85 Xj 2.5 swap with a 4.0

I have an 85 XJ 4wd 5 speed. I have just acquired a donor that I bought for the spotless leather interior. After studding the parts that I needed I found that it has a good 4.0 and all of the parts that I think I will need. One problem I can see is that I have a 5 speed. Will The 4.0 work with that trans? Also is there any problems to look out for along the way.

Youll need to modify the front clip,the 85's are shorter and will not accept the 4.0(as a bolt-in).

The bell housing bolt pattern on the 4.0L is the AMC V8 pattern. It is larger than the bolt pattern on the 2.5L/2.8L engines, which are the small GM V6 bolt pattern. Also, your 5-speed is probably an AX-5 (might be a T-5). It's a light duty transmission that probably would not live very long behind a 4.0L even if you find a way to get it to bolt up. Input shaft diameter is smaller than the trannies used behind the 4.0L, so you'd be looking at a mixmaster for release bearing and maybe pilot bearing.

Clutch and flywheel are smaller for the 2.5L and 2.8L than for the 4.0L also.

Aside from needing to modify the front radiator supports and nearby sheet metal, most people who have attempted this swap also found that they needed to "massage" the firewall.

In summary -- it is far from a bolt-in swap. I can and has been done, but it ain't easy.

I just went and picked the new XJ up today and it's in much better shape than I thought. I got it for a couple hundred bucks with a clear title. The only problem I have found is the engine. After I washed the mold off I accualy found good paint and only onef ding in the entire body. So all I have now to do is pull the 4.0 and tear it down and swap all of my suspension parts along with all the other mods I have made to my 85. The 2.5 to 4.0 swap seems like more trouble than its worth.

BrazosRiver_XJ said:

I just went and picked the new XJ up today and it's in much better shape than I thought. I got it for a couple hundred bucks with a clear title. The only problem I have found is the engine. After I washed the mold off I accualy found good paint and only onef ding in the entire body. So all I have now to do is pull the 4.0 and tear it down and swap all of my suspension parts along with all the other mods I have made to my 85. The 2.5 to 4.0 swap seems like more trouble than its worth.

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smart choice..

sidriptide said:

smart choice..

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x2

I don't think I did to bad, it's realy clean and I hooked up a battery and all of the electrical system is working, guages, windows,locks, I mean everything. The engine how ever may not be so promising, the plugs have been pulled out and never put back in. From what I have been told it was running when it was parked, but is had gotten realy hot and was parked. Now with the missing plugs there are prob mudd dobbers living in there. I am going to try to pull it in the next few weeks and see if there is anything left. if not I have another 4.0 (block only). So hopefull I will be in business.

If you end up doing the 2.5L to 4.0L swap, back channel me. I did it on an 85 XJ. Too many old wives tales out there about the swap. I can give you first hand knowledge.

I will keep that in mind. I have had my 85 for some time now and I am kinda attached to it. Plus it is trail ready it's just lacking that punch that a 4.0 has. Any way I go I will have to rebuild the engine. Any suggestions as to which kit is the best with out costing a fortune.

I am doing a similar swap with a 96 2.5 taking a 4.0, and our threads may be helpful to each other.