242 into a 231 swap questions

I was hoping to swap my 242 from my 87 xj into my dd which is a 93 xj. I've done a lot of research so I dont need any thread links unless they answer this specific question. I have a post 91 231 as a spare so I could swap the input gear into the 242 in shop and have no down time for the dd. However I just learned that there is a problem with the speedo gear not being compatible in the swap? Does anyone know any specifics on this? I realize the 87 is cable driven and the 93 is electrical. Is this a problem or is it just a straight speedo housing swap? Anyone who has done this? I would appreciate the info. Thanks all.

Looks like I answered my own question, post 5:http://www.naxja.org/forum/showthread.php?t=65090&highlight=242*

tkjeeper said:

I was hoping to swap my 242 from my 87 xj into my dd which is a 93 xj. I've done a lot of research so I dont need any thread links unless they answer this specific question. I have a post 91 231 as a spare so I could swap the input gear into the 242 in shop and have no down time for the dd. However I just learned that there is a problem with the speedo gear not being compatible in the swap? Does anyone know any specifics on this? I realize the 87 is cable driven and the 93 is electrical. Is this a problem or is it just a straight speedo housing swap? Anyone who has done this? I would appreciate the info. Thanks all.

Click to expand...

Of a bigger concern would be the input gear pitch,it changed right about those years.

what do you mean by pitch rcp? in my research on here and on the 242 and 231 in shop the input gear was identical, that was in my 2 I have in shop anyway as well as this thread:
http://www.hobbyguild.com/jeep/index.html, tell me what you think

tkjeeper said:

what do you mean by pitch rcp? in my research on here and on the 242 and 231 in shop the input gear was identical, that was in my 2 I have in shop anyway as well as this thread:
http://www.hobbyguild.com/jeep/index.html, tell me what you think

Click to expand...

The input gearset is cut as "helical" gears, not "spur" gears. With spur gears, "pitch" refers to the distance between teeth (there is a formula for figuring the number of teeth relative to the pitch and outside diameter, and the three values are related.)

With helical gears (they resembles loose spirals, if you were to continue them all the way around,) you have to add "helix angle" into the calculations for cutting them - this is the angle of the helix WRT the axis of the gear. Meching helical gears with even slightly different helix angles is a Very Bad Thing(tm) - especially when the loads of a drivetrain are involved. The first time you drain your transfer case to change the fluid, you'll drain your gear teeth as well if they're mismatched. Ouch.

Since you're so close to the break point (and I can never quite recall when that really was...) you may be better off ordering a new input gear from somewhere like Novak, or seeing if one can be had from Magna/New Process Gear (I don't know about the latter. I'm sure Novak does NP231 inputs, but I don't know if they do NP242s as well. It would stand to reason that they do.)

But, a helix angle mismatch of even a few minutes of angle, with the torque load those gears are going to see, is going to be enough to wreck them in short order!

Jon, you're raining on my parade! lol. Thanks sir