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  #1  
Old September 13th, 2015, 17:47
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xeroOTG xeroOTG is offline
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NP242 rebuild with upgrades

I am in the process of rebuilding a NP242. One think led to another, and I went from a hack and tap to buying a Tom Woods insane 32 spline super duper main shaft, so I figured, "what the heck, lets see if I can also do the 1.25" chain too!". I picked up a cheap NP242D out of a dorango today to see WHAT the differences were, since most of the internet was devoid of much tech about the 242HD. I am thinking that the differences are too much to make a NP242 LD with a 242HD chain.

First I found that the rear half of the case was taller on the HD, and that the oil pump rides the main shaft via a snap ring and a bronze bushing instead of bottoming on the case and uses a lipped seal. The diameter of the shaft at the oil pump on the 242HD must be .25" smaller, so I can't use the HD pump on the LD shaft.

Next I removed all of the snap rings to remove the chain and found the bigger (1.25" from the HD) sprocket on the main shaft had an additional .25" of collar on the differential output.

When I found this, my plan was to use the Tom Woods shaft with the HD differential and 1.25" sprockets, along with the rear case from the HD. This was fine and dandy, but the collar that the differential's retaining snap ring was supposed to go into was .25" behind the differential... so I was now thinking I would get a friend with a lathe to machine the output of the differential to ride .25 over the collar on the main shaft, which was great till the oil pump came back into the equation. Not an option. the sprocket dragged on the oil pump, so thats not an option... so has anyone build a 1.25" chained NP242 with a Tom Woods main shaft? Is the .25 of extra chain worth what it would take to get it all to fit?

Here's some pictures to demonstrate my conundrum.



The gears are substantially different by width, diameter and tooth count, but has the same splines.



Differences in the differential.



Honestly, the 242HD shaft doesn't look as strong as the 242 Tom Woods shaft, it necks down at the output. Because of this, you could only re spline it for a smaller 27 splines.



It looks like the .25" is gained by lengthening the bearing race, and moving the rest of the gear train .25" towards the rear of the case.



This doesn't even go into how much difference there is in the differences in the tail housing.

ehall, I am sure you will see this, I saw on your build thread that you were going to build a 242HD, what was your plan?

The stuff I have got to work, was a 32 spline front output and a 6 pinion low range (I already had one).
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Old September 13th, 2015, 18:16
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Re: NP242 rebuild with upgrades

Here's another comparison:

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Old September 14th, 2015, 05:53
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Re: NP242 rebuild with upgrades

The only failures of a 242 that I have heard of is the shaft. I have never personally seen or heard of a chain failing. I have the woody shaft and am not concerned, but I don't go all hardcore and I am only on JK Rubicon wheels and tires.
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Still need to: truss, shave, relocate shock mounts on the 8.25; Regear with selectable lockers; 2x6 rockers, belly skids, rewire "stereo" ...
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Old September 14th, 2015, 06:46
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Re: NP242 rebuild with upgrades

see here http://www.naxja.org/forum/showthrea...#post244190381

My expectation was to use the HD case and chain/sprockets, a 6-pinion planetary low-range in the front, and the TW mainshaft. I don't have any of the parts together yet

In your pictures, the differential does not look any different except for the taller collar, and the TW shaft looks like a regular SYE shaft (assuming with larger output). I would think you could put the regular pump on the regular differential on the TW shaft and be good to go
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Old September 14th, 2015, 07:20
tonytech tonytech is offline
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Re: NP242 rebuild with upgrades

Where did you purchase the parts?
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Old September 14th, 2015, 07:42
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Re: NP242 rebuild with upgrades

Quote:
Originally Posted by iluv83vettes View Post
The only failures of a 242 that I have heard of is the shaft. I have never personally seen or heard of a chain failing. I have the woody shaft and am not concerned, but I don't go all hardcore and I am only on JK Rubicon wheels and tires.
I found some data sheets that put the 1.25" chain at weaker than the 1" chain because the pitch is 3/8" on the 1.25". The only advantage then is the .2" larger OD of the 1.25" sprockets.

Quote:
Originally Posted by ehall View Post
see here http://www.naxja.org/forum/showthrea...#post244190381

My expectation was to use the HD case and chain/sprockets, a 6-pinion planetary low-range in the front, and the TW mainshaft. I don't have any of the parts together yet

In your pictures, the differential does not look any different except for the taller collar, and the TW shaft looks like a regular SYE shaft (assuming with larger output). I would think you could put the regular pump on the regular differential on the TW shaft and be good to go
So.... Yes. That was one of my schemes. If you use the HD differential (with its longer collar) you can't put on the snap ring that holds it on the main shaft. The HD shaft's bearing race is physically .25" longer to accommodate this.


Quote:
Originally Posted by tonytech View Post
Where did you purchase the parts?
I got both cases from the scrap yard and the main shaft from Tom Woods
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Old September 14th, 2015, 07:53
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Re: NP242 rebuild with upgrades

Quote:
Originally Posted by xeroOTG View Post
If you use the HD differential (with its longer collar) you can't put on the snap ring that holds it on the main shaft. The HD shaft's bearing race is physically .25" longer to accommodate this.
but can you use the regular differential?
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Old September 14th, 2015, 09:52
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Re: NP242 rebuild with upgrades

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but can you use the regular differential?
That's a great question, I will confirm when I get home. I don't think so. The length of the differential on the shaft is based off of the inside bore of the differential sprockets. My only option would be to bore out the differential output sprocket which would cause oil pump interference or require me to make spacers to move the oil pump galley further up the shaft. This would also mess with the amount of thread engagement the output flange nut would have (placing more load on the new output bearing I suppose?) and shift the speedo worm out of the center of the speedo drive's position. That could be modified by cutting new grooves for the snap rings for the speedo drive worm... but at what cost?

If I moved the sprockets towards the input I would have to modify the shift sprockets, as the .25" lost would interfere with the 4FT/4PT selector.

I think that roller rockers instead of roller pins make the chain stronger, based off of this page. The European 242(ECE) came with rockers, I think I will start pounding down that path.

Some math:
Roller Pin
____
Width | Ultimate Tensile LBS - 3/8" Pitch | 1/2" Pitch
1" | 3750 | 7500 < Current Standard Chain
1.25 | 4690 | 9300

Rocker Joint
____
Width | Ultimate Tensile LBS - 3/8" Pitch | 1/2" Pitch
1" | 7500 | 10,000 <- Euro Case
1.25" | 9375 <- 242HD/242D | 12,500

So basically the rocker jointed chain in 1" with 1/2" pitch out of a 242ECE will be stronger than the 242HD 1.25" x 3/8". (HV-061)

Here's the document I used to find info about the pitches/widths of chains.

Does anyone agree or am I in a camp of my own?
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Old September 14th, 2015, 12:54
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Re: NP242 rebuild with upgrades

If the regular differential doesn't fit on the TW shaft, you could also try removing the needle bearings. They aren't entirely necessary
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Old September 14th, 2015, 20:12
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Re: NP242 rebuild with upgrades

Quote:
Originally Posted by ehall View Post
If the regular differential doesn't fit on the TW shaft, you could also try removing the needle bearings. They aren't entirely necessary
I'm not quite sure what you mean by this, the differential needle bearings keep everything centered, especially when the chain is under load.

So I tried the tall (1.25") differential output sprocket. No workey.


The top of the differential output rests on the collar on the main shaft.

This prevents the snap ring on the input side of the shaft from going on:


Here is a better illustration of the differences in the differential bearing race section of the main shaft.

The smaller collars on the two shafts that butt up against the tallest collar are spacers for retaining the needle bearing.

I talked to an engineer at work, after digging through the documentation morse has for the HV and standard inverted tooth chain they make, we decided that even with mechanical advantage of the .2" larger sprockets, when combined with the 3/8" pitch x 1.25"W rocker joint chain it would be weaker than the 1/2" pitch x 1"W rocker joint chain that is in the 242ECE.

There is no difference between a 242HD, 242WJ or a 242D according to the documentation I have found over the past couple weeks of research.

Its almost like the 242WJ/HD/D is a downgraded H1 case, which would have had the 1/2" pitch chain that is so much stronger with the 1/4" longer main shaft and case rear. The WJ case does not have the 6 pinion low range, doesn't have that much stronger of a chain than the standard 242, and even features a potentially weaker lubrication system since the tolerances at the pump are looser. At least it has a 32 spline front output. It is stronger than a standard case but if you can I would do the 242AMG. That way you at least get a cooler, with your wide chain and secondary bearing races in the differential. This differential only has the taller output sprocket and an additional bronze bushing in the top half. I'm underwhelmed, thank god I'm not out much $$$.

All that being said the 1/2" pitch x 1"W rocker joint chain is out of production according to Morse/Borg Warner (I called them) so I might not be able to repair this box in the future. I got one from Novak, they had a couple on hand. I'm not positive the drive/driven sprockets are the same even though the parts manual has the 242 and the 242ECE with the same part number. Ill update this once I have the HV-061 in hand.
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Old September 15th, 2015, 11:51
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Re: NP242 rebuild with upgrades

It is seeming that a great "built" 242 would be the standard case, with the TW shaft, the 6 pinion reduction, and the Euro chain (assuming the sprockets work with that chain).

This would be great if it came together. I've been seriously considering a 242 swap into my diesel SJ and this would be a great updated unit.
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Old September 15th, 2015, 12:13
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Re: NP242 rebuild with upgrades

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Originally Posted by DieselSJ View Post
It is seeming that a great "built" 242 would be the standard case, with the TW shaft, the 6 pinion reduction, and the Euro chain (assuming the sprockets work with that chain).

This would be great if it came together. I've been seriously considering a 242 swap into my diesel SJ and this would be a great updated unit.
That is exactly my plan! I have already started with degreasing the standard case, replaced all bearings and seals, assembled the 6 pinion low range and input assembly, main shaft, differential, and front output sprocket.


Spray lithium makes installing the needle bearings a cake walk, just hit it hard, stack a couple, then coat them, repeat till done. It took less than 10 minutes to do the whole shaft.

While trying to pull the front output bearing in the rear case half I messed up the bearing seat, so I ordered a new rear half. It came in yesterday.



The differential,I used the differential case from the NP242D since it had less wear than the NP242 differential I had, but used the short input so it would all snap together.


I will get all of the bushings in the shift rail replaced and installed tonight. I am mocking it up with the old 1" sprockets, but I ordered new ones since these show wear.

I got a narrow bearing 242 rebuild kit off Amazon, a transparts warehouse branded one, and so far I am very impressed with the quality of the seals. All of the stock seals were single lip, these are double lipped. I also picked up Automatic Transmission RTV for its temperature and ATF resistant properties. We will see if I am shooting myself in the foot for using something unproven...


I love the sheen of a clean aluminum case, but I couldn't get all the corrosion off of this one.

As a side note I am putting this behind an AX15. I'm sure there will be some hissing and booing, but I love the 242 in my wife's jeep with the aw4 and want one for mine.
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Old September 15th, 2015, 12:45
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Re: NP242 rebuild with upgrades

Kind of curious. I checked the 242-AMG used in the HMMV and it is a single-pin chain. Look at http://www.ebay.com/itm/like/231204382226 and others, they all show an AMG box. Maybe the steel is better grade or something. The link you gave earlier also says the pitch is different, not sure what that means. If the double pin is stronger then the 242-ECE chain is stronger than the HMMV chain

Something else for your rebuild: make sure to dissassemble and thoroughly clean the old differential. There is a synchro in the middle of it, and the wear dust from the brass gets into all the little corners and blocks up the flow. Also, I put a bottle of Lubegard 60902 in after my last rebuild and it seems to have helped. That stuff is concentrated ester and paraffin, really improves the slipperiness internally.
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Last edited by ehall; September 15th, 2015 at 12:49.
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Old September 16th, 2015, 10:50
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Re: NP242 rebuild with upgrades

Now we just need someone to machine a ARB or ECTED to replace the open diff...
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Old September 16th, 2015, 11:15
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Re: NP242 rebuild with upgrades

Already exists ... its called Part-Time
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