Starter armature, is it good?
- Thread starter old31
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Joe K
Well-known member
You can't really tell without a "growler."
As far as the commutator itself goes, yours is not bad. It could stand to be "undercut" - which you can do approximately with an X-acto knife and being sure to not leave sharp edges at each segment. But a problem might be in the wiring which goes between segments. If one of these is grounded, you can't really tell from looking.
A "Growler" is basically the magnetic part of a transformer. You put 120VAC into the growler side, and if there is a short, the coil acts as secondary circuit. A growler typically is used with a thin piece of metal - think thickness gauge. You hold this in your hands and between poles of the armature going around pole by pole. And if the 60hz "buzz" is felt by the thin metal, that particular pole is "shorted."
More at https://en.wikipedia.org/wiki/Growler_(electrical_device)
If you go all the way around turning the armature in the jaws of the growler and holding the metal and no attraction is felt, then you have a good starter armature.
They may have a growler tester at AutoZone.
A dead segment is not a death knell - the starter may still work, but tend to "hang up" and not start at certain spots. If you can move it with your fingers, you might get it to go.
Joe K
As far as the commutator itself goes, yours is not bad. It could stand to be "undercut" - which you can do approximately with an X-acto knife and being sure to not leave sharp edges at each segment. But a problem might be in the wiring which goes between segments. If one of these is grounded, you can't really tell from looking.
A "Growler" is basically the magnetic part of a transformer. You put 120VAC into the growler side, and if there is a short, the coil acts as secondary circuit. A growler typically is used with a thin piece of metal - think thickness gauge. You hold this in your hands and between poles of the armature going around pole by pole. And if the 60hz "buzz" is felt by the thin metal, that particular pole is "shorted."
More at https://en.wikipedia.org/wiki/Growler_(electrical_device)
If you go all the way around turning the armature in the jaws of the growler and holding the metal and no attraction is felt, then you have a good starter armature.
They may have a growler tester at AutoZone.
A dead segment is not a death knell - the starter may still work, but tend to "hang up" and not start at certain spots. If you can move it with your fingers, you might get it to go.
Joe K
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Patrick L.
Well-known member
Was this starter working before it was taken apart ?
If it was then then it should be good. The commutator should be cleaned up/cut and the mica doesn't need to be cut on a starter.
If it wasn't working or you don't know then its as Joe said. A growler is needed with someone that knows how to use it. A continuity check can/should be done on the commutator.
If it was then then it should be good. The commutator should be cleaned up/cut and the mica doesn't need to be cut on a starter.
If it wasn't working or you don't know then its as Joe said. A growler is needed with someone that knows how to use it. A continuity check can/should be done on the commutator.
Starter armature segment insulators do not get undercut as those in generators. The commutator surface SHOULD be smooth. NO GROOVES. Starter brushes are copper/bronze as opposed to carbon brushes in generators. Grooves between the segments would cause the brushes to wear more quickly and throw off deposits that can short the segments.
Synchro909
Well-known member
I was always told this to be the case. If the starter is working, leave it. Maybe a cleanup with a solvent like brake cleaner on a rag but that's all.
Brian in Wheeling
Senior Member
What Bob said in #4 above.
Brian W.
Brian W.
rotorwrench
Well-known member
The brushes have a hard time with the mica between the segments if the segments wear down to flush or lower. It's funny how the copper will wear faster than the mica. The mica should be undercut a bit on all armatures whether it be a generator or a motor or the brushes will start to bounce around on there and not make as good a contact as they should. They will wear faster the more rough the surface is. When you have a starter that uses copper based brushes is when you can get away without undercutting but those type generally have micarta between the segments so that it will wear along with the copper.
Electrical shops have a neat little tiny motor driven cutter that is part of a small armature lathe set up to just cut straight down between each segment but they can be cut by hand with a real thin coping saw blade or similar thin saw blade. They only need a small amount of mica removed.
The good growler sets usually have a test lamp set up built in to check the commutator segments for continuity and shorting as well as the inductor set up to check for armature winding shorts that cause magnetism in the core segments. Generally, a hack saw blade is used for best results.
Electrical shops have a neat little tiny motor driven cutter that is part of a small armature lathe set up to just cut straight down between each segment but they can be cut by hand with a real thin coping saw blade or similar thin saw blade. They only need a small amount of mica removed.
The good growler sets usually have a test lamp set up built in to check the commutator segments for continuity and shorting as well as the inductor set up to check for armature winding shorts that cause magnetism in the core segments. Generally, a hack saw blade is used for best results.
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Patrick L.
Well-known member
I have one of those tiny motor driven cutters. It doesn't get used on a starter. The commutator gets lathe turned.
Strange but the growler grew legs years ago, sure wish it hadn't.
Strange but the growler grew legs years ago, sure wish it hadn't.
Kurt in NJ
Well-known member
Whem using a growler there is another test that is rarely mentioned, a output test, it's not as dramatic on a starter as a generator, the growler induces a alternating magnetic field, it can be measured as ac amps and each bar / winding can be checked, with a generator 10-20 amps, but with starter it is 2-5 amps, this will show the connections of the windings to the commutator
The Ford starter has hard copper brushes with high spring tension, this will wear the mica at about the same rate as the commutator bars, there are also starters with copper/carbon (much softer) brushes, these commutators are undercut
the original posters armature appears to be good in the commutator area, it has been turned, and though the turning wasn't carried all the way across it looks to good enough
I looked for a you tube video, but didn't find what I wanted, guess it is one I should make
The Ford starter has hard copper brushes with high spring tension, this will wear the mica at about the same rate as the commutator bars, there are also starters with copper/carbon (much softer) brushes, these commutators are undercut
the original posters armature appears to be good in the commutator area, it has been turned, and though the turning wasn't carried all the way across it looks to good enough
I looked for a you tube video, but didn't find what I wanted, guess it is one I should make
Joe K
Well-known member
I like that test because it actually uses the generator/starter winding as the "secondary" winding of a transformer. Its probably more accurate than the "thin metal attraction" - the way its usually done, since it identifies EXACTLY which winding is open.
The downside and why it is not more frequently done is because by the time you fail the vibrating metal part of the test, you realize you're into rewinding the entire armature since almost no matter where the failure is, you have to first find the "last" winding done - and unwind from there - layer by layer.
And if you're like me, you ALWAYS find the failed coil on the "next to last" coil removed - or at least the second half.
"Random failures ALWAYS result in the maximum work/difficulty possible."
I think that's a Murphy sub-corollary.
The "LeJay Manual" is a good reference source for Model A generator/starter winding diagrams AND making your own ersatz Growler from a Model T generator/starter part.
https://www.scribd.com/document/3093121/LeJay-Manual
Plan 22
Joe K
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Keith True
Well-known member
I don't get too excited about the mica wearing faster in an A starter.That starter turns around 1500 RPM while cranking,and it only turns a short amount of time.If I remember right the generator turns around 3000 RPM with the engine at 2000 RPM,and it spins every second the engine is running.Those high amps running through a 6 volt starter can really melt the edges off the commutator if you undercut.That has been the only real starter component failure I have had on an A.In the mid-70's I undercut mine because I thought it was the proper way to do it.It lasted the summer and sort of melted the bars all together.
Kurt in NJ
Well-known member
That's why I like using the 110volt test light, usually the problem area will smoke and can be found, on starters it is usually fixable with cleaning and some insulating paper/ varnish
The bar to bar test shows weak solder joints, but like you said-- time, I usually resoldered all commutators when I was rebuilding quantities is starters/generator for resale, it was about as quick as checking/ testing
The bar to bar test shows weak solder joints, but like you said-- time, I usually resoldered all commutators when I was rebuilding quantities is starters/generator for resale, it was about as quick as checking/ testing
Keith True
Well-known member
For the most part if the armature has a problem,it is just no-go.Unless it is something rare,or obsolete nobody will pay to have it fixed.About 15 years ago I pulled the starter out of a big Fiat-Allis bulldozer and dropped it at the shop I use.He called me and said the armature was just junk.He had no supplier to get one from,and had determined beyond a doubt it was not something he was going to fix.He doesn't rewind,and we don't even know any small shops that do anymore.He knew of a place to send it,so I sent it to them. had it back in one week,and he put it back together.With shipping it was about $500.for the rewind.Fiat-Allis wanted $3450.for a starter,it was a month away,so this was a bargain to us.