Bench testing a starter

[Mark W.]

Any tips on how to test a starter of a farmall bn? It is still 6 volt.

 

[old]

The common man for the most part can not do a good bench test on one. Yes you can hook it up to a battery and see if it spins over but that will not tell you if it will pull the load of an engine since you can not take a reading of the amp draw it has. Best way to test one is take it in and have it tested at an auto parts store or such as a re-builder type place. Most will do it for free

 

[Geo-TH,In]

Mark,
My farmall C has a 6 v starter, but it's powered by a 12v battery after tractor was converted over to 12v.

I would just use jumper cables and hit it with 12v. May want to have starter held down or put in a vice so it won't jump off bench and land on your foot.

I can't think of how you would load test starter, just see if it spins and starter drive works.

 

[matthies]

Hitting that starter with 12 volts may overspeed it, since there isn't any load on it, have seen it done. You will need a different starter after that.

 

[old]

Funny I have hooked up many 6 volt starter to 12 volts and NEVER ever hurt one yet and that was on the bench

 

[Fatjay]

I use my battery charger, put the starter on the work mate and clamp it in. It spun. Hooked it back up to the tractor and jumped the starter directly, and the engine turned over. Turns out I just had a dead spot on the starter and the teeth were binding.

 

[Ray]

A 12 volt battery will work fine with a 6 volt starter. Most of the old 6 volts have heavier windings than the newer 12 volts. All you need is a resistor for the points and 12 volt light bulbs.

 

[Steve@Advance]

If it's still on the tractor, best test is with an analog volt meter under real life load conditions.

Compare battery post voltage while cranking to voltage from the starter post to ground.

If the battery volts stay high, and the starter post volts are low, below 3 volts, there is a bad connection between the starter and the battery. Could be a cable end, loose connection, bad solenoid/contactor, too small cables.

If battery volts drop to about 3 volts or less, and the engine cranks slow, either the battery is low/bad, or the starter is drawing too many amps. Have the battery fully charged and load tested.

If there is voltage between the starter post and ground, and the starter does nothing, there is a problem in the starter.

If the battery tests good and the problem still exists, open up the starter. The best test for a slow starter is a visual inspection. Look for obvious problems, like broken connections, burned field windings, etc. Check the bushings for wear. If there is evidence of the armature dragging the inside of the field, the bushings need to be replaced. Look at the brushes and commutator. The brushes are worn down to the holder, replace them. The commutator should be clean and bright and all segments the same color. If some are darker or lighter, the starter needs to go in for service.

Most starters can be field repaired without special tools. If it needs shop service, that's typically less expensive than replacing it. Connecting a starter to a battery on the bench proves little, no way to load test it.

 

[UncleTom]

And one more thing on bench testing. I know an old guy (91 now) and still works on starters and gens and alternators. He taught me to clamp the starter in a vice and take a 2x4 and stick in between the bench and bendix while it is running and saw wood with the 2x5 and bendix drive gear. If it wont grind wood and slips the bendix is bad. Old timer, and none better.

 

[Dean]

I agree.

An unloaded series would motor can indeed do that (even at design voltage).

Dean

 

[teddy52food]

Put a channel lock pliers on the gear & you can tell if there is torque there or not.

 

[teddy52food]

Maybe that is why the starter is not working right to begin with. We always wound them up good on the test bench after rebuilding them.

 

[Geo-TH,In]

Old, the difference is you have done it, so have I. While others with no experience hand out advice. BTW, is you are worried, use a lawn mower battery. Hitting an unloaded 12v starter for a second or two won't be the end of the world.

 

[Owen Aaland]

There are specifications for running draw and rpm along with amperage draw for a locked starter.

 

[thdrduck]

An unloaded starter can over speed and centrifugal force can cause the windings to separate, can ruin the armature and stator. Probably wouldn't happen to a 6v starter on 6v, but a 6v on 12 can happen easy.

 

[Owen Aaland]

Starters are self limiting in maximum rpm because as the speed of the armature increases it starts to generate voltage that is in opposition to the battery. At the maximum rpm specs the voltage generated is enough to offset the battery voltage and the armature speed will not increase any further.