1. #1
    TerryMason's Avatar
    TerryMason is online now Administrator
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    Six Cylinder 4.2 Liter Jeep engine Specs

    The popular AMC 258 inline 6 4.2L engine was introduced back in 1971, and was used in various pickups and Wagoneers. In 1972 the engine was avaliable in Jeep CJs, and eventually made it's was into Wrangler YJs until it was phased out. This engine produced gobs of torque, was reliable, and inexpensive.

    The carburetor (Carter BBD) that was chosed for this system, and it soon became very unpopular. It used a pulse air system that was a mess of air hoses.
    Last edited by TerryMason; 01-27-2008 at 11:58 AM.

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    Six Cylinder 4.2 Liter Jeep engine Specs - Technical specs

    Displacement256 cubic
    inches


    Click below to see
    the Vacuum curve


    Cylinder numbers (front
    to rear)
    1-2-3-4-5-6
    Firing order1-5-3-6-2-4
    Spark Plug gap0.033 to
    0.038
    Ignition timing9 to 11
    degrees
    Idle speed (auto)600 +/-
    70 rpm

    (manual)

    680 +/-
    70 rpm
    Engine oilAPI SE of
    SF
    - Oil capacity6qts
    Automatic
    Transmission Fluid
    Mercon
    ATF
    - ATF Capacity4qts


    EngineTransmissionInitial
    Timing at


    Curb Idle (Vacuum
    Hose

    Disconnected)

    Curb
    Idle Speed RPM

    Set
    To
    Acceptable

    Range
    Set
    To
    Acceptable

    Range
    258

    1 Barrel carb
    Manual

    (49)



    850

    (49)
    750

    950
    10°

    (Alt)


    12°
    600


    (Alt)
    500

    700


    (Cal)


    10°
    850

    (Cal)
    750

    950
    Automatic

    (49)


    10°
    550

    (49)
    450

    650
    10°


    (Alt)


    12°
    550

    (Alt)
    450


    650


    (Cal)


    10°
    550

    (Cal)
    450

    650
    258


    2 Barrel carb
    Manual


    650550

    750
    Automatic



    550450

    650

  3. #3
    ricroz's Avatar
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    Re: Six Cylinder 4.2 Liter Jeep engine Specs

    Coverted my 1986 AMC Eagle to Howell TBI fuel injection last year. Ended up with a much better running engine and a garbage can full of useless hoses and emmisions control junk. I understand AMC was about to move all it's cars to FI when the company folded in 88.

  4. #4
    carnuck's Avatar
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    Re: Six Cylinder 4.2 Liter Jeep engine Specs

    They had TBI in '86 (My Comanche 2.5L has it) and were about to put it into the Eagle SX4s but when Chrysler took over, they nixed the idea and designated the AMC version of the Eagle to the trash pile, then sold the name to Eagle Mitsubishi a couple years later.

    The AMC 6 cyls had 2 different bell patterns that changed in '72 to match the AMC V8s. Prior to that they had their own small pattern and '71 is the only year for 258s with the small pattern (they lived on in Industrial use and Postal trucks a few years more)

    In '71 the block was made taller for a longer stroke. The 258 is the early 232 with a longer stroke. The '71 up 232 is a 199 with longer stroke. They did the same thing with the V8 motors.
    343 became 360, 290 became 304 and 390 came out, they modified the block (extra webbing and beefing up) to make the 401.

    The 258 had 2 other relatives besides the 232. In Mexico they had a 282 and a 262 made by making the bore larger (new block)

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    Re: Six Cylinder 4.2 Liter Jeep engine Specs

    Yuk! I have the 258 I-6... I went witrh the offenhauser intake mani, Holly truck avenger (I jetted it down to about 270) pacesetter headers with magna flo exhaust. It now runs like a raped ape I love it!

  6. #6
    Buck hour's Avatar
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    Quote Originally Posted by DIRTY-CJ
    Yuk! I have the 258 I-6... I went witrh the offenhauser intake mani, Holly truck avenger (I jetted it down to about 270) pacesetter headers with magna flo exhaust. It now runs like a raped ape I love it!
    How much was the avenger and where did you get it from?

  7. #7
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    Re: Six Cylinder 4.2 Liter Jeep engine Specs

    I have a question about the 4.2L I6. I noticed TerryMason posted specs for auto and manual trannies for that engine. Does anyone happen to know what automatic transmission bolts to that. I have a 1990 Wrangler YJ. Tranny went out and all i am finding are manuals. Any info would be great! THANKS

  8. #8
    elevatorman's Avatar
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    Re: Six Cylinder 4.2 Liter Jeep engine Specs

    Chrysler TF 999.
    I have a 1987 and my buddy has a 1990 . Both are automatics and both have the same trans.
    I had done some research last year and this is the one that was listed. Used mostly by Chrysler in medium sized trucks and jeep

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