It used to be, a feller could take his generator, alternator, or engine starter in to most any decent Auto Parts store and they had a bench test machine setup. Are these any good? I found a place that still has a starter bench tester, but I'm not even sure it's worth the trouble, or whether it will tell me anything useful. Rebuilding a starter is easy peasey to do yerself (they aren't usually very expensive either) but ... crappy store bought "100% Guaranteed Used" starters that soon fail seem to be pretty common these days. This one spins up smooth and fast. I'm almost certain it will work fine. But I don't know for sure. For my part exchanging starters in and out and replacing them till I get a good one isn't part of the plan. The best way or maybe the only real test, is to install it. I'm motivated, but probably not that motivated. Do the bench testers measure the no load current draw and make a determination that way? I assumed the bench testers should load a starter down to simulate engine starting demands, but I don't think that's the case. How about the starter drive or Bendix, do they test function on that?
That's pretty succinct, I guess. Maybe another cup of coffee will get you to open up a bit more? Yeah, I don't think it's worth lugging that thing in.
Most of these parts store testers are only as good as the person operating it. You are better off going to a local rebuilder if you have one.
I don't know what or how they tested them on the bench but when on the car and under load the test was to see how much current it pulled. Maybe a bench test would include a max RPM test also?
"Local" means 150 mile round trip now I guess. I bought a new starter from DB Electrical some time ago, this rebuild is just going on the shelf as a spare so it isn't too important. I just like to know if parts is good, or not.
Ok, let me tell how an older neighbor friend of mine educated me a long time ago. He worked in San Francisco in the 50’s and 60’s at an auto electric shop. My problem, the starter in my ‘59 Chevy quit starting the engine. Worked fine when I used the truck the day before, nothing the next morning. I did all the prereq test. Pulled the starter and ran jumper cables to it, it motored fine, spooled up nice and easy. After putting it back in and pulling it out, musta been the 3rd time, he walked across the street and said “you need to fix that starter”. I said “it works”? “Bring it over” he says. We take it apart, he eye balls things, “well, looks like we could turn the armature, but we can’t “. “Oh, here’s your problem”. He pointed out that maybe 10 or so wires had “black “ around them on the armature. He goes and gets a map torch and an old iron (looked like a 3/8ths square bar ground on the end with a wooden handle). Heats up the iron, heats up a can of solder (solid chunks) and starts dipping and soldering the wires that were not bonded. So after it cools down he sands the armature and we put it back together. He said “now go give it some juice “. So, remember I said it spooled up nice and easy? Now when I hit the voltage to it, it torqued over. I mean so hard and fast it popped the jumper cable off. Before we put it together, he did bring out this HUGE analog bench meter and took maybe 5 or 6 different ohm checks. Anyway, after all the above I have no idea what a “starter tester” would do or tell you, but felt compelled to wear my thumbs out to let you know a starter should not just run, but hit speed near immediately
Interesting story, gives me more to think about. It worked before, brushes look good and replaced recently with plenty of meat. I sanded the armature and replaced the rear bushing.
A modern storage oscilloscope with a current clamp can say a lot about electric equipment. With the starter on an engine you can check the current the starter draws under load. If the brushes, commutator or some winding is bad the current draw will change a lot as the starter rotates - probably going down as connection is lost. (Same test is used on electric fuel pumps.) More commonly it is used to make a relative compression test. As each cylinder compresses the load on the starter goes up, and the current the starter draws also goes up. If it's all the same for all the cylinders they all have the same compression (that's why it's a relative test, it compares the cylinders with each other), if one draws less current that means one cylinder is down on compression. Hook another oscilloscope channel to ignition on cylinder 1 and you can see which cylinder is the one with the issue. A regular compression gauge would find the issue too ofcourse, but it takes far more time to unscrew all plugs and testing all cylinders one by one. (Especially on some modern cars that need to be pulled apart just to reach some of the plugs.) You still may want to use the gauge to verify what the actual compression is, but the scope can tell you if & where there is an issue, so you can dig deeper into it or move on to looking for other problems. Not sure how useful a current test on a new(?) starter running unloaded on the bench would be, supposedly new motors may need some use before the brushes and commutator has worn in and give good contact all the time. But if anyone has access to the equipment a test would be interesting.
When I worked for A-1Auto Electric in Denver, the OldMan would test the Armatures on a machine called a GROWLER.
Do the bench testers measure the no load current draw and make a determination that way? YES I assumed the bench testers should load a starter down to simulate engine starting demands. NO How about the starter drive or Bendix, do they test function on that? YES You pretty much answered your own questions.
A growler test the armature for shorts in the windings to ground. The field coils need to be tested also…usually done with A/C voltage through a light bulb. Very few parts house tester will put a starter under a load. Mostly looking at amperage draw. A starter Bendix or Drive can be tested with a hammer handle applied to the teeth of the drive to see if there is any slippage plus this test can also serve as a poor-man’s load test…[emoji41]
Some starter testers do load the starter somewhat, but not all. An oscilloscope is a great tool to use, but for home use for quick testing (amp) you can use an amp clamp or find a working Vat 40 and you can test it on the car.
I noticed even with no load, an instant 100 amp draw will knock the "surface charge" off a battery right quick, too, ha ha. I know most of the tricks for testing a starter when installed, it's also good to check voltage drop in the cables & connections.
Sanding the commutator will help as long as it's not too worn or out of round. If you have the right equipment it's best to turn the commutator and undercut the mica between the individual commutator bars. The recessed area between the bars fills with material that is worn off the brushes.
I read that, and did that, on the Generator cores I'm working with. A piece of broken hacksaw blade works pretty good for this because it will have a sharp point. The actual saw-teeth are not part of the program in this operation. But I also read, supposably undercutting the mica doesn't apply or is not necessary to Starter armatures, they don't need this operation. Something something about the current involved, they don't get high mica. I don't know if this is really true or not, but agreed with it because it is a pain in the &@$. I know just what kind tasks the new guy gets assigned and you can bet this was one of them.
To do the armature right a guy "should" use and armature lathe so you can true the commutator and then undercut the mica. I've been hunting for a used one for a while but the only one I found the guy who had it thought was gold plated by his asking price. I had to snag this off the net for an earlier show and tell session. Blue is the belt that goes around the piece on the shaft on the motor and around the body of armature .Yellow arrow is pointing at the mica cutter, You have to line up the cutter with each spot and then undercut that section and go to the next one and on around the commutator. Purple is pointing to the lathe bit holder to trim the commutator
I'm still reading pretty much the same "official" consensus as I did a few years ago, generator armatures always get undercut, engine starters don't. I think the claim is that it has to do with the way carbon brushes and generators work, they run constantly of course compared to only intermittently as in a starter, and the brushes by design only wear very slowly. But the problem with a generator commutator the copper bars erode, eventually resulting in high mica. In a starter the brushes are made of a much harder copper material and high mica isn't a problem. They claim undercutting only serves to fill the space with metallic conductive brush material. Hm. Works for me, I'm goin' with that!! With Generators they say to remove any burrs after undercut and then polish the commutator really fine, as smooth as possible after undercutting, and the brushes will last much longer. I found it interesting too that spark chasers have "color charts" for commutator diagnostics, sort of like reading spark plugs, to gauge the health of brushes & commutators.
Yeah, generator brushes are basically carbon and pretty soft. Starter brushes are something like sintered copper, probably because of the high currents involved.
A clampon meter, like the Fluke shown above, are an excellent testing tool. You must buy one that can detect DC as most are AC only. A Fluke is one of the best available.
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