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Damage flywheel ring gear

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montymech View Drop Down
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    Posted: 12 Aug. 2016 at 8:09am
This is the flywheel out of my CJ3A. There is a six inch length of teeth that is almost destroyed whilst the remainder is almost intact. I have never seen flywheel damage so localized. Is this Willys normal or has this been caused by over heating on assembly perhaps. Or is it a cheap import?
Interestingly, when I ordered a new ring gear the 97 tooth count appeared listed non CJ3A. The starter has 9 teeth. The clutch/ flywheel assembly  was all very clean as though someone had been in there recently
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Izzy Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug. 2016 at 9:02am
I believe it is the most common area for the starter to engage.

Almost always one cylinder has more compression than another. Therefore the engine tends to stop in same location.

As for the wear. Poor batteries as well as wrong fit up of parts or worn bearings can cause the wear you are seeing. Oh and a poor flywheel (out of round) could cause this.

I suggest that you rotate to good section and install starter. Then manually pry the Bendix into engage ment yo see about the 9tooth vs 97 tooth.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote rocketeer Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug. 2016 at 12:31pm
The 97 tooth flywheel (MB, CJ2A) uses a 10 tooth bendix.
The 124 and 129 tooth flywheels (CJ3A and later) use the 9 tooth bendix.



Edited by rocketeer - 13 Aug. 2016 at 4:16pm
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montymech View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug. 2016 at 1:03pm
Thank you for confirming  the 124/9 requirement; that probably accounts for the destroyed 97 ring gear?
I suppose when you are far from civilisation or down on cash you chuck in what you have to get mobile. Or, like me in this case, you're just unaware until disaster strikes. I'm well pleased the ringgear was damaged, I wouldn't have given the Bendix tooth count a thought.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote shadow Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 5:17am
This is a common problem and not just with the jeep , I have seen this on many other cars and trucks, the engine will always want to stop on a compression stroke, so with a 4 cylinder engine there will be 2 spots that the engine will tend to stop on, now think that every time you enguage the starter that little gear is spinning and being thrown into the ring gear and over time you are going to have chips and wear on the gears and now and then it may not enguage as good as it should so over time you end up with a ring gear that looks like what you have. I dont knowif this is in the how to section or not but its very easy to replace a ring gear, as long as you have a propane torch and a drill this is a job that may only take 1/2 an hour good luck
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 10:43am
Shadow, what concerned me was the magnitude of the damage to the ring gear. It transpires that the ring gear is a 97 tooth version that is a standard MB fitting .Whoever installed it failed to fit a ten tooth pinion to match; they just reinstalled the CJ3A starter which has a 9 tooth pinion. When I  removed the fly wheel I noticed lots of metal chips, big pieces, littering the block. Inexplicably I did not connect the ring gear damage to the chips; I thought a careless machinist hadn't cleaned up. A couple of hours before the details emerged I had ordered a 97 tooth gear ring form USA unaware that it was not a CJ3A part. Fortunately the difference in time zones meant the order had not been expedited and I was able to  change it; shipping to UK doubles the price of most items.  
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Oilleaker1 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 10:57am
My Ford GPW had the same damage. The previous owner told me he had the starter re-built. It was the correct count, flywheel/starter bendix. I had problems with the starter locking into the flywheel. The only way to release it was shut the Jeep off and rock it in gear back and forth. Try that on a steep hillside after you stall the engine!!! Good post for everyone to read and understand. John
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Post Options Post Options   Thanks (1) Thanks(1)   Quote rocketeer Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 2:02pm
Originally posted by shadow shadow wrote:

This is a common problem and not just with the jeep , I have seen this on many other cars and trucks, the engine will always want to stop on a compression stroke, so with a 4 cylinder engine there will be 2 spots that the engine will tend to stop on, now think that every time you enguage the starter that little gear is spinning and being thrown into the ring gear and over time you are going to have chips and wear on the gears and now and then it may not enguage as good as it should so over time you end up with a ring gear that looks like what you have. I dont knowif this is in the how to section or not but its very easy to replace a ring gear, as long as you have a propane torch and a drill this is a job that may only take 1/2 an hour good luck

A CJ3A starter isn't like all the others. The bendix doesn't spin into the flywheel, it is pushed in with a foot lever which then presses on an electrical switch which in turn spins the starting motor after the bendix is all ready engaged. As long as there isn't a mismatch between the ring gear and bendix it works fine. The problem comes when you try to engage the wider teeth of a 9 tooth bendix into the narrower teeth of a 124/129 tooth ring gear. The bendix doesn't fully engage and has a tendency to spin out because the leading edge of the bendix teeth are pointed. Since the bendix is now spinning it grinds against the ring gear and cause the type of damage seen above.




Edited by rocketeer - 13 Aug. 2016 at 2:06pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 2:41pm
 Reading your post... I see I have more problems:

A CJ3A starter isn't like all the others. The bendix doesn't spin into the flywheel, it is pushed in with a foot lever which then presses on an electrical switch which in turn spins the starting motor after the bendix is all ready engaged. As long as there isn't a mismatch between the ring gear and bendix it works fine. The problem comes when you try to engage the wider teeth of a 9 tooth bendix into the narrower teeth of a 124/129 tooth ring gear. The bendix doesn't fully engage and has a tendency to spin out because the leading edge of the bendix teeth are pointed. Since the bendix is now spinning it grinds against the ring gear and cause the type of damage seen above.

This is the starter that I pulled from my vehicle; it's not a manually pre-engaged starter as described above. The Bendix has the typical helical throw out, there is no shock absorbing spring and nothing to stop the Bendix from inadvertently sliding towards the flywheel when no in use. There appear to be bits missing?  I wonder which vehicle it was fitted to when it was a complete motor.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocketeer Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 3:49pm
OK, first I must apologize for the typo above - 97 tooth flywheel uses 10 tooth bendix. However, the starter you have is not a CJ3A starter and while similar to a CJ2A, the bendix looks a bit different. Are there any identifying marks on the starter?

This is the bendix that Walcks sells, note the difference to what you have. You might want to cancel ordering anything until you figure out exactly what you have.





Edited by rocketeer - 13 Aug. 2016 at 4:16pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 4:50pm
rocketeer, I  think you got it right first time: 97 ring uses 10 pinion. Early CJ3A  has 124 ring with 9 pinion and the starter shaft is supported in the clutch housing. Late  3A, M38,3B CJ5/6 use 129 ring and a self supporting motor shaft with a 9 pinion.

So the motor I have fits the 'pinion and support' description although the vehicle is on 12 volt and the starter may be 6 volt. The motor should be an MZ4137 or M4162. the motor has a variety of numbers:         PS79A ,   5,    0  7809, 3322, J205.
I note in the image you posted that there is a hair spring on the outer end of the shaft which is missing on mine.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote rocketeer Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 7:48pm
The missing spring is important. On that type of starter it starts spinning as soon as you hit the switch. Centrifugal force spins the teeth forward and the spring acts as a cushion until the bendix fully engages the ring gear. Without the spring the teeth are banging into the ring gear.

Sorry I messed up the post earlier. I accidently hit "Post Reply" instead of "Preview" and then got called away, not realizing it went live and when I came back I wasn't sure whether I had corrected it or not before clicking on the wrong button. Sheesh!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug. 2016 at 9:20pm
Hi. It appears that the motor image you posted is of  an  MZ4113.  It was original equipment on the MB and drove a 97 tooth ring. It was fitted with a choice of pinion, 10 teeth for MB and 9  teeth for CJ2A ??? I'm quoting from a Walcks  youtube video. Mr W thinks that there is enough slack in the gears for the 9 tooth pinion to drive the 97 ring??   If that is true then I have gone full circle for my ring gear appeared to have been destroyed by the 9 driving the 97 . There is  the possibility, of course, that the ring gear was damaged prior to the current starter motor being installed because the Bendix teeth don't appear to have any damage. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote shadow Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug. 2016 at 3:21am
I have seen people replace the starter to dance around the problem that the ring gear is worn out, with a new starter or at least a new bendix it hides the problem for a little while. some of the problems that you are seeing can also be caused from a dirty bendix causing slow enguagement into the ring gear, a weak battery or poor conections causing slow enguagement or rotating speed of the starter, all of thies little problems add up very quickley and when the ring gear is worn to the bevel on the teeth of the ring gear it starts to break down very quickly, hope this helps and good luck
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Post Options Post Options   Thanks (1) Thanks(1)   Quote shadow Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug. 2016 at 4:02am
sorry but i should have asked the question , but you say its a cj3a but is the engine a F head or a L head , this helps to identify what you need
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug. 2016 at 5:18am
 Starter drives were designed and built by more than one company, to several different designs and operating characteristics. BENDIX was/is one of those companies. Sort of like Jell-o and Kleenex, I guess. Not all starter drives use the recoil spring seen in the picture of the Walck's product, it all depends on who designed/made the drive unit. I've seen Willys/Auto-Lite starters with and without the spring.
  The starter drive does not "spin" as soon as the switch is activated. Inertia is the tendency for a moving object to continue moving, and for a stationary object to remain stationary. When the starter motor begins to spin, the drive gear wants to remain stationary, the motor shaft turns but the drive gear doesn't, so the spiral teeth in the drive shove it towards the ring gear. It is inertia, not centrifugal force, that causes the drive gear to engage the ring gear, and while the drive gear may be turning some at that point, I wouldn't say it would be "spinning". If it was spinning as fast as the starter motor, it would never engage, it would only make horrible noises, and tear up the drive gear and the ring gear. When the spiral gets dirty or sticky, the drive is slow in moving toward the ring gear, and the motor does get the drive gear spinning closer to the same speed as the motor shaft, and that is when you get that horrible noise.  BW
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug. 2016 at 8:01am
Originally posted by shadow shadow wrote:

sorry but i should have asked the question , but you say its a cj3a but is the engine a F head or a L head , this helps to identify what you need

 Hi. I'm not  familiar with L,F identification, does this help?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote montymech Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug. 2016 at 8:22am
[QUOTE=Bruce W]  Starter drives were designed and built by more than one company, to several different designs and operating characteristics. BENDIX was/is one of those companies. Sort of like Jell-o and Kleenex, I guess. Not all starter drives use the recoil spring seen in the picture of the Walck's  ( etc)

Well thanks for that Bruce.  My starter has in fact got the large spring shown in the Walck's photo. Being more familiar with the Lucas product, I was expecting a large spring on the outer end of the motor shaft. 
   
To be honest I've never given bendix drives that much thought other than to be surprised that one gear being flung at another could survive so long. Your explanation accounts for the systems durability; the pinion is moving axially with very little rotation as it engages. It only attains motor  speed when it hits the stop on the end of the shaft.... as I understand it.
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