Jump to content

Swapping a Jeep YJ Wrangler 4.2L Engine Into a TJ Wrangler 2.5L Chassis


Recommended Posts

I have a 1990 wrangler 4.2l and a 1997 wrangler 2.5l  The 4.2l has modifications that make it put out far more horsepower and torque than the 2.5 and I want to swap out engines and want to know what all I will need to do to make this possible The 97 has a 5 speed and the 90 model has an auto and I would like to bolt the 5 speed up to the 4.2l in the 97 any input and advise will be greatly appreciated                                                                                  thanks   Michael41064  

Link to comment
Share on other sites

  • Administrators

Welcome to the forums, Michael!  Here's the rundown on what you face with this swap...

 

1) If emissions are an issue, the 4.2L, especially if still carbureted, would be a retro engine and not acceptable for emission compliance in states with smog inspection.  If you have a Mopar EFI conversion (preferably a second generation system with single rail FI patterned after the '97-up TJ Wrangler), you might be able to get by with an inspector willing to ignore (or ignorant of) the earlier 4.2L long block versus a 4.0L engine.  This would still be an engine change from four- to six-cylinder, which requires a smog referee station in California.

 

2) The 2.5L bellhousing pattern is entirely different than the 4.2L.  (See my article at:  http://www.4wdmechanix.com/YJ-&-TJ-Jeep-Wrangler-Clutch-Replacement.html.  This is a 2.5L with AX5 transmission in a 1987-90 YJ Wrangler.)  You also have an AX5 manual transmission in the '97 TJ, which was only used with 4-cylinder engines.  This is an issue, as the AX5 will not work with the AX15 bellhousing, so you'll be seeking an AX15 transmission and bellhousing.  The flywheel for the 2.5L could work with your 4.2L crankshaft, I've used a resurfaced 2.5L flywheel on a 4.0L engine.  You'd need the correct pilot bearing for the 4.2L crankshaft and use of a manual transmission.

 

4) The real kicker is the frame.  Both the Jeep YJ Wrangler and Jeep TJ Wrangler use a different frame for the 2.5L engine versus the inline six-cylinder 4.2L or 4.0L engines.  At the magazine, I show what it takes to modify the frame and install a 4.0L or 4.2L in a YJ Wrangler originally equipped with the 2.5L inline four: http://www.4wdmechanix.com/MIG-Welding.html.  The same principle applies with a TJ Wrangler's 2.5L four versus 4.0L inline six-cylinder frame.

 

Aside from the emissions legality issue, unless you have welding and fabrication skills, this could be a major project.  The difference is the location of the side/front motor mounts.  The 2.5L frames have the mounts permanently welded further back on the frame rails.  Whether this was an engineering upgrade or for ease of production, the two-frame production method is somewhat puzzling.  On CJs, the inline 4-, inline 6- and V-8 engines could be accommodated with factory bolt-in frame/engine brackets and even a cross brace bar that bolted into position.  Beginning with the YJ Wrangler, AMC/Jeep adopted the four- and inline six-cylinder frame approach.  Chrysler continued this approach through the Jeep TJ Wrangler era.

 

As a point of interest, the welding and fabrication that you see in my article is overkill compared to the OE frame brackets.  The basic brackets are Advance Adapters products, the additional, reinforcing steel plate is by yours truly.  The vehicle is my son-in-law and daughter's, and I wanted the mounts and welding to be indestructible for off-road, hard four-wheeling.  Welding process is MIG, in this case with ER70S-6 0.035" wire.

 

Trust this helps clarify, Michael...

 

Moses

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...