Electrnic hand growler to test electrical armature with green and red indicator

Measuring across the commutator opposites is a rough check - if each pair has the same resistance it is probably good but even then there are no guarantees. I have never seen the armature resistance stated for any motor though that doesn't mean such figures don't exist.

It would seem logical that each pair should be isolated but that generally is not how the armature is wired and each commutator segment is the termination of two coils.

In reality there is only three ways to test an armature - either build it into a motor and see if it performs ok, use an automated motor fault analysis machine or one of the dedicated armature testers such as an armature growler.

Check that the battery terminals and posts are shiny clean and tight. Check for tight cables on the starter motor. This problem is an indication of a dry joint in the armature of the starter and the only way to check is to remove the starter and have an accredited auto electrician test the armature on a specific piece of test equipment called a "growler"

It sounds like the armature is bad. It should have an even dark ring around the bars of the armature commutator where the brushes ride. If one or two of the bars is discolored above and/or below that it could easily be bad. It could also be pitted between a couple of bars. Normally the space between the bars is even all the way around and nice and "clean cut" looking. If you have access to an armature growler you can test the armature. Hope that helps.

To fully test the armature you need to remove it and use a bit of kit called a 'growler'. Most powertool service shops (especially manufacturer approved ones) will have one of these. You can get a fair idea form a couple of visual inspections too though.
It is best to remove the motor housing so you can see the rear of the armature clearly (the commutator). First of all though, before you completely remove the motor housing you will need to remove the brushes. The running faces of the brushes should be nice and smooth, if they are pitted and and rough looking across the entire running face then this shows that the motor has been sparking too much and the armature is most likely to be faulty. If the running faces of them is only pitted and dull halfway across this would indicate that the field coil is faulty and would need replacing. Once you have checked this, if you want to double check the armature, you should continue to remove the motor housing. the field coil will usually stay inside the housing when you remove it which is good as it means you don't have to disconnect any wires. You need to visually inspect the copper segments at the end of the armature (the commutator). All the segments should be of a similar colour and not too dark, although there will be carbon 'burnt' onto them. The gaps between each segment should be pretty much straight and all the same between each bar. If an armature is shorting out you will normally find a couple f the segments have started to raise slightly. These segments will have an abnormal gap between them and be darker or appear mire burned than the others. If they all seem fine, the only other check you can do on an armature is with a growler so you would have to get in touch with your nearest repair shop and see if they can help you.

it is very possible that the problem is in the starter motor itself
the commutator bars on the armature are soldered onto the armature windings and is is reasonably common that the solder becomes what is known as a dry joint
this is manifested when the armature stops spinning and such a bar ends up under a brush thereby breaking the circuit
if the brush is across the gap then the next bar can start the armature spinning but a problem such as what you describe indicates a problem starter motor
remove the starter and have it bench tested , pulled down and inspected and armature growler tested for faults by an accredited auto electrician professioanl
if it proves to be a good unit then it could be relay or ground wire problems

There could be an issue with the oil sending unit, spark plug boot or faulty on/off switch. Easy tests. Always use a new plug for testing. Unplug the oil sending unit wire and retest for spark. If spark may need to change the oil or low oil. If still no spark, leave the sending unit wire unplugged and remove the boot from the plug wire. Insert a short piece of paper clip wire into the end of the plug wire and hold near metal of the engine for test. If spark, replace boot. If still no spark, unplug wire from on/off switch and retest. If still no spark suspect faulty coil ~ redo all tests using old coil. If still no joy return new coil for exchange. I use a growler to test coils(growler used for testing armature for short, place one leg of coil on each pad of growler and activate growler for short burst). Good luck.

Always have a new spark plug handy to determine if faulty plug when no or weak spark. If your engine has an oil alert, disconnect sensor wire and re-test. If still no spark suspect spark plug boot or coil. New or used coils are available at small engine repair shop. If you have access to growler (used for testing armature), by placing coil on growler with one leg on each pad, you can test coil for signs of life. Good luck

I have model MT323A snap on growler, any idea what it might be worth? Thanks!

Mike

More than likely you have a worn brush. If the breaker was running good and then just stopped this is the case. These brushes have a pop-off feature that will stop the motor when it is time to replace the brushes. If you replace the brushes and are getting a lot of sparking, the armature or field more than likely may have a short. Sometimes its the armature, sometimes it's the field, and sometimes its both (running short). You have to have a short tester and a growler in order to test for the shorts. One thing to look for is any burn marks on the windings of the armature, and look for scarring on the inside of the field which may have gotten damage due to rubbing from the armature. An imbalance in the electrical field can push the armature into the side of the field while it spins.

Hi, You need a Growler.
http://en.wikipedia.org/wiki/Growler_(electrical_device)