Frame Swap: '87 4.2L to '95 2.5L

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YJAllDay

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Reaching out for some expertise here. If something about this has already been posted, I searched, but didn't find it. I have a 1995 2.5L Yj with a bad frame. I plan to replace this frame with one from a 1987 4.2L.

#1: Are there any reasons this cannot be done or any reason I should avoid it? I know there will be changes to the engine mounts.

#2: Any advice on how to tackle this before jumping in blind?

Thanks in advance. These forums are extremely valuable, and I appreciate the help. If all works out, I'll update this thread on the build progress.
 
I see no real reason why it couldn't be done. If it were me, I'd grab a 4.0 & transmission and make the swap rather than chopping off the mounts to convert them to the 2.5 setup. But understood that could be quite expensive. I don't think you'll have any other issues, everything as it relates to the frame is about the same over all the years. Make sure the skid plate nutserts are in good condition and can be torqued to 50ish with anti-seize without breaking or aren't already broken. That can be a real problematic point on these Jeeps depending on where they live and how they were treated.

As for advice, it should be pretty straightforward as a swap. Park it in a spot that's easy to work on. Go through and pull all the wiring harnesses. Engine harness runs down passenger side of engine down to the starter, then to transmission/transfer case and then over to the left frame to go to the fuel tank & pump, so make sure you free that up and pull it up out from under the hood. I would get the old Jeep in the air, move the suspension/axles over to the new frame so that it's a rolling chassis, then just move stuff over one by one. If you choose to cut and weld new motor mount horns, I would probably set the transmission on the skid plate where it needs to go and then place the horns where needed before welding. Make sure you keep the transmission mount oriented in the same set of slots on the skid plate. There is a forward set of slots and a rearward set. I believe the 4.0 uses the rear and the 2.5 uses the front. Reuse whatever it's set in now so that it stays the same later.

Good luck, curious to see how it goes.
 
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Don’t be afraid of the 4.2 either. It’s what is going back in my 89. It seems that a lot of guys anymore are afraid of carburetors, but I have messed with them for so long it is a none issue. I also wonder how long affordable electronics will be available for the 4.0. I ran into this on an Opel and a Cosworth Vega. Working used computers were going for $800 to $1000 in the early 80’s. That was an incredible amount of money at the time. On the low end, both the 4.0 & 4.2 perform nearly the same on torque and horsepower. I don’t know about you, but the lower RPM’s is where I do almost all of my off roading. I just ditched the factory comp. cont. carb for a Weber and eliminated anything that was no longer needed.
 
machoheadgames said:
I see no real reason why it couldn't be done. If it were me, I'd grab a 4.0 & transmission and make the swap rather than chopping off the mounts to convert them to the 2.5 setup. But understood that could be quite expensive. I don't think you'll have any other issues, everything as it relates to the frame is about the same over all the years. Make sure the skid plate nutserts are in good condition and can be torqued to 50ish with anti-seize without breaking or aren't already broken. That can be a real problematic point on these Jeeps depending on where they live and how they were treated.

As for advice, it should be pretty straightforward as a swap. Park it in a spot that's easy to work on. Go through and pull all the wiring harnesses. Engine harness runs down passenger side of engine down to the starter, then to transmission/transfer case and then over to the left frame to go to the fuel tank & pump, so make sure you free that up and pull it up out from under the hood. I would get the old Jeep in the air, move the suspension/axles over to the new frame so that it's a rolling chassis, then just move stuff over one by one. If you choose to cut and weld new motor mount horns, I would probably set the transmission on the skid plate where it needs to go and then place the horns where needed before welding. Make sure you keep the transmission mount oriented in the same set of slots on the skid plate. There is a forward set of slots and a rearward set. I believe the 4.0 uses the rear and the 2.5 uses the front. Reuse whatever it's set in now so that it stays the same later.

Good luck, curious to see how it goes.
Click to expand...
machoheadgames, thanks so much for your insight. I apologize for the delay. I could have bet that I had already typed up something to reply weeks ago, but I'm not sure what happened. You're correct about the expense of the 4.0 setup; if I was looking at spending more, I'd consider that. I'll use what I have for now and enjoy what little power the 2.5 has. My main concern is differences on the frames when mounting everything from the '95 to the '87 frame. It got me concerned when the 2.5L engine mounts are only listed for 1991 - 1995, but I'd say that's because that's the years the 2.5 was used, not on an original 1987, so I'm probably ok. I'm ordering new body mounts and engine mounts. The swap will start in about 3 weeks. If there are any differences, I hope they are minor.

Again, I appreciate your input, and I'll update everyone later. Anything else you may think of that could help me in this, I'm listening.
 
YJAllDay said:
ytradio, thanks so much for your insight. I apologize for the delay. I could have bet that I had already typed up something to reply weeks ago, but I'm not sure what happened. You're correct about the expense of the 4.0 setup; if I was looking at spending more, I'd consider that. I'll use what I have for now and enjoy what little power the 2.5 has. My main concern is differences on the frames when mounting everything from the '95 to the '87 frame. It got me concerned when the 2.5L engine mounts are only listed for 1991 - 1995, but I'd say that's because that's the years the 2.5 was used, not on an original 1987, so I'm probably ok. I'm ordering new body mounts and engine mounts. The swap will start in about 3 weeks. If there are any differences, I hope they are minor.

Again, I appreciate your input, and I'll update everyone later. Anything else you may think of that could help me in this, I'm listening.
Click to expand...
2.5 was used 87-95. It was throttle body injected 87-90 and fuel injected 91-95. The 2.5 uses a different passenger frame horn than the 4.0/4.2 use.
 
ytradio said:
Don’t be afraid of the 4.2 either. It’s what is going back in my 89. It seems that a lot of guys anymore are afraid of carburetors, but I have messed with them for so long it is a none issue. I also wonder how long affordable electronics will be available for the 4.0. I ran into this on an Opel and a Cosworth Vega. Working used computers were going for $800 to $1000 in the early 80’s. That was an incredible amount of money at the time. On the low end, both the 4.0 & 4.2 perform nearly the same on torque and horsepower. I don’t know about you, but the lower RPM’s is where I do almost all of my off roading. I just ditched the factory comp. cont. carb for a Weber and eliminated anything that was no longer needed.
Click to expand...
ytradio, thanks for that. Carbs aren't something that scares me much; I've tinkered enough to take the challenge, but I'm trying to use what I already have. I think it would be a good thing to have the 4.2 carb setup, but for now, it's squirrel power in my 2.5. Good advice on the computers, too. I like the thought of having a purely mechanical and electro-mechanical rig independent of computers. If something ever wipes out those computers, you'll still be rolling.
 
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