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Thread: Wanted a 3.9 motor

  1. #1
    Join Date
    Jul 2011
    Location
    NW Va.
    Posts
    20

    Default Wanted a 3.9 motor

    Looking for a 3.9 for my 90RR.
    I have a hole in my block from a thrown rod.
    a whole motor would be great, or a short block.
    ? Could a 4.2 work ?

  2. #2
    Join Date
    Oct 2011
    Location
    Mountains of Western Pennsy.
    Posts
    592

    Default

    A 4.2L would work up to '95 RRC since they have the same computer and a distributor.

    '95 R.R.C. Lwb
    '76 Series III Hybrid 109
    '70 Rover 3500S

  3. #3
    Join Date
    Jul 2011
    Location
    NW Va.
    Posts
    20

    Default

    Is the 4.2 a bored out or a stroked 3.9 ?

  4. #4
    Join Date
    Oct 2011
    Location
    Mountains of Western Pennsy.
    Posts
    592

    Default

    Ok, the 3.9 (and the 4.0) have a 71mm (2.8") stroke and a 94mm (3.7") bore. The 4.2 is also 94mm (3.7") bore but a 77mm (3.03") stroke. So, it's stroked.

    '95 R.R.C. Lwb
    '76 Series III Hybrid 109
    '70 Rover 3500S

  5. #5
    Join Date
    Jul 2011
    Location
    NW Va.
    Posts
    20

    Default

    Cool,
    Will my 3.9 heads work with the 4.2 ?
    Any other accessories transferable ?
    Thanks for the info,
    Tom

  6. #6
    Join Date
    Oct 2011
    Location
    Mountains of Western Pennsy.
    Posts
    592

    Default

    Should all be compatable. If you're putting on new head gaskets, I suggest you use an ARP head stud kit, they're expensive but they take the stress off of the block and hold the head tighter and more even than the "Torque To Yield" head bolts, thus harder to blow head gaskets. Not everyone agrees with this, but I've never done the job twice using head studs (and all my vehicles are V-8's). i also use permatex head gasket sealer spray, also something some don't agree with.

    '95 R.R.C. Lwb
    '76 Series III Hybrid 109
    '70 Rover 3500S

  7. #7
    Join Date
    Jul 2011
    Location
    NW Va.
    Posts
    20

    Default

    thanks,
    the 90RR runs a ZF4HP22 transmission...ok for the 4.2 ?
    got a 4.2 short block laying around ?
    tom

  8. #8
    Join Date
    Feb 2010
    Posts
    151

    Default

    Not a problem

  9. #9
    Join Date
    Jul 2011
    Location
    NW Va.
    Posts
    20

    Default

    anyone of a source for motors ? 3.9 / 4.2... used but rebuildable.

  10. #10
    Join Date
    Nov 2012
    Location
    Baltimore, MD
    Posts
    14

    Default good running 3.9 (120K ish)

    Quote Originally Posted by 94d90va View Post
    anyone of a source for motors ? 3.9 / 4.2... used but rebuildable.

    I have a good running 3.9 out of an 95 RRC I recently converted to Diesel. Take it. It's just sitting in my shop asking for a new home. I still have the truck under construction so you're welcome to come see the vehicle it was removed from.. I've had several of these trucks and my daily driver is a second 95 RRC so I know them very well and this truck and engine are in great condition and are in Downtown Baltimore.

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