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1995 YJ Wrangler: Out with the 2.5L Four and AX-5

Jeep YJ Jeep inline six Jeep 4.2L AX15 Jeep how-to

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#1 Smokie

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Posted 03 August 2013 - 06:37 PM

I have a 95 Wrangler with the 2.5L AX-5 combination. I have the opportunity to replace this combo with the 4.2L AX-15. Other then the engine and transmission swap are there any hidden changes that will have to be made for this swap to work?



#2 Moses Ludel

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Posted 03 August 2013 - 08:19 PM

Hi, Smokie, welcome to the forums and thanks for posting this topic!  I've talked around this subject in other topics related to the AX5 and AX15 differences and even specific discussion about the 2.5L versus 4.0L frame designs.

 

To be blunt, it's almost as easy to swap in a V-8 (G.M. or Ford small-block, Gen engines and such) as it is to convert a four-cylinder Wrangler to an inline six.  (This is not considering cost, simply the effort involved, Smokie.)  For whatever reason, AMC/Jeep decided to make different frames for the YJ Wrangler four- and six-cylinder inline engine models.  Prior to the Wrangler, the Jeep CJ had bolt-on engine/frame adapters, which at one point could put an Iron Duke G.M. four, a 4.2L six or a 304 V-8 into the same chassis, simply by a change in the bolt-in engine/frame adapters, a bolt-in brace and the right motor mounts!

 

Click here for a MIG welding article I did at the magazine.  In those pictures, you will see what it takes to convert a 2.5L frame into a frame that will accept the 4.0L or 4.2L inline six.  This happens to be my son-in-law's Jeep, an '87 YJ model originally equipped with the AMC 2.5L four.  The rest of the changeover involves use of 4.0L and 4.2L parts, including a bellhousing, the radiator, fan shroud, transmission mounts for the AX15, throttle linkage, air filter system and a list of small parts and hardware. 

 

Since your Jeep is a '95 with the in-tank fuel pump, you would need to deal with the pickup from a 1987-90 YJ Wrangler 4.2L six if the engine swap involves a true 4.2L engine.  That engine is carbureted and if original with an AX15 attached, it's an '89 or '90 application.

 

What I have done with carbureted model year swaps (pre-1991 YJ Wrangler or back to the CJs)  is add the Mopar EFI conversion.  Despite the cost, which has soared in recent years, this can actually make the swap a bit easier.  Mopar patterned the original EFI kit after a '94-'95 Wrangler 4.0L.  You would need the current kit's pressure regulator and fuel pump, since the later Mopar EFI Conversion Kit is actually a single rail design (built around a TJ Wrangler prototype).

 

In my view, you would be making more work for yourself than if you sell your 2.5L and buy a 4.0L model.  You could then consider a stroker 4.6L build at some point if you like the 4.2L kind of torque over the 4.0L inline six.  If emissions is an issue, the 4.2L carbureted engine would be a poor choice in any case, since the last use of carburetion was 1990, and the 4.2L engine is glaringly retrograde for emission purposes.

 

I would opt for a V-8 conversion.  In the long run, an emission legal swap can be done with an LS engine like I filmed at Advance Adapters.  See that HD video for ideas.  The YJ swap would be similar.  This is not a bargain cost-wise, either, but the work is no greater than the 4.2L swap into your 2.5L YJ Wrangler chassis.

 

For others, note that the 1997-2006 TJ Wrangler also uses two frame designs, one for the 2.5L four and the other for the 4.0L inline six.  This creates the same challenges for an engine upgrade.  There are still the radiator, shroud, bellhousing, motor mounts, transmission mount and other differences involved.

 

We can discuss this further and to any degree and detail that is helpful, Smokie.  I value your question, it is of common interest among 2.5L four-cylinder Wrangler owners.

 

Moses



#3 Smokie

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Posted 03 August 2013 - 09:40 PM

I appreciate the information, I have been contemplating a small block ford swap (purely political) as well and I would actually prefer to go V8. The 4.2L w/AX-15 came about when a friend located the 4.2L AX-15 combo and knew I was considering some kind of drivetrain upgrade when my AX-5 went out on me.

 

I'm in the position now that I can either repair the AX-5 I have, replace it with a new "5", swap the AX-5 for an AX-15, my preferred route, or go all in and do the V8 swap. I have the 2.5L and going back to the "5" doesn't set well when I know the "15" would be so much better.



#4 Moses Ludel

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Posted 03 August 2013 - 10:26 PM

Now we're talking!  Though I'm not a die-hard Blue Oval advocate, I have always respected the 351W and the 302 5.0L for their light weight, simplicity and reliability.  The 351W is the better choice for crankshaft stamina, beefier parts and truck use.  For a YJ Wrangler, a smaller journal 302 crankshaft would not be a liability in any case.

 

The problem with the AX5 and AX15 is that they are not interchangeable.  You cannot "bolt-in" an AX15 behind your 2.5L with its bellhousing.  And the four-cylinder engines do not share the 4.0L or 4.2L bellhousing pattern.  You will need Advance Adapter pieces to retrofit an AX15 into your '95 four-cylinder Wrangler behind a Ford small-block. 

 

From what I saw on my filming tour at Advance Adapters in January, they have a way to retrofit the AX15 or NV3550 into the vintage '66-'77 Bronco chassis with a small-block V-8.  I just looked at the website, and the bellhousing did not appear there.  However, this is something we discussed at the plant.  (You can see the extensive HD video coverage at the magazine site.)

 

I suggest a call to Advance Adapters at 1-800-350-2223.  You'd have two questions, and one I'm fairly certain will go your way:  1) Will an '89-'90 AX15 transmission fit to your NP231 transfer case in the '95 (answer should be yes, spline count and clock pattern would be the concerns here) and 2) do they have the motor mounts and a bellhousing to get a small-block Ford V-8 into your YJ with an AX15?  Mention the early Bronco bellhousing for the AX15 or NV3550.  Ask if that would be the bridge.  Share that I suggested you call...

 

Not clear whether you're in an emissions sensitive area.  If so, the Ford 351W and 302 5.0L would need to be 1995-up with MPI.  You'd like that for off-pavement, anyway.  Both engines were available in '95 although close to extinction with the "modular" replacement engines phasing into the Ford equation.  (Do yourself a favor and avoid the Triton engines.)  I would stick with the traditional pushrod 302 or 351W. 

 

Let's continue this dialogue.  Many owners know of the popular G.M. V-8 swaps, especially the late Gen/LS engines.  A 351W or 302 Ford V-8, with distributor at the front, light in weight, the 4WD trucks using a rear oil sump, you have a definite way to go here, Smokie!

 

Another approach that might sound odd would be a Dakota V-8 with an AX15 behind it.  Dakota did use the AX15 and NV3500, the NV231 transfer case, too.  This is starting to sound like a "factory" parts swap with only the engine mounts requiring fabrication.  Why the Mopar 5.2L and 5.9L pushrod V-8s with MPI do not see more swap action is beyond me.  There are factory parts for conversions, the engines are longevity types with ease of service, and the chassis interface would not be that difficult since Chrysler is Chrysler...Any takers?  I like it!

 

Moses





Also tagged with one or more of these keywords: Jeep YJ, Jeep inline six, Jeep 4.2L, AX15, Jeep how-to

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