Results 1 to 15 of 15
  1. #1
    Join Date
    Apr 2002
    City/State
    Arlington, VA
    Scrambler Year
    1982 Stock
    Year Purchased
    2001
    Posts
    337

    4.0 vs 4.2 w/Head swap...which one better?

    Here is a very interesting question I want to pose and see what you guys think.

    Think of this in the following criteria:
    1. Cost
    2. Technical Prowess
    3. Ease of Maintenance

    I have the orignal 4.2L with a 4.0 Head conversion, TBI, Clifford Heated Intake, Borla exhaust, MSD, Ford TFI setup in my jeep to start so consider this while we go forward.

    Do you think it would be better to do a complete rebuild exactly as it sits or swap in a rebuilt 4.0.

    Now...before you go on...Also to note that because I have a 4.0 intake and exhaust already, the TBI would transplant directly onto this and require absolutely nothing different.

    Basically, for this setup we are talking a rebult 4.0 vs a rebult 4.2 w/4.0 head...Everything else stays the same...tranny, clutch, exhaust, wiring, TBI injection everything. Simply stated...its a motor swap and that's it.

    What do you think?
    1982 Scrambler
    258 w 4.0L Head
    Howell TBI, Borla Header, Clifford Intake, MSD Ignition, Ford TFI Upgrade

  2. #2
    Join Date
    Apr 2002
    City/State
    NE, IL
    Scrambler Year
    '85 CJ8 Laredo w/MPI
    Posts
    775
    Rebuilding:
    - There are different degrees of "rebuild" and consequently a wide range of cost.
    - Also, the cost to "rebuild" various across the nation (even for the exact same work).

    Do you know what needs to be "rebuilt" on your existing 258 block/4.0 head/TBI?

    4.0 swap:
    - as you might expect, the cost/miles on engine varies from one seller to the next and one state to the next.
    - don't forget to include shipping expense.

    You also forgot to consider the remanufactured route which is buying a remanufactured engine from a company that professionally "rebuilds" engines (e.g., ATK).

    If it were me and time was available to shop around, I'd look for a low mileage 4.0 at a reasonable price that comes complete with wiring harness and computer.

    EDIT: Most importantly, how are you going to use your CJ-8? Do you need horsepower (e.g., V-8)?
    1985 CJ-8 Laredo
    Becoming a little less stock (4.0 HO head, MPI, D44 rear, stereo)

  3. #3
    Join Date
    Apr 2002
    City/State
    Arlington, VA
    Scrambler Year
    1982 Stock
    Year Purchased
    2001
    Posts
    337

    4.0 swap will cost way more I think

    Well, I think a 4.0 is a good option, but in realty will cost much more than I want to go. A good low mileage 4.0 with harness and computer will run about $700-1000. Now I have to do a fuel pump, wiring, cps relocator or pull my tranny and have it machined. I have wiring to contend with. I'll need accessories. And on top of that, I'll have more leftovers like the intake manifold and tbi setup.

    To redo my own motor, i'd have just a need for a basic bore-up. May as well do a valve job while I'm at it and replace the wear points and all gaskets and seals.

    To buy...I'd go with a remanufactured motor directly from a vendor. If I go with a 258, I only need a short block. If I got 4.0..I need the whole thing.


    I don't have time or facilities to perform a swap of proportions...I want to get in and get out. I'm talking about doing this in an afternoon and being done. Motor out, motor in...bolt on the accessories. Done.

    Just motor for motor...no electricals, no fuel injection, no nothing else...motor for motor. 4.0 or 258 with 4.0 head???
    1982 Scrambler
    258 w 4.0L Head
    Howell TBI, Borla Header, Clifford Intake, MSD Ignition, Ford TFI Upgrade

  4. #4
    Join Date
    Apr 2002
    City/State
    NE, IL
    Scrambler Year
    '85 CJ8 Laredo w/MPI
    Posts
    775
    Quote Originally Posted by jmarkel
    To redo my own motor, i'd have just a need for a basic bore-up. May as well do a valve job while I'm at it and replace the wear points and all gaskets and seals.

    I don't have time or facilities to perform a swap of proportions...I want to get in and get out. I'm talking about doing this in an afternoon and being done. Motor out, motor in...bolt on the accessories. Done.
    It's good that your asking around. Here's my logic and 2 cents if it was me....

    FWIW, I don't think doing a "rebuild" of your current setup will be a one-day operation for you (or more appropriately, it's not a one day job for your engine rebuilder).

    In a few hours, you can remove your head and take it to a machine shop for them to do a valve job, deck it and mangaflux and pressure test it. That will cost you probably $200-$300. Then you'll need to reinstall it (figure another $100 for new headbolts and head and intake/exhaust manifold gaskets) and another few hours. This assumes you've pulled and replaced a head before.

    So now you're at $300-$400 and all you have is a "rebuilt head" installed.

    I'm sure "a basic bore-up" while the engine is still installed in your vehicle will be another $400+ in labor and parts. So, now you're at about $800 total.

    Yes, with a complete low mile 4.0, you'll spend more time and money:
    - increasing the fuel pressure (my vote is an old Econoline fuel pump installed inline outside your CJ tank)
    - new clutch (and maybe you'll want to do the the ring gear while it's apart).
    - mounting the computer
    - doing the wiring.

    But just think that everything that has been installed has been designed to work together (block, head, FI, etc.) and how much "newer" everything will be (hoses, belt, etc.).

    Yes, a 4.0 swap is more time and slight more $$$, but then again, it might not be more $$$ once you open your 258 up and your rebuilder starts inspecting components.

    Just my 2 cents.
    Last edited by CJ-8_Jim; 09-08-2008 at 04:40 PM.
    1985 CJ-8 Laredo
    Becoming a little less stock (4.0 HO head, MPI, D44 rear, stereo)

  5. #5
    Join Date
    Jul 2004
    City/State
    Arcadia, IN
    Scrambler Year
    ???/1983
    Year Purchased
    2004
    Posts
    1,322
    Not to confuse the issue more, but isn't there a swap where you use the inner parts of a 4.2 and put them in a 4.0 (crank rods etc)? Basically make a stroker...

  6. #6
    Join Date
    Jan 2004
    City/State
    Rotonda West, FL
    Scrambler Year
    1981
    Year Purchased
    2004
    Posts
    1,303

    4.5 Stroker

    That's what I'm running in mine. You use a 4.0 block and use 258 crank and rods. you use the stock 4.0 pistons on the 258 rods. If you deck the block like you suposed to, you will have to run premium fuel to keep it from spark knocking and pinping. I didn't do that. I just used the thinest head gasket I could find. With that said I run regular unleaded fuel with no knocking or pinging. This combination gives you great low end torque. Personally I don't think I'd ever run a 258 again. the 4.5 stroker is too easy of a build.
    But if you want to do the in and out in 1 day, you'll have to buy a complete engine assy which will run you about $2500, for a complete rebuilt motor.

    My 2 cents

    Don
    Hope to get another one someday soon

  7. #7
    Join Date
    Nov 2003
    City/State
    Goose Creek, SC
    Scrambler Year
    1982 Auto 258
    Year Purchased
    2003
    Posts
    2,312
    My first question would be why you think you need to do a rebuild? Smoking when you take your foot of the gas, low cylinder compression, over all poor performance? Each sympton indicates a different problem, not all of which requires a complete rebuild. If it's just because of age/mileage on the engine but it is still running strong, you are probably wasting time.

    Heads can easily be freshened up at home. Unless severely burnt, valve seats can be manually lapped, magnaflux isn't required on a known good head, and valve springs can be easily replaced by borrowing a spring compressor from Autozone or such. Total cost should be under $100 and done in a few hours.

    Unless you have deep scouring in the cylinder walls, if you feel you must, pull the pistons and do a minor honing job then reinstall. New rings, possibly new crankshaft bearings and you should be good to go. All for a few hours work and another $100.

    I'm was raised on a part-time farm where we didn't have the money/time for unnecessary work but still needed things to be reliable. Was nothing for us to pull a motor Friday after dinner and have it back together by Sunday night. Once in a while a head was beyond our ability and had to go to the shop, but not very often. Everyone now-a-days thinks only a shop is qualified to rebuild heads or such so they have forgotten or don't want to mess with the simple stuff.

    On which way to go, from the sound of it, you are happy with your existing setup, so why worry about changing the block and possibly introducing a different porblem. Not to mention the additional cost and headaches of trying somehting new.
    Scrambless
    02 Grand Cherokee

  8. #8
    Join Date
    Apr 2002
    City/State
    Arlington, VA
    Scrambler Year
    1982 Stock
    Year Purchased
    2001
    Posts
    337

    never before

    Well, I've done all sorts of things to this jeep...all work has been done by myself except pulling the axles and putting in new glass.

    I have never broken down a motor before. I pulled the 4.0 head from the yard and sent it to be rebuilt, but I did do all the installation and sealing of the waterjackets. I installed the FI, i've dropped the tranny for a new clutch. Its not like I can't do it...its the time factor... i work long hours and have a baby on the way.

    My jeep is reliable as is, runs pretty good, but does have a good deal of blowby.

    Here is a good question then....can you replace the rings while the motor is in the jeep?
    1982 Scrambler
    258 w 4.0L Head
    Howell TBI, Borla Header, Clifford Intake, MSD Ignition, Ford TFI Upgrade

  9. #9
    Join Date
    Nov 2003
    City/State
    Goose Creek, SC
    Scrambler Year
    1982 Auto 258
    Year Purchased
    2003
    Posts
    2,312
    Here is a good question then....can you replace the rings while the motor is in the jeep?
    Blowby or smoke on deceraltion? Blowby requires rings, smoke on deceralation requires new valve guides. Vavle guides can be done without removing the heads.

    On a stock vehicle it may be a bit hard due to clearance issues between the pan and the axle. A highly lifted vehicle would be a lot easier. Stock I think I would pull the motor as it isn't that hard if you can borrow an engine hoist and stand.

    Just pull the head, drop the pan, disconnect the connecting rod, push the piston out the top, hone the cylinder, install new rings, reinstall piston, reconnect the connecting rod, repeat 5 times, reinstall the pan, reinstall the head and your done. Extremely simple.

    Of course, take this with a grain of salt. While I know how to do it (guess I listened and helped my father more than I realized when I was a kid ) it has taken me almost three weeks to change a radiator out in my Grand Cheorkee.
    Scrambless
    02 Grand Cherokee

  10. #10
    Join Date
    Aug 2004
    City/State
    Richmond, VA
    Scrambler Year
    1981
    Year Purchased
    2004
    Posts
    784
    If it were me I would pick up another 258 (post around and you probably find a freebie) and have it rebuilt professionally just how you want. When it is finished I would pull and swap with what is in it now. Should be doable in a day or over a weekend.
    Richard

    62 Willys SW
    63 CJ6
    67 M715
    69 Commando
    74 Wagoneer Custom
    79 Cherokee Chief
    81 Scrambler
    86 CJ10A

  11. #11
    Join Date
    Apr 2002
    City/State
    Arlington, VA
    Scrambler Year
    1982 Stock
    Year Purchased
    2001
    Posts
    337

    this could be the ticket

    I think I like grantshires suggestion.

    Its definitely blowby...it doesn't smoke at all...but oil likes to come out my valve cover grommets and oil cap.

    If I could remove the oil pan without issue and take off the front clip, I could probably hone and rering this sucker in a weekend without too much issue.

    That would definitely be the cheapest route. My jeep has about 80k miles on the original motor stuffs, 40k on my head swap, and about 5k on my TBI.
    1982 Scrambler
    258 w 4.0L Head
    Howell TBI, Borla Header, Clifford Intake, MSD Ignition, Ford TFI Upgrade

  12. #12
    Join Date
    Aug 2003
    City/State
    Manassas, Va
    Scrambler Year
    1983
    Year Purchased
    1993
    Posts
    3,820
    If you decide on a rebuilding another 258 I might know where a free 258 is, if he still has it.

    Truck
    Military/Exmilitary/Retired? come see us at www.militaryjeepers.com
    83 Scrambler, bought in 94, basically stock except full hard top, 32" tires, bumpers and nerfs..."we can rebuild him" Now in pieces all over the garage
    82 Scrambler, bought in 05, chevy 305, TH350, 205 t-case, 9" rear
    86 CUCV Maintanance truck w/12KW PTO driven generator & air compressor
    83 Scrambler-151/T176/D300...basically stock..possible restoration for DD duties
    81 Scrambler (bought in 2012, built by Crossbones) -Vortec 350/TH350/twin sticked D300/E-Locked D44s/35 tires

  13. #13
    Join Date
    Aug 2004
    City/State
    Richmond, VA
    Scrambler Year
    1981
    Year Purchased
    2004
    Posts
    784
    Quote Originally Posted by Truck
    If you decide on a rebuilding another 258 I might know where a free 258 is, if he still has it.

    Truck
    I love it when a plan comes together! Go get the 258 and have at it.
    Richard

    62 Willys SW
    63 CJ6
    67 M715
    69 Commando
    74 Wagoneer Custom
    79 Cherokee Chief
    81 Scrambler
    86 CJ10A

  14. #14
    Join Date
    Aug 2003
    City/State
    Manassas, Va
    Scrambler Year
    1983
    Year Purchased
    1993
    Posts
    3,820
    Quote Originally Posted by Truck
    If you decide on a rebuilding another 258 I might know where a free 258 is, if he still has it.

    Truck
    My buddy just got back to me and he already got rid of the 258. He said if he would have known a month ago

    Sorry, I do know of a 4.0 out of a XJ complete with computer for $150.

    Truck
    Military/Exmilitary/Retired? come see us at www.militaryjeepers.com
    83 Scrambler, bought in 94, basically stock except full hard top, 32" tires, bumpers and nerfs..."we can rebuild him" Now in pieces all over the garage
    82 Scrambler, bought in 05, chevy 305, TH350, 205 t-case, 9" rear
    86 CUCV Maintanance truck w/12KW PTO driven generator & air compressor
    83 Scrambler-151/T176/D300...basically stock..possible restoration for DD duties
    81 Scrambler (bought in 2012, built by Crossbones) -Vortec 350/TH350/twin sticked D300/E-Locked D44s/35 tires

  15. #15
    Join Date
    Jan 2003
    City/State
    Yorktown, Va
    Scrambler Year
    81' 4cyl, 85' 6cyl
    Year Purchased
    02-05'
    Posts
    3,100
    I got an extra set of 4.0l stroker pistons for $250 if you want them.

    They are Silvolite standard 4.0 pistons that have been milled to lower compression. This way you can run regular pump gas and not orry about pinging.

    When you do the rebuild by the Re Ring kit as opposed to the complete rebuild and give these to the machine shop to install on the rods.

    I am willing to throw in a 258 crank and rods for $50 if you want.


    Carl
    Projects:
    81' CJ-8, 85' Rust bucket, 84' CJ-7 frame off, 81' Project
    Driveable: 01'-TJ Sport

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