The Stovebolt Site Forums The Shop Area The Electrical Bay Need starter help - How to test an armature?

My ‘48 Chevy 3600 has a 235 engine swapped into
it and has been converted to 12V by a PO, but it still has a 6-volt starter.

I’m having an issue with getting the starter to work. I believe the starter is internally shorted through the armature.

A few days ago, while reinstalling the starter and connecting the positive lead, the internal parts of the starter switch shifted and caused a short which shorted my battery through the case of the starter directly to ground. I shorted it a handful of times trying to figure out where the issue was. After figuring out that the switch was bad I replaced it with a NOS unit, and I verified that the NOS switch does not short on my starter.

The issue I am having now is that the starter simply does nothing. When I hook it up and turn keyed power on, the truck’s fuel gauge pins to full (the gauge is inop and usually stays in the full position) and when I push the starter switch in that gauge drops down to empty (where it usually sits with keyed power off) until I release the starter switch, leading me to believe that there is a short in the starter and not an issue with it getting power.

I have verified that my battery is good and tried switching batteries, my positive and negative connections are both clean. There is no short through the starter switch and no short when the switch is not closed (engaged).

I pulled the starter apart and have found no obvious defects or visual evidence of shorts.
I’ve been trying to test the armature but I am not 100% sure that I’m testing it correctly. I don’t have access to a growler, just my multimeter.
There is not a short from anywhere on the commutator to the iron core or shaft. However, every section of the commutator has continuity and 0 ohms of resistance to every other section, which leads me to believe there’s an internal short.

Does it sound like I’ve correctly diagnosed the issue?

Also, if I’m correct, what is my best bet for sourcing a replacement armature? Or is it something I can rebuild myself if I buy the correct tools?

T.M. - Have you tried to test the armature using "Steps 1 and 2" as shown on Page 12-22 of the 1948-51 Chevy Truck Shop manual.

Done with a multimeter (deosn't require the growler), you can at least get a preliminary indication if the armature is grounded or not.

A little digging in some Chevy Master Parts Books shows the armature was listed under two different GM#s over the years:

GM# 1867897 Armature, 6V 1938-50 for ALL 6 cylinders

GM# 1917855 Armature, 6V 1938-55.1 for ALL 6 cylinders (this number became active in 1951, replacing the original part number)

This armature is actually the same one used in 6V GMC and many GM passenger car 6V application too.

A quick scan through the web located just one supposedly Vintage 1940 1950 NOS Delco Remy Chevrolet GM Starter Motor Armature 1917855, but it looks to be in pretty rough condition. I also found a listing for a 5040-1700 Reman Armature for Delco 10MT Starters 6V CW Straight Spline which would provide you a warrantied replacement armature if that's the way you want to go.

Hope this is of some help answering your questions.

Thank you. I haven’t seen that manual before.
I believe I did those checks already, but I’ll double check tonight.

Thanks for the part numbers too. That’ll be very helpful.

Since all the commutator bars are connected to each other through the armature windings, a reading of zero ohms between any two commutator bars is normal. The only way to test for an internal defect is with a growler. At least it's been that way in the 65+ years I've spent repairing starters and generators. Make sure BOTH ends of the battery cables are clean and tight. Even a slightly dirty connector can create enough resistance to create the "no run" condition you're describing. Try removing the new foot start switch and touching the hot cable directly to the copper lug on the starter housing- - - - -that should cause the armature to spin without engaging the drive gear into the flywheel. If that doesn't happen, check the brushes for proper contact with the armature.
Jerry

Ok, I was able to work on it tonight and got it working...for a bit, then it failed on me again.

I first did as many of the tests as I could on the starter in accordance with the shop manual. Everything I could check tested good.

I cleaned all of the mounting surfaces up in case there was a grounding issue, re-seated the brushes to the commutator with some sandpaper, and cleaned off the battery cables and mounting surfaces on the battery and starter for the 100th time just to be safe.
One of the brushes was pushed down a bit (forward on the starter with said starter installed) so I pushed it back to its correct place. It had a sizeable ridge built up where 1/8 of it was riding off of the side of the commutator, so I filed it down before reseating all of the brushes with 80-grit then 400-grit sandpaper.

One thing I noticed is that the wires that connect the field to the brushes float pretty close to the starter case and they'll cause a short. I was careful to install them so they didn't contact the starter case and check it with a multimeter after the starter was completely rebuilt to ensure there wasn't a short between those wires and the case.

I "bench-tested" (On the floor for me) the starter using a spare battery and leads per @Hotrod Lincoln's suggestion - thanks - and it worked.
So I reinstalled it in the truck and tried it, and it worked at first! I got about 30-seconds (non-consecutively) of starter action but on the last start attempt when I let my foot off of the pedal the starter coasted to a stop and has refused to make any movement since then. Bah humbug!

I've heard that armatures can have a "dead spot" of sorts and won't do anything if the starter is turned a certain way. That is my first suspicion for my starter. Tomorrow I'm going to pull the starter just enough to spin it a bit and see if that'll let the starter do its job again. This seems like the most likely issue to me since the starter only stopped working after I let off of the pedal and it came to a stop naturally. I don't have access to a growler, so unfortunately I can't test the armature any further.

If that doesn't work I'll probably check on those field-to-brush wires.

There's a way to spin the starter a little without unbolting it. Disconnect one battery cable- - - - -doesn't matter which one- - - -put the transmission in high gear, and have someone hold the starter pedal engaged while you rock the vehicle backwards. The flywheel moving opposite its normal direction of travel will spin the starter armature to a different position. The reason for disconnecting a cable is to prevent the starter from suddenly taking off in case you're right about the armature having a dead area. Then replace the cable and try cranking the engine. If that works, yes, you need another armature! It might be possible to do the same thing by disabling the battery, trans in neutral, holding the start pedal down, and pulling on the fan blades to turn the crankshaft backwards- - - - -CCW from the front.
Jerry

Whoops, forgot to update this thread.

I tried turning the starter to another position but it didn't do a thing so I pulled the whole starter and successfully tried it on the floor. I also visually inspected the field-to-brush wires but didn't see any evidence of a short. The starter worked fine on the floor, so I figured I'd toss it back in the truck. Since floor-starting it put a little bit of slag on the copper lug on the starter housing, I cleaned it up with sandpaper instead of just scotchbrite, and I think that may have been just what it needed. The starter worked just fine when it went back in the truck and has worked fine for the past 15-ish start attempts now.

Great to hear you found a solution and things are headed in the right direction. Thanks for reporting back.