4.0 head on 258/ or complet 4.0 swap? w/ auot trans?... - JeepForum.com
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Unread 10-31-2008, 09:55 PM   #1
T-$$
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Join Date: Mar 2005
Location: New Hampshire
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4.0 head on 258/ or complet 4.0 swap? w/ auot trans?...

I see a bunch about 4.0 heads and intakes on a 258 block but i haven't seen a ton about jsut dropping in the whole thing. I'd have to assue there would be some mounting issues, or is the 4.0 complete as it is just inferior to the carb 258?

And I know i can search for the answer but a qiuck 1- 10, 1 being the easiest/cheapest , 10 being the trickiest/ expensive, how difficult is the 258-4.0 head swap?

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Unread 10-31-2008, 10:21 PM   #2
Renegade79
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from what i've read, a 4.0 is a direct bolt in replacement for a 4.2 (258). motor mounts, transmission and all. from what else i've read, putting a 4.0 head on a 258 short block requires filling some of the coolant holes on the head with epoxy, but is not all that hard. i believe cjoffroad.com has a complete forum on doing the 4.0 engine and 4.0 head swaps.
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Unread 11-01-2008, 08:36 AM   #3
CJ7Pilot
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You can buy 4.0 HO heads that have already been modified for the 258. It's a pretty easy swap, but you'll need a valve cover, intake manifold and exhaust manifold to fit the 4.0 head.

Is your 258 in good shape? If so, this is probably worth doing. However, if your 258 is approaching time for a rebuild, you'd be much better off swapping in a 4.0 HO (complete with fuel injection).

I did everything in steps: first the fuel injection, then the 258 rebuild, then the 4.0 head swap... and now I really wish I'd just gone for a complete engine swap in the beginning. It would have been cheaper, less time wrenching, and I'd have better performance.

Good luck!
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Unread 11-01-2008, 08:37 AM   #4
gojeepin
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I did mine a little differently than most.

I replaced my tired 4.2L with a 4.0L (carb'd... I like simplicity) and it bolted right in. I really think it's great.

There are a few mods you have to do to make it work but not many...
1. 4.2L intake manifold will mount but you'll need to make some holddown fasteners... the washers are too small.
2. You'll need to modify or fabricate a new power steering bracket to clear the exhaust manifold and extend the length.
3. Mount and wire an electric fuel pump... there's no port for a mechanical pump on the block

Other than that you can pretty much treat it as the same engine. e.g. distributor, MSD 6A, nutter, mounts, trans, clutch, wiring

BTW... I have all the original FI stuff (manifold, injectors, computer, harness) to put the 4.0L if I ever want to.
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Unread 11-01-2008, 09:07 AM   #5
whittlecj
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http://www.jeepforum.com/forum/f8/official-4-0-swap-thread-475002/

Is the official 4.0 swap thread. It has good info as well as links to more. It was on the stickies FAQ page.


I am in a similar phase - tired 258 out and apart - now weighing opportunity costs.
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