4020 24V starter bendix disaster

Good afternoon folks,
I have a 64 JD 4020 Diesel tractor. I had a starter issue about two years ago that resulted in me replacing the starter with a reman unit. It worked great up until this winter when I decided to solve a slow battery discharge issue by installing ground disconnect switches for my batteries. After installing the switches the tractor ran great for about two weeks (this is my daily to every couple days cow feeding/snow pushing tractor).

Just before Christmas, I went to plug in my tank heater to get the tractor ready to start later in the afternoon, and my daughter alerted me about 20 minutes later to the fact that my tractor was on fire! Thankfully it wasn't actually on fire, but the right side battery was sparking and flaming like mad. I unhooked the ground disconnects stopped the craziness.

I removed the ground disconnect switches (I used the blade style that goes right on the battery) and tried to reconnect the ground straps directly. The tractor immediately tried to crank without me touching the ignition switch! A lot of aggravation then ensued and after a new set of batteries, new ignition switch, new starter solenoid, and a very expensive JD mobile mechanic bill, I determined that the starter was the problem and I replaced it.

The new (another reman) starter worked great for about two more weeks of work. One morning I went to start the tractor and instead of starting, a terrible crashing grinding noise eminated from the starter and then only the starter motor would spin (no engaging of the bendix or cranking of the tractor). I pulled the starter and to my shock found that the end bearing for the armature/bendix was completely destroyed- grease everywhere, and bits of shattered gear parts distributed all over. I took the starter back to the reman and they warrantied it out- we all assumed there was just an issue with the new bendix.

I charged up my brand new batteries, brought the new starter home, bolted it on, and when I turned the key first there was no activation of bendix- the starter spun, but didn't engage the tractor. I turned the key off, tried again, and this time an aweful "clunk" happened. I pulled the starter again and the gear on the bendix is cracked to smithereens.

I called the reman- they won't replace it again, said the problem is on my end.

I took it into a local shop, it bench tests fine.

I checked to see if my engine is seized up and the motor turns over with minimal difficulty.

After some research,

I took it into a local shop, it bench tests fine.

I checked to see if my engine is seized up and the motor turns over with minimal difficulty.

I checked the number of gears on the starter- worrying maybe I have a gasoline version by accident. Nope- 10 gears (or what remains of them).

Another edit- A diesel mechanic friend recommended I check the flywheel to make sure I wasn't missing any teeth. I didn't see any gaps when I turned it around manually.

My JD mechanic is stumped, his suggestion is to switch it over to 12 volts now that I have to buy a new starter anyway.

I don't disagree with him, but I'm worried there's something I'm missing. I don't want to just put on more parts and have the new 12v starter give me the same issue.

If you've read this far, you have my sincere thanks! I'm all ears to hear the collective wisdom from this forum that I've so appreciated over the years. Trial and error...

Benjamin

This post was edited by farmerben on 01/04/2022 at 04:47 pm.

If I'm reading this right, maybe the starter problem is caused by a worn ring gear. I don't think your mechanic is diagnosing it correctly. What's causing the short and the ruined Bendix?
Check your ring gear, circuits, wiring and continuity. Having him tell you to just convert to 12 volts is an easy answer without him understanding what caused the problem in the first
place. Also, be careful of reman 24 volt components. Better to take your known starters and generators/alternators to a GOOD starter shop and tell them, This is 24 volts! Fix it. Do you
understand?

I'm thinking two different problems and one is the ring gear as you have indicated. The battery must be a short for some reason.

Is there a minimum height acceptable for the ring gear teeth? I can see them clearly through the starter hole. I turned the engine over by hand while inspecting the ring gear for broken teeth and although there weren't any missing I'd wondered about the idea of too much wear and tear and the new bendix teeth not engaging properly. Although this doesn't seem to explain why my last reman lasted a couple weeks before the starter gear exploded.

Thanks for your reply.

Benjamin

As an update and further question (for anyone)- I spoke to another old time tractor mechanic and he was speculating that I might need either a shim for my starter, or the solenoid might need to be adjusted. I'm going to measure the distance from the extended bendix gear to the mounting flange and compare that to the distance from the ring gear to the mounting surface of the clutch housing and see if they match. I did notice that the fly wheel has an odd scalloping of metal scuffed off adjacent to each tooth, I wonder if he's on to something? Have any of you seen shims used for 4020 starters?

Benjamin

Flywheel came loose ?

When you get your new starter remove the
solenoid and run the bendex by hand to see
if it moves free. And for a shim I have
used a gasket from a quad or synchro 30 or
40 series.

If for some reason you decide to convert to 12 volt I am
really happy with the conversion kit I bought from yesterdays tractor parts. Never had any problems since converting. Still have
every thing to change it back to 24 volt.

I had a similar issue with a 720 gas. After replacing a well worn starter drive with a after market drive it would make a more then normal gear noise when starting and after a few starts it would split the gear on the starter drive. After careful examination I discovered that the gear on the replacement drive had teeth of a different pitch then the flywheel. It would go together but as you rotated it around the flywheel it would get tight. Okay I know this sounds like I am crazy but I saw it with my own eyes. A replacement drive from John Deere fixed the issue.

Unless I don't know that I understand what you mean, I don't think the flywheel is loose. It's still turning, and the whole engine turns over with it. There's nothing loose about the ring gear via the starter hole- I can't wiggle anything at least.

If there's something else I should check let me know.

Benjamin

I been reading all the post and there is some good / correct information. I have seen this happen many times. It is a multi problem event. If the
ring gear teeth has sharp raised edges on top / corner of teeth diameter this will hold the starter pinion gear into ring gear while cranking and
keep it from returning to home position after a starting event. When pinion gear is held engaged with flywheel rotation it will keep solenoid
switch turned on and both engine and starter are running locked together with engine running, destroying a perfect good starter. First thing to
fix is replace the ring gear. Next thing to check / monitor is that starter is not staying engaged because of electrical reasons / problems, that
may have damaged the ring gear in first place?? What I have seen is a leak / short to ground on the yellow / starter engage circuit. This short
to ground creates 12 volt path from solenoid to frame to hold the 24 volt solenoid engaged with 12 volt. The 12 volt short is / may not be enough
to pull the solenoid in but, hold solenoid in / engaged after pulled in by its normal 24 volt command. Check this circuit for short to frame
ground. This can be a wire touching frame or a failed neutral start switch shorted to ground. This circuit can not be shorted to frame ground.
Easy to test with a ohm meter. DW

https://drive.google.com/file/d/176EYhNzicKPZCEv1jJEcu0ZveIh53_ua/view?usp=sharing

This is a pretty good representation of the bad areas. I recorded a video of the whole flywheel while I turned it by hand. I didn't realize there were two regions, each about 6-8 inches long, that clearly have more damage to the forward edges of the teeth than the others. I'm assuming this is enough to cause the bendix to ride up in a strange fashion and snap the little teeth?

Benjamin

This post was edited by farmerben on 01/05/2022 at 03:46 pm.

Hi WTW,
Thanks for your response. As I mentioned in my other post with the picture, I took a video of the flywheel while turning it all the way around. I think you've got the problem pinned- unfortunately it looks like I'm looking at a new flywheel. My question for you, is if after I switch out the flywheel, I convert the tractor to 12v, will this likely delete the issue you mentioned with the ground?

Benjamin

This post was edited by farmerben on 01/05/2022 at 03:57 pm.

It also looks to me like the bendix is smacking the back side of the flywheel past the ring gear. Like the bendix is traveling too far (deep).
???

I agree with you, jd2cylman,
But the current starter seems (seemed) to insert where it was supposed to- when I measured the distance from ring gear to the mounting surface it matches what I measured on the fully extended bendix gear. I think maybe one of the previous starters was doing this.

Benjamin

This post was edited by farmerben on 01/05/2022 at 05:59 pm.

The ring gear can be replaced without replacing flywheel . You do not have to replace flywheel. Not hard to
replace ring gear once flywheel is off. I there is a short to ground in energize circuit you will want to
fix it. Nothing wrong with a 24 volt system if you are smart enough to work on them. DW