Starter works on bench but doesn't when hooked up on tractor

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Andy M
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Starter works on bench but doesn't when hooked up on tractor

Postby Andy M » Sun Jan 14, 2018 8:16 pm

I have a 1948 6v Cub that I've owned for about 2 years and it worked great until about a year ago. I rebuilt the starter, but it won't turn. I replaced the old battery and checked connections. In addition, I just rebuilt the carburetor because it was all gummed up and leaking. In the process, I tried to check and see if I was getting spark on the plugs when I turned the hand crank, and I wasn't getting anything. I'm not sure what the deal is and I'm not mechanically minded so I could totally be missing something. I'm wondering if there's an issue with the Magneto. I've also read through the forum that it could also be a grounding issue. I want to learn how to fix and repair this awesome tractor and would appreciate any help. Any ideas? Thanks!

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby staninlowerAL » Sun Jan 14, 2018 8:42 pm

Andy, welcome to the Forum. Just a couple of things for you to be aware of:
1. A true magneto system produces it's own electricity and is totally independent of the battery, starter, and all the other electrical equipment on your tractor. There is NO electrical connection from the magneto to the battery. If the engine is turned with either a hand crank or a starter and the magneto is working properly you should get a spark at several different places. Assuming your magneto is OEM and not been modified to use an external coil then that's the problem to address before you can get it to start. If you have an external coil with your magneto then the above statements are different. Prime the oil pump also before trying to start the engine.
2. You said the starter works on the bench but not on the tractor. That is probably a contact issue, either positive or negative or both. Check and re-check the wires, starter switch and grounding. The starter is grounded by the bolts that hold it to the bell housing so everything has to be shiny bright clean to work well.
3. One more post and you can access the manuals at Quick Links tab (top left corner of this page) and download all the manuals that you will need to work on and understand your Cub. Especially get the GSS 1012 Electrical Equipment which explains in detail how to service and maintain both the battery and magento type ignition systems. Good Luck and post back on what you find. Stan

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Eugene » Sun Jan 14, 2018 10:08 pm

Andy M wrote:I rebuilt the starter, but it won't turn.
Explain. It won't turn. Is that when bench tested or when installed in the tractor?

It will take 150 amps to start/turnover the Cub's engine with starter when installed in the tractor and 75 amps for bench testing. You won't be able do that with most battery chargers.
I have an excuse. CRS.

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby BigBill » Sun Jan 14, 2018 10:33 pm

Don’t forget these old 6 volt systems are positive grounds.
I'm technically misunderstood at times i guess its been this way my whole life so why should it change now.

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Barnyard » Sun Jan 14, 2018 10:49 pm

BigBill wrote:Don’t forget these old 6 volt systems are positive grounds.

The started doesn't know that and will start either way. However if backwards you will have charging problems.
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Andy M
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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Andy M » Sun Jan 14, 2018 11:11 pm

Eugene wrote:
Andy M wrote:I rebuilt the starter, but it won't turn.
Explain. It won't turn. Is that when bench tested or when installed in the tractor?

It will take 150 amps to start/turnover the Cub's engine with starter when installed in the tractor and 75 amps for bench testing. You won't be able do that with most battery chargers.


It was turning on the bench. After I put it back on the tractor and hooked everything back up and pulled on my starter, I got nothing. Will check my contacts and make sure they're polished and clean :D

Andy M
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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Andy M » Sun Jan 14, 2018 11:18 pm

staninlowerAL wrote:Andy, welcome to the Forum. Just a couple of things for you to be aware of:
1. A true magneto system produces it's own electricity and is totally independent of the battery, starter, and all the other electrical equipment on your tractor. There is NO electrical connection from the magneto to the battery. If the engine is turned with either a hand crank or a starter and the magneto is working properly you should get a spark at several different places. Assuming your magneto is OEM and not been modified to use an external coil then that's the problem to address before you can get it to start. If you have an external coil with your magneto then the above statements are different. Prime the oil pump also before trying to start the engine.
2. You said the starter works on the bench but not on the tractor. That is probably a contact issue, either positive or negative or both. Check and re-check the wires, starter switch and grounding. The starter is grounded by the bolts that hold it to the bell housing so everything has to be shiny bright clean to work well.
3. One more post and you can access the manuals at Quick Links tab (top left corner of this page) and download all the manuals that you will need to work on and understand your Cub. Especially get the GSS 1012 Electrical Equipment which explains in detail how to service and maintain both the battery and magento type ignition systems. Good Luck and post back on what you find. Stan


Thanks Stan!

1. I think I understand the function of the Mag well enough that what you said makes sense to me---there's no external coil on it. You clarified my point in mentioning the Mag was because I wasn't getting any spark when I hand cranked my Cub. My thought that was that I could spend a lot of time trying to troubleshoot my electric starter, yet still not get the engine to fire up if I have no spark.

2. I'll go back and try to clean everything up. Last year, I thought I had a bad starter switch but I replaced that and have still obviously had issues.

3. I'll check those resources out and see if I can fumble my way through this.

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby k hutchins » Mon Jan 15, 2018 7:19 am

As far as the mag goes l would test the coil before condemning the whole mag. The coil is the easiest part of the mag to change out (besides points, condensor, and rotor).
If it were me that's where l'd start, and while l had it apart l'd change out the other components as well. Then if no spark, l'd start digging deeper.

Just my FWIW
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Re: Starter works on bench but doesn't when hooked up on tractor

Postby staninlowerAL » Mon Jan 15, 2018 9:07 am

Andy, one reason I referenced the manual is there are other parts that k hutchins listed that must be working right also. Examples: rotor and pinion gear, spark advance. The manual will help you understand the overall workings of the magneto. If you get that deep, there's a special tool required to disassemble it so as not to damage anything. And it has to be timed correctly. Good Luck.

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Landreo » Mon Jan 15, 2018 9:14 am

For your magneto, I would not change the coil unless it is verified to be bad, that is the most expensive part. I would just clean or file the points first.

For the starter, check the battery cable and battery ground for good contact, check the same on the starter, check the mechnical connection of the starter rod, is it binding in someway that prevents closing of the starter switch. If all is good and there is no click of the starter then I would take the starter off and remove the starter switch top and look in there for corrosion.

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby ScottyD'sdad » Mon Jan 15, 2018 9:18 am

Try the starter, with jumper cables, while on the tractor. If it turns, you have a wiring isue, or ground issue, somewhere between the starter an battery.
Starter grounds through the starter housing, where it goes into the bell housing. Be sure that area is clean.
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Andy M
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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Andy M » Mon Jan 15, 2018 5:18 pm

After reviewing the previous comments, I decided to first try and see if I could get the starter to work on the tractor. Here are my results from tinkering on the Cub today for a couple hours...

Went through and tested some wiring systems...
1. Tested battery and it is fully charged and reading at nearly 7.0V on meter
2. Tested battery ground by testing voltage through negative battery post to a bolt on the starter and read nearly 7.0V
3. Tested battery cable by testing the voltage from the positive battery post to starter switch, which read nearly 7.0V
4. With the ignition switch on, I tried to get starter to run by connecting a negative jumper from the negative post to starter switch---had a spark and a click and nothing else.
5. I then took off the starter switch and starter, disconnected them and cleaned up the connections and then reassembled and made sure the switch had good contact with the starter post.
6. I reinstalled the starter and the switch and reconnected the battery and tried the starter again. This time, I got some action! The starter turned, but very slowly. I thought it might take off and I held the switch and the starter kept running for about 5 more seconds. I let go for a moment and then pulled on the starter again with similar results---a very slow turn. I let go again and on the third time (maybe it was the fourth--I can't quite remember), the starter wouldn't turn.

And those are the results from my tinkering this afternoon. Anybody have any thoughts on what might be going on? Why the slow turn?

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby SONNY » Mon Jan 15, 2018 5:34 pm

Bad field coils or armature.--is armature shiny? brushes new/clean? bushings worn? This does affect performance.---since you have mag ign.--leave your 6 disconnected from starter and jump with 12 and see if it still drags.---I am thinking your starter is worn out like most of my old ones.---Would almost look like time for a new starter.--looks like you did all the tests. thanks; sonny
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Re: Starter works on bench but doesn't when hooked up on tractor

Postby staninlowerAL » Mon Jan 15, 2018 5:37 pm

Are your starter cables small automotive type? 6v needs the larger cables, I think it #2AWG. Small diameter wire makes the starter turn slower.

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Re: Starter works on bench but doesn't when hooked up on tractor

Postby Landreo » Mon Jan 15, 2018 7:42 pm

Assuming the cables are large enough and the engine itself turns free, I would take the starter apart and check everything once again. Make sure the brushes move freely and the springs are strong. Make sure the starter can be turned easily by hand and there is no binding. Look for loose wires on the inside end of the terminals, etc...


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