How do I test a starter motor? - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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post #1 of 22 Old 07-23-2018, 11:13 AM Thread Starter
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How do I test a starter motor?

My JD4100 was starting fine 4 days ago. This morning it only clicked like Ihad a dead battery. While I had the battery removed and on the charger I used a jumper cable and my pickup truck. The tractor seems to be more responsive when I turn the key to "ON" but when I turn the key to "START" the engine turns over only 1/2 turn and stops. I need to see if the problem is the starter but I don't know how. I could purchase a new starter just to see if that's the problem but I would like to check things out better before driving 40 miles to the JD store. Can someone give me advice? Thanks.

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post #2 of 22 Old 07-23-2018, 11:26 AM
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Re: How do I test a starter motor?

Get your battery load tested before anything else.
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post #3 of 22 Old 07-23-2018, 11:43 AM
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Re: How do I test a starter motor?

Never owned a JD but here goes.

Use your jumper cables. Neg on the engine, bracket, ect. Not the battery neg post. ( Get to that later. ) Touch the pos end of the cable on the starters pos lug. Where the large red wire attaches to it. If it spins over good. It's not the starter. You just by-passed the battery Pos & Neg connections and Starter relay.

You should have a starter relay. They sometimes go bad internally. burning the internal contacs. Follow the starters large red wire to it. Take a screwdriver and on the lugs of the relay were the 2 large wires go to it, put it between the 2 posts. Pivot the screwdriver to connect the 2 "/, Starter should turn over if the battery connections are good. I don't think your ignition switch is bad as it operates the starter relay.

You could have a poor ground, Battery neg post or where it attaches to the frame.

I just had the same problem on my 1650 Cub. Turned out the battery cable end clamps I put on years ago. Universal type. Behind the C part, you loosten 2 bolts. Put the wire under a plate and tighten. The connection was all corroded. On both Pos & Neg.
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post #4 of 22 Old 07-23-2018, 12:34 PM Thread Starter
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Thanks Bill. The battery in my truck is in excellent condition but I do plan to do a load test on the tractor battery.

JD 4100 compact Kubota L2050 Kubota BX1500
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post #5 of 22 Old 07-23-2018, 02:44 PM
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Re: How do I test a starter motor?

I repeat what Bill Kapern above said. Do that first. 8' long battery cables have a large voltage drop. Your starter may not spin with that much loss of voltage. Consider why they put the battery on the same side as the starter in most older rear-wheel drive automobiles. There needs to be a battery near the starter.
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post #6 of 22 Old 07-23-2018, 02:51 PM
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Re: How do I test a starter motor?

It would be great if you posted the model number of your engine. Many of us who know engines haven't the faintest idea what engine a JD4100 has (nor care)

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post #7 of 22 Old 07-28-2018, 08:10 AM Thread Starter
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Thanks for all the ideas everyone. I tested my battery under a load - passed the ok. Bench tested the starter motor - Good results. Bench tested the solenoid - tested ok - but wait, what's that sound?
I found that when the solenoid was fully engaged and the high current contacts closed these was a sizzling nose inside. The contacts were burnt and the engine would turn over only for 2 or 3 seconds and stop. When the contacts cooled and I tried to start it again it would do the same thing each time. I finally found a replacement solenoid and no it's good to go.

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post #8 of 22 Old 07-28-2018, 09:07 AM
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Re: How do I test a starter motor?

Quote:
Originally Posted by Square Dude View Post
I repeat what Bill Kapern above said. Do that first. 8' long battery cables have a large voltage drop. Your starter may not spin with that much loss of voltage. Consider why they put the battery on the same side as the starter in most older rear-wheel drive automobiles. There needs to be a battery near the starter.
Then why do 8' jumper cables work to jump a vehicle that has a dead battery? When you jump start a car, you connect to the battery, so you're adding the length of the jumper cables to the length of the original battery cables in the vehicle to get to the starter and it still turns the starter. A good pair of 0 or 00 gauge jumper cables connecting a good strong battery directly to a starter should be able to turn any starter that's in good enough shape to turn.

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post #9 of 22 Old 07-28-2018, 09:27 AM
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Re: How do I test a starter motor?

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Originally Posted by Nouveau Redneck View Post
Then why do 8' jumper cables work to jump a vehicle that has a dead battery? When you jump start a car, you connect to the battery, so you're adding the length of the jumper cables to the length of the original battery cables in the vehicle to get to the starter and it still turns the starter. A good pair of 0 or 00 gauge jumper cables connecting a good strong battery directly to a starter should be able to turn any starter that's in good enough shape to turn.

Because the battery isn't dead, but just low, and needs a bit of "help".
If it were truly dead, it'd suck the booster battery down to near nothing.
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post #10 of 22 Old 07-28-2018, 09:40 AM
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Re: How do I test a starter motor?

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Originally Posted by Bill Kapaun View Post
Because the battery isn't dead, but just low, and needs a bit of "help".
If it were truly dead, it'd suck the booster battery down to near nothing.
Not only that, but when boosting a battery...you are typically using a vehicle with the engine running...which means that the "donor" battery is being charged while "helping"...not just getting drained down as it helps

Also...a faulty battery can be fully charged one moment and lose its entire charge in a moment...which is why load testing is so critical to determining a battery's usefulness...a digital load tester is available on ebay for a little less than 30 bucks ...and a very handy tool to have around...good luck with it
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post #11 of 22 Old 07-28-2018, 12:11 PM
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Re: How do I test a starter motor?

Boogity. Glad you found the problem. Screwdriver across the relays main lugs would perhaps of narrowed it down sooner? Key in start, ohm test for high resistance between the lugs when it was energized. Or if preferred, a voltage drop test.

My original post on using jumper cables to trouble shoot. I never mentioned to use them connected up to a vehicle to use that way. Instead of using the jumpers on the tractors battery to do it. Because I thought it didn't need to be said. You knew how to do it on jumping in the 1st place. .

I was trying to talk you thru without taking things off. ( Initally By-passing the battery. ) To test with the cables. Save you some work.

Nouveau Redneck, I read it as more of a statement than a Q on "why"? If a question, Bill Kapaun's and Mark's reply are spot on, concise.

My MG's have the battery located behind the seat in a battery box. I've seen some ppl put them in the trunk. As you said, good cables. Normally a jumper cable has size 8 or 6. 6 being larger. The size of the wire carry's the amps demand going thru the wire, without melting the wire. Who cares how long they are if the connections are good. They work, eh? No voltage drop.

Last edited by locodave64; 07-28-2018 at 12:20 PM.
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post #12 of 22 Old 07-28-2018, 12:32 PM
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Re: How do I test a starter motor?

My Two Cents: I've had two units, and tractor, and a boat, that I thought had bad starters. As it turned out, NEITHER starter was bad. The tractor? Safety interlock switches came apart all by themselves. The boat? Battery cable corroded in the salt climate, and looked like it was cut all the way through. Could not easily see the damaged area, but an engine guy found it in under 30 seconds.

So, test your starter the cheap and easy way: Take it out of your tractor. Hook it up directly to jumper cables and your CAR. If the Bendix drive kicks out, you know the starter is good. Look for other problems.

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post #13 of 22 Old 07-28-2018, 04:01 PM
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Re: How do I test a starter motor?

Hotajax, Yuppers been there and have the shirt to go with. You can look at everything.

1st time I did it, I didn't hold the starter tight to the ground. I did it more to watch the bendix drive kick out. Motor was mounted on the engine my 1st try. Jumper to the large lug. Motor spun kinda slower then normal. It didn't engauge the flywheel.

Took it out. Those things have a mean kick when you hold it down on the ground. Touch the go post with the pos cable end. I'm talking about an automobile starter. Haven't try'd a tractor starter -> yet. Basicly the same.

On boats, I owned a 17ft I/O Merc open bow run about for around 10 years. The best times on owning one is 1st when you buy it. Then when you sell it.
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post #14 of 22 Old 07-28-2018, 06:05 PM
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Re: How do I test a starter motor?

I'm happy you found the problem with your starter Boogity. Great job.

I like to have a systematic way to trouble-shoot. When looking into a starting problem like yours I like to make dead sure that the battery is OK first. How many times someone has stated up front, first thing, that the battery is A-OK. Finally you read that the battery was 13 years old!!! Looking at battery connections and load testing the battery should be first items on the list. In the absence of a good carbon pile battery load tester (which truly load tests the battery) one can place a DC voltmeter on the battery and observe the reading while attempting to crank the engine. The starter has to attempt to turn. The voltmeter should not drop below 10 volts. If it falls to something like 2 volts or anything less then 10 volts the battery is probably toast. You've just load tested the battery.

I have a set of battery cables that are at least the length of a pick-up truck. They are very heavy constructed. They will jump start most any vehicle with a drained battery. In these situations the jumper vehicle battery is assisting the dead vehicles battery. If the dead vehicle battery is truly defective, open, sulfated, about to blow up in someone's face, and is just a plastic box not willing to assist in any way then in most cases the jumper battery won't start the dead vehicle. In older vehicles (1970 - 1990 or so) some domestic vehicles needed near 200 amps from the battery to start. That will draw a strong battery down to about 10 volts. Most car engines today are 3, 4 or 6 cylinder and the starters are new gear reduction design that draw less current. It is not necessary to crank today's cars for 10 minutes to start them on a cold morning. Fuel injection!

The only older domestic car I remember where the battery wasn't on the same side as the starter was the Chevette - one of GM's forgettable "jewels".

Good work. I'm glad you got it working and without shorting out anything or replacing perfectly good parts.
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post #15 of 22 Old 07-29-2018, 09:36 AM
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Re: How do I test a starter motor?

Quote:
Originally Posted by Bill Kapaun View Post
Because the battery isn't dead, but just low, and needs a bit of "help".
If it were truly dead, it'd suck the booster battery down to near nothing.
First off, he said he was hearing a click, which is the same symptom on a car when the battery is low, not so dead that it will short the boosting battery.

Secondly, the recommendation was to use jumper cables to jump directly to the starter, which will bypass the battery in the tractor and it will have no chance to draw down the jumping battery.

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You know you might be a Nouveau Redneck if...
1. You use the cup holder on your tractor to hold your cosmopolitan instead of a beer
2. Your "Santa on a tractor" Christmas yard decoration is actually a high tech digital hologram.
3. Your deer camp cuisine is better than most 3 star restaurants.

Last edited by Nouveau Redneck; 07-29-2018 at 09:41 AM.
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