Put a 4.0 in my cj5!!? - JeepForum.com
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post #1 of 4 Old 01-10-2014, 08:25 PM Thread Starter
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Put a 4.0 in my cj5!!?

I have a 74 cj5 and recently tore the engine down for a rebuild as it has been ran out of oil in the past, had coolant in the oil and timing chain about to rub through the cover. I took all the parts to the machine shop and a back to factory-ish rebuild is going to cost me about 1400 with a new carb. I was looking to get it on the road in the meantime and was looking for a used engine. The best I've come across is a 4.2 that has sat for 10 years but "ran" when put away. I can get it for two hundred. Being a tech I would want to re ring it at least and put new bearings in and that's another two hundred. I see far more used 4.0s how much work is it and what would need to put a 4.0 in my cj5? Would it work with my three speed trans?

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post #2 of 4 Old 01-11-2014, 10:13 AM
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1978 CJ5 
Join Date: Sep 2009
Location: Norman, OK
Posts: 130
Yes, you can keep your 3 speed. But check out novak or advanced adapters. One of them will modify the bellhousing for the CPS.

You'll need working harness and pcm with most of the stuff disabled. (Either a retune or a stand alone system(505 performance has a kit I believe))

You'll need a fuel system over haul. Depending on the year of your donor engine they will run on different pressures.

Other than that it should be similar to replacing the engine with what you have.
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post #3 of 4 Old 01-11-2014, 03:56 PM
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1977 CJ5 
Join Date: Apr 2009
Location: Arlington TX
Posts: 884
You can swap on a cj intake and run a carb. You don't have to use FI if you don't want to. That being said if you want FI hesco would have everything you need. They have a crank relocation kit which moves it to the balancer so you dont have to drill your bellhousing and a harness if you don't want to pull it from the donor vehicle. There would definitely be more work involved in a swap but has been done many times and there is a 4.0 swap thread in the cj forum.
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post #4 of 4 Old 01-11-2014, 10:19 PM
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1984 XJ Cherokee 
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if you have a decent machinist and the plan to build an engine I'd go stroker. Get a decent 4.0 block and the HO head and use your 4.2 crank/rods. If you stay carb so be it, but efi would bring benefit with the work. I just bought another xj with blown engine and sourced a 4.2 rotating assembly. I'm about 2k into the whole setup and its a decent bump of fun with a little more displacement and a cam. I thought of stock 4.0 again, but for the extra 500 for crank and cam( since machine work was a given) it was totally worth the dollar. Also a tech at a local shop so resources for parts were easy. Happy building!

84 xj 350tbi, sm465, 203/205, 60/70. links and other junk.
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