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Unread 07-28-2013, 02:33 PM   #1
fishadventure
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older 258 into 91 YJ - questions

Hi. I am new to this forum but I have been on various boards since the mid 90s. So I know people hate when a new 'member' joins up and asks a question that is common and found in the archives. So I just spent an hour searching and reading but apparently I am not using the "correct" search terms to find my answer. I read over the FAQ too http://www.jeepforum.com/forum/f12/4...mation-537763/ Anyway, it is time to ask the question.

Will an older but running carbureted 258/4.2 bolt up to a (I believe) AX4 in a 91 YJ that came with a 2.5l 4 banger?

I know the 4.2 it is low on horsepower but has decent torque. And it is $100 and complete- has a Ford electronic ignition with vacuum advance. I like the dependable reputation and it is inexpensive to maintain.

I can deal with the motor mounts (I probably will get them with the motor anyway but if not can fabricate whatever is needed) but I don't know these things and couldn't find them with my search:
  1. Will the 4.2 bolt pattern match the bolt pattern from the 2.5 bellhousing?
  2. Will the 4cyl/AX5 clutch disc work with the 258 pressure plate? (because the splines are different)
  3. OR do I just / can I just use the 2.5 clutch and pressure plate on the 258 flywheel?
  4. Other than radiator hoses, fuel pump issue, and sender/gauge wiring; is there anything else that I, the-skilled-and-tool-possessing-but-otherwise-idiot-jeep-newbie, is missing here?

Last question: I can't seem to find the nice 4.0 I6 local to me for under $1200 and then I still need to buy an engine management computer, deal with sensors, and figure out the wiring, right? So I would prefer the 180HP engine but that isn't doable in the budget- the 258 is affordable to me. With the ECM and motor it looks like close to $1500 and then it seems I need to deal with the tranny, too. I see rebuilts for $1800-ish. I get the sense that $1200 is way too high for a complete 4.0? What should I expect to pay?

In the end I think that old 258AMC is the least bucks to get the '91 back on the road again. Rebuilding the 4-banger correctly was just adding up to enough cash that it stopped making sense. I miss the old days when you'd buy a JC Whitney kit to rebuild a 6cyl Chevy complete with pistons and it only cost about $120 with shipping. Wait; am I getting old?

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Unread 07-28-2013, 05:46 PM   #2
Berniebikes
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others may have to join in, but the AX-5 tranny and bell housing for the 4 cylinder I do not think is compatible with the 258 I6. You need to find an AX15 transmission and bell housing for the I6 and give up on using the AX 5.

As for torque and power, have you considered putting a 4.0 head onto your 4.2? You can gain most of the difference in horsepower, especially if you go all the way and convert to MPFI while you are at it.

Another alternative is to grab the 4.2, put an AX15 behind it (usually available for less than 500 with bell housing) and do a junkyard TBI for performance and maintainability. Total package could probably be done for less than a grand.
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Unread 07-28-2013, 06:35 PM   #3
fishadventure
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258 into a 91YJ

Quote:
Originally Posted by Berniebikes View Post
others may have to join in, but the AX-5 tranny and bell housing for the 4 cylinder I do not think is compatible with the 258 I6. You need to find an AX15 transmission and bell housing for the I6 and give up on using the AX 5...
Reading between the lines a little: Will the AX15 will bolt to the stock transfer case? Or were you thinking of the tranny and transfer as an assembly? I have access to an AX15... but it doesn't come with a transfer case and the guy selling says he doesn't know its condition.

I would rather not have to buy the AX15 if it is a matter of a few new holes or making an adapter out of plate. Especially if I have to buy a transfer case. too. I have adapted mongrel combos in Chevies from scratch. So the skillset is there. I do not have Manufactured Product Dependency Syndrome.

The thing is I just don't know jeeps very well so I am leaning on the knowledge base here...

As far as the other suggestions- I appreciate them. What it comes down to at the moment is if it takes $1000 I can't do it this year. I /can/ buy the 258 if it can be made to work for under $300 total. On the other hand, if I need to spend $1K, I would just go for the 180HP 4.0 complete with computer. That would perfectly suit my purposes.
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Unread 07-28-2013, 07:25 PM   #4
lah2420
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Even if you could mate the AX5 to the 258, it is pretty light duty for the 6 cylinder. I agree with finding an AX15, but you would either need a different tcase or would need to change the input gear to the tcase. I know for certain the disc and pressure plate on the AX5 is much smaller than what comes on the 258. I seriously doubt they would even bolt up.
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Unread 07-28-2013, 09:08 PM   #5
schaef89
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In addition to the trans issue you'll have to cut the engine mount perches off the frame and reweld them in the 6 cyl locations. The YJ frames are not universal between engines
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Unread 07-29-2013, 04:31 AM   #6
fishadventure
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Quote:
Originally Posted by lah2420 View Post
light duty for the 6
The specs on the old 258 are 115HP and the 4cyl 2.5 is 125HP so I don't think have a concern here

Quote:
Originally Posted by schaef89 View Post
In addition to the trans issue you'll have to cut the engine mount perches off the frame and reweld them in the 6 cyl locations. The YJ frames are not universal between engines
I have the motor mounts covered. The 258 was in a CJ previously. Removing the YJ mounts and rewelding isn't a big deal for me.

I actually know of several YJs with 4cyl that lunched an AX5, so I know it makes sense even with the low HP of the 258.

My goal here is to get the thing on the road this month. The dollars to do this are pretty tight. Next summer spending more is doable- but not this summer. I have been sitting on this project for a few years and this thing needs to stop being stored and be registered!

So basically what I am hearing here is that the AX15 will bolt up to the 258, but unless I mod the t-case with a different shaft I need a transfer case as well. That is probably the most dollar and time efficient.
Then those items are bolt-in compatible with the existing YJ stuff, correct?
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Unread 07-29-2013, 04:39 AM   #7
schaef89
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I'd say swapping your trans will be the best bet and save you headache.

The horsepower of the 258 isn't the problem, it's the torque. It has twice the torque of a 4cyl and that's what makes the ax5 a bad idea. Most people with 4cyl jeeps (me included) have had problems with the ax5 in the stock application. That's why alot of people don't have faith in it
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Unread 07-30-2013, 10:59 AM   #8
fishadventure
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Thank you for all the information. This has been so useful to round out my not-so-broad Jeep knowledge.

So the best I can come up with locally is a Peugeot transmission and transfer case which the owner claims will fit behind the 258 and bolt into the YJ. It is my understanding this tranny came behind the 4.2 and the 4.0, but it is not as good as the AX15. Can't find an AX15 that I trust to buy... But the price is right on the BA 10/5 and comes from a reputable guy so I am fine with it for my purposes- I don't have any big off-road plans for now anyway- just driving to work and towing my boat occasionally.

I can spend the winter locating a good AX15 and the right input shaft for the txfer case. Or I may wait until next summer when I have the cash and buy a 4.0 out of something.

The questions I have unanswered at the moment are these:
  • Can anyone confirm that the BA10/5 is a swap-in that won't need driveshaft/yoke changes and part chasing?
  • What should I expect to pay for a good AX15 alone?
  • What should I expect to pay for a good AX15 and transfer case complete?

I called a couple of junk yards on the AX15 and I was given a price of almost $1500 for the tranny and $750 for the xfer so it looks like private sale is going to be necessary. Unless I am really that all wet those prices are ridiculous- I can buy a running junker jeep with the right pieces for less than that although that isn't even in the budget. But that's Vermont for ya- if you're selling something you get told it isn't worth anything but if you need something- well the hawkers want your firstborn and dibs on the second!

I think I am settled on the old 258- just getting the stuff I can't make myself (tranny/transfer) needs to be confirmed. Learning a lot here - again, thanks for the responses.
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Unread 07-30-2013, 11:27 AM   #9
schaef89
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Quote:
Originally Posted by fishadventure View Post

The questions I have unanswered at the moment are these:
  • Can anyone confirm that the BA10/5 is a swap-in that won't need driveshaft/yoke changes and part chasing?
  • What should I expect to pay for a good AX15 alone?
  • What should I expect to pay for a good AX15 and transfer case complete?
The BA 10/5 came in YJ's up to 1989, some 89's were lucky enough to get the AX-15 (late year production). It was never behind a 4.0, but you will need new driveshafts regardless. The bigger trans for the 6 cyl's are longer which push the transfercase rearward

Someone can jump in and correct me if i'm wrong but I think the BA10/5 can bolt straight up to your NP231 tcase because it uses a 21 spline output instead of a 23 like the AX-15

I think those prices are crazy to be honest. I see AX-15's around here go for 400 bucks, not commonly trans/tcase pairs
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93 YJ, 4.0L HO/32RH/NP231 - Sold
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Unread 07-30-2013, 11:43 AM   #10
jbrown73
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Quote:
Originally Posted by schaef89 View Post
Someone can jump in and correct me if i'm wrong but I think the BA10/5 can bolt straight up to your NP231 tcase because it uses a 21 spline output instead of a 23 like the AX-15
^This

I am looking to change out my BA10/5 for an AX-15 and will have to acquire a different bell housing and change out the output spline of the t-case to the 23.......and those prices you were quoted are friggin ridiculous!
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Unread 07-30-2013, 11:49 AM   #11
roadyrob
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the ba 10 will bolt to the 258, you can reuse your 4 cyl transfercase as the spline is the same on the ba10. not 100% sure on the drive shafts but I believe they are the same.
if the 258 is 87 or older it will have the ford type starter, your jeep has the newer style so the wiring is different. you should be able to change the flywheel to an 88-89 and run a newer starter. depending on the year of the 258 you may need the ecm and wiring harness or change the distibutor to something like a HEI.
engine swaps are never simple.
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Unread 07-30-2013, 12:01 PM   #12
zeus87gn
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Quote:
Originally Posted by fishadventure View Post
So the best I can come up with locally is a Peugeot transmission and transfer case which the owner claims will fit behind the 258 and bolt into the YJ. It is my understanding this tranny came behind the 4.2 and the 4.0, but it is not as good as the AX15. Can't find an AX15 that I trust to buy... But the price is right on the BA 10/5 and comes from a reputable guy so I am fine with it for my purposes- I don't have any big off-road plans for now anyway- just driving to work and towing my boat occasionally.
Fish,
Yes, that BA/TC combo will bolt to the 4.2, BUT....watch out that Puko trani may have a NP207 TC attached to it - That setup did the job in a stock Jeep but won't handle any type of towing or larger than stock tires for long...from my experience anyway...and will need to be replaced in the future - I guarantee it - my 87 went thru 3 BA's before I got smart and swapped to the AX15

Also, the 231 TC you have is stronger than the 207 and easier to get parts for should you ever need them - I seem to remember that the input shaft of the 207 isn't compatible with the AX15 and there are no replacement shafts available


Quote:
Originally Posted by fishadventure View Post
I can spend the winter locating a good AX15 and the right input shaft for the txfer case. Or I may wait until next summer when I have the cash and buy a 4.0 out of something.

The questions I have unanswered at the moment are these:
  • Can anyone confirm that the BA10/5 is a swap-in that won't need driveshaft/yoke changes and part chasing?
  • What should I expect to pay for a good AX15 alone?
  • What should I expect to pay for a good AX15 and transfer case complete?

I called a couple of junk yards on the AX15 and I was given a price of almost $1500 for the tranny and $750 for the xfer so it looks like private sale is going to be necessary. Unless I am really that all wet those prices are ridiculous- I can buy a running junker jeep with the right pieces for less than that although that isn't even in the budget. But that's Vermont for ya- if you're selling something you get told it isn't worth anything but if you need something- well the hawkers want your firstborn and dibs on the second!

I think I am settled on the old 258- just getting the stuff I can't make myself (tranny/transfer) needs to be confirmed. Learning a lot here - again, thanks for the responses.
The 258 is a great motor, but don't waste your time on a BA trani - they aren't worth it
I agree with everyone else on the prices you were quoted - way too high
Keep looking for the parts you need - the right deal will come along

My AX15 I got for $400 and it needed another $400 of repairs
I got my 231 for $75 but it needed to be put back together with new seals and a chain
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Unread 07-30-2013, 12:25 PM   #13
fishadventure
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Quote:
Originally Posted by roadyrob View Post
the ba 10 will bolt to the 258, you can reuse your 4 cyl transfercase as the spline is the same on the ba10. not 100% sure on the drive shafts but I believe they are the same.
Good info. Thanks. Not keen on the BA but other than my time for $150 for xfer and tranny I consider it disposable.

Quote:
Originally Posted by roadyrob View Post
...if the 258 is 87 or older it will have the ford type starter, your jeep has the newer style so the wiring is different. you should be able to change the flywheel to an 88-89 and run a newer starter. depending on the year of the 258 you may need the ecm and wiring harness or change the distibutor to something like a HEI. engine swaps are never simple.
This motor was in a '87 CJ for a while and has a Ford HEI so no ECM or wiring woes. I think I can figure it out pretty easy. But that is all good info and I appreciate your time even if it was just typing for a few secs.

I should get a call tomorrow- I think I found an AX15 and xfer still in a wrecked jeep for $500 but I might not need it

Thanks to all.
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Unread 07-30-2013, 05:38 PM   #14
lah2420
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Quote:
Originally Posted by schaef89 View Post

Someone can jump in and correct me if i'm wrong but I think the BA10/5 can bolt straight up to your NP231 tcase because it uses a 21 spline output instead of a 23 like the AX-15
Here's a list of transfer inputs with tranny and year:

FLUSH 23 1987-2002 (999/904)
LONG 23 1989-2002 (AX15)
FLUSH 21 1987-2002 (AX4/AX5 UP TO 1996) SOME AW4
LONG 21 1987-89 PEUGEOT (AX5 1997 & NEWER)
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Unread 07-30-2013, 05:50 PM   #15
clarythedrill
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hey fish,

i am in vermont also, and have been looking at swapping out my 2.5 also. look on vermont craigslist, under auto parts (or whatever it says) and type in jeep engine. one of the things that pops up is a jeep 4.0 with AX15 and x-fer case for sale. the pictures will be of an ugly red YJ. his prices are very reasonable. i think he wants 350 for the engine and transmission, and 150 for the x-fer case. hope this helps, and good luck.

EDIT: he is located at grande isle, about an hour from you. good luck
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2.5 , 258 , clutch , motor mount , swap

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