starter would probably still work but will wear the commutator prematurely.

There aren't a lot of shops around that rebuild starters any more, except the large re-manufacturers and they probably wouldn't even look at a moto starter unless they had a thousand of them to do. If you can't do it yourself or find some one local to rebuild it, send it to me and I'll rebuild it for parts cost and shipping. PM me if interested.