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F Head Bore Diameter

Discussion in 'Early CJ5 and CJ6 Tech' started by NC-69-CJ, Jan 19, 2007.

  1. Jan 19, 2007
    NC-69-CJ

    NC-69-CJ New Member

    Joined:
    Jan 4, 2007
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    12
    I am in the process of tearing down a 69 F Head for a re-build. Can someone verify that the factory bore diameter is 3.125"? I measured the diameter on the engine last night and I measured 3.185" so it sounds like the block has already been bored over .060". Any opinions on the max I should re-bore this engine? I may just hone the cylinders and skip the re-boring as there wasn't a real lip on the cylinder walls and everything else looked OK.

    Tks
     
    NC-69-CJ, Jan 19, 2007
    #1
  2. Jan 19, 2007
    termin8ed

    termin8ed I didn't do it Staff Member

    Mason, MI
    Joined:
    Dec 22, 2002
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    4,422
    sounds right. I've seen .080" over pistons, but not sure who had them. Might have been 4wd hardware. If everything looks good and that was your reading in all cyl, honing would probably be just fine.
     
    termin8ed, Jan 19, 2007
    #2
  3. Jan 19, 2007
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
    Joined:
    Nov 27, 2006
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    2,793
    The Haynes manual has the bore listed as 3.125 to 3.127 in. ( direct quote):)

    The Piston diameter near the bottom of the skirt is 3.1225 to 3.1245 in.
    Max overbore seems to be .040 in. After that it is recommended that you sleeve the poor little thing. This help?:coffee:
     
    1960willyscj5, Jan 19, 2007
    #3
  4. Jan 20, 2007
    NC-69-CJ

    NC-69-CJ New Member

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    tks for the info. has anyone here had any bad experiences with an f head that has been bored .060"?
     
    NC-69-CJ, Jan 20, 2007
    #4
  5. Jan 20, 2007
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Sep 21, 2002
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    My 3B is .060 over. You shouldn't have any problems. It's pretty common to bore that much over.
     
    Glenn, Jan 20, 2007
    #5
  6. Jan 20, 2007
    kaiser_willys

    kaiser_willys Well-Known Member

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    Jan 7, 2007
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    the most common problem would be overheating i am not sure how far this engine can be bored safe,but have seen some bigblock chevys bored 125 thousands,if there is no scars in the cylinder walls good hone job should be alright with castiron rings,moly or chrome rings are good but to me they are too hard and wear the cylinder walls excesivley
     
    kaiser_willys, Jan 20, 2007
    #6
  7. Jan 20, 2007
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
    Joined:
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    If the weather is hot it might tend to run a bit warm but mine has never overheated. Just make sure your cooling system is in good shape.
     
    Glenn, Jan 20, 2007
    #7
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