Swapping parts: engine/tranny/transfer case or? - JeepForum.com
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post #1 of 13 Old 09-17-2017, 05:16 PM Thread Starter
FiveLakesYJ
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Swapping parts: engine/tranny/transfer case or?

It's been a long time since I've posted here. I have a build thread to finish, or at least update as I'm still building... Unfortunately, my health took a downturn and I'm finally feeling up to doing this again.

Anyway, I have a 1995 YJ that I've done a lot to. It has a 2.5l engine and AX5 tranny. I stumbled (almost literally) onto a 1994 YJ with a 4.0l engine/AX15 that is being sold for parts. It runs great, shifts to all gears and the transfer case is solid. It also has a number of other parts that I would love to have as spares.

The conundrum I find myself in... The AX5 is almost ready to die. The AX15 would be my choice to replace it with. No problem there. I've already decided to replace both the tranny and transfer case at the same time rather than modify the current transfer case. I'll also be putting in an SYE while I have the parts out. Still not much of a problem. Now we take a turn... The engine... I would love to have the 4.0 in my Jeep. My 2.5 is nowhere near needing work so I'd like to leave it in. On the other hand, I have a complete, running 1994 YJ as a donor vehicle to my 1995.

If I keep the 2.5, I'll need to find a Dakota bellhousing. If I swap the engine, I'll need to relocate the motor mounts and probably some other stuff that I had to move when I put on the MetalCloaks. The engine swap seems to make sense since I have pretty much everything I would need, I think. The 2.5 has 150,000+ miles, the 4.0 is just under 135,000. If the 2.5 ever dies, I would most likely want to put in a 4.0. If I keep the 2.5, I'd be happy. But, if I do that and later change my mind and want the 4.0 more, I'd be throwing away a lot of work.

Here's what it all boils down to... I have a 1994 YJ that will never again be roadworthy. It has everything I need to do the swap. Is it worth the time and trouble to swap everything and am I missing anything? It seems pretty straight forward, but I'm wondering what is hiding to make this more difficult than I imagine.

If it was you in this position, what would you do? What does it look like I'm missing?

Many thanx

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post #2 of 13 Old 09-17-2017, 06:04 PM
Jeepsr4me
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Yes its worth the trouble to swap.. Welding motor mounts is NOTHING on the scale of things to do.
If you dont have welder, find a friend or rent one or bring to a welder to do.. ITS VERY SIMPLE..

since you have all the parts to do swap this is going to be just a gut and replace deal for ya..

DO it and never look back. As a plus you can sell off the 2.5 stuff and now you will have axles that are way better geared for a 4.0 and 32s..
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post #3 of 13 Old 09-18-2017, 07:35 PM Thread Starter
FiveLakesYJ
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Thanks Jeepsr4me. I needed the boost in confidence for making that decision. I'll have the pro that welded my frame weld in the motor mounts. I think I have the mechanical side of this figured out. The wiring is what will be my hesitating point. I've found a lot of articles for swapping a 4.0 in, but they are all using a Cherokee engine and most often newer. Since I have the entire Jeep would the simplest way be to use the 4.0's harness? I've done low voltage wiring for years but never on a Jeep. Using the 2.5 harness seems to be more work than necessary. What would be involved in installing the 4.0's ECM?
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post #4 of 13 Old 09-18-2017, 07:40 PM
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Quote:
Originally Posted by FiveLakesYJ View Post
Thanks Jeepsr4me. I needed the boost in confidence for making that decision. I'll have the pro that welded my frame weld in the motor mounts. I think I have the mechanical side of this figured out. The wiring is what will be my hesitating point. I've found a lot of articles for swapping a 4.0 in, but they are all using a Cherokee engine and most often newer. Since I have the entire Jeep would the simplest way be to use the 4.0's harness? I've done low voltage wiring for years but never on a Jeep. Using the 2.5 harness seems to be more work than necessary. What would be involved in installing the 4.0's ECM?
The nice thing is you can pull the 4.0 /Ax15/ t case as one and swap it in as one....

Use the 2.5 harness and 4.0 computer and add the 2 extra wires for the injectors... Do a search on that.. its easy....
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post #5 of 13 Old 09-18-2017, 07:53 PM
Jeepsr4me
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Just use the whole harness from the 4.0.... since you have it complete.. wiring is just pull and replace with a complete donor..
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post #6 of 13 Old 09-22-2017, 08:05 PM Thread Starter
FiveLakesYJ
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I finally got my donor YJ home. After closer inspection, the frame is a lot worse than I expected. Not a problem since I won't be using it. Taking a chance on a gravel road, I took it for a drive. It shifts through all gears smoothly, the transfer case shifts and works great. The first thing I noticed was that it started much easier and faster than my 2.5. It idles smoothly and runs smooth through accelerating. I changed the oil and the oil is unpolluted. No metal shavings or signs of leaks. No signs of burning oil. My son is coming over tomorrow and we'll do a compression test, more out of curiosity than anything. Over all, the engine seems sound at this point. The transmission shifts smooth and never wants to pop out of gear. It takes a firm hand to shift the transfer case and always went to whatever position I put it in. I'm feeling much better about this than I was before.

My plan right now is to run 'Little Boy Blue' (the donor) a couple more times being very careful of not stressing the frame too much. I'll take the engine, tranny and transfer case out as one unit. I'll put in the Advance Adapters SYE and remount the transfer case. I'll cut the frame parts of the engine mounts off Little Boy Blue and clean them up. Here's where I hope to get some advice... I want to slide the engine combination into my Jeep and set the transmission mount into the skid plate and use that as a guide to mount the motor mounts on the frame. I just realized I'll need to take the transfer case drop out before I slide the new engine in. To me, this seems the best way, but if there is a better way, I'd love to hear it.

I'll be using the 4.0's engine harness. I've already had people ask about buying parts I won't be using. I'm going to have to think seriously about what parts I want to keep as spares. If I play my cards right I could come close to breaking even on this whole thing (minus the SYE and new drive shaft).

Another question... Will my current front drive shaft work or will I need to use Little Boy Blue's front drive shaft? Any other parts I would need to swap or keep as spares?

Many thanx for any help.
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post #7 of 13 Old 09-23-2017, 06:07 AM
JeeperDon
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Unless the tubs are off, I think it would be a lot easier to pull the t-case first and just leave the engine and trans together. The t-case is just an easy 6 nuts.
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post #8 of 13 Old 09-23-2017, 07:48 PM Thread Starter
FiveLakesYJ
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JeepeerDon, I like your idea and will do it that way. Many thanx.

On the down side, my son and I did the compression test today and it was not good. Considering the results and assuming the rented compression tester was accurate, I'm going to need to rebuild the engine before I put it in. I'm at a loss to understand why the engine runs smooth and has a lot of power, no missing or hesitation, and yet the results are so bad:

Cylinder Dry Wet
1 80 100
2 95 115
3 100 115
4 80 95
5 90 95
6 95 110
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post #9 of 13 Old 09-23-2017, 07:56 PM
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Are you doing the test correctly? Open The TB and zip tie it open. Take ALL the spark plugs out. Hook battery charger to the battery.. One at time test each one, letting the engine turn about 5 times total. I count the compression strokes as they pulse the tester in your hand..

Then do a wet test... Dont have to be a lot of fluid either.. This is a test to see if the rings are seating.
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post #10 of 13 Old 09-23-2017, 08:21 PM Thread Starter
FiveLakesYJ
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Jeepsr4me, here's what we did...

Started the engine to get up to operating temp. Removed all spark plugs and disconnected the injectors. Blocked the TB open with a screwdriver. Hooked up the charger after testing #3 during the dry test. We counted 5 compression strokes on each cylinder. We let the charger sit for about 10 minutes and then did the wet test. We used an oil can and squirted one time in cylinder one, let it sit for a couple minutes, tested the compression. On to cylinder two and repeated. We didn't put oil in all the cylinders at once, just as we tested each cylinder.
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post #11 of 13 Old 09-23-2017, 08:37 PM
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Those numbers are low... I have seen engines that were never run hard, glaze the cyl walls. And the rings just can not seal.

Couple ways to fix this. One you pull the head you can tell pretty quick if the walls are all slick and glazed over. If so just ball hone and new rings and you good to go. New set of bearings for good measure. Had lots of luck doing just this. Afterward 145-155 range drry.
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post #12 of 13 Old 09-23-2017, 08:56 PM Thread Starter
FiveLakesYJ
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That sounds good. Thank you. We'll pull the head tomorrow and see what it looks like. Just an extra thought here... Since I'll have the head off, should I rebuild that before reassembly? It has close to 135,000 miles.
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post #13 of 13 Old 09-23-2017, 09:28 PM
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Could have it checked and decked,, Not sure on how easy it is to find a good machin shop near ya. I have a good one and they charge like 40 bucks to deck and pressure test... Sometimes I can talk them into swapping in new valve seals for me for that too...
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