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F134 Overbored?

Discussion in 'Early CJ5 and CJ6 Tech' started by Shawn M, Jul 5, 2007.

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  1. Shawn M

    Shawn M Member

    Exactly how far can I bore a F134. At some point a previous owner bored to 030, which is fine by me, but he also left the jeep sitting for a long time. The bore is pitted near the top. and needs to go 080 over. Can this be done safely?
     
    Shawn M, Jul 5, 2007
    #1
  2. Glenn

    Glenn Kinda grumpy old man Staff Member

    Mine is .060 over, which I've heard is maximum so I don't know about .080. Have you considered sleeves?
     
    Glenn, Jul 5, 2007
    #2
  3. Shawn M

    Shawn M Member

    I"m thinking about them. My machinist says the 080 over won't be a problem due to the very thick casting.
     
    Shawn M, Jul 5, 2007
    #3
  4. Glenn

    Glenn Kinda grumpy old man Staff Member

    I've heard that too. Was kind of torn about going to .060 on mine.
     
    Glenn, Jul 5, 2007
    #4
  5. Shawn M

    Shawn M Member

    I should have a talk with my machinist about just how I intend to use my Willys. I don't want anything flexing or whatever nasty thing I don't want to think about.
    Is 080 over going to reduce my already low compression ratio?
     
    Shawn M, Jul 5, 2007
    #5
  6. Mcruff

    Mcruff Earlycj5 Machinist

    Overboring will increase compression not lower it. By boring you are increasing the volume that you are cramming into the head chamber, therefore increasing compression. Minimally but none the less you are increasing it, not decreasing it.
     
    Mcruff, Jul 5, 2007
    #6
  7. Glenn

    Glenn Kinda grumpy old man Staff Member

    No it won't change the compression ratio. If the head is shaved at all the ratio will actually increase.
     
    Glenn, Jul 5, 2007
    #7
  8. w3srl

    w3srl All-around swell dude Staff Member

    The biggest risk with overboring is overheating, not flexing. There is a LOT of iron in that block! Before I'd go .080 over though, I'd investigate sleeves. YMMV. ;)
     
    w3srl, Jul 5, 2007
    #8
  9. Shawn M

    Shawn M Member

    Overheating because of having a bigger fire? The cooling surface area doesn't change. If the bigger fire is big enough to cause overheating, won't it also change my gas mileage?
     
    Shawn M, Jul 5, 2007
    #9
  10. w3srl

    w3srl All-around swell dude Staff Member

    NO, overheating due to more surface area inside the cylinder to absorb heat, and the same amount of surface area OUTSIDE the cylinder to shed the additional heat.
     
    w3srl, Jul 5, 2007
    #10
  11. Glenn

    Glenn Kinda grumpy old man Staff Member

    I have always assumed that the thinner the cylinder wall the more that heat is able to radiate through the wall and be absorbed into the cooling water, also causing overheating, or running warmer at least.
     
    Glenn, Jul 5, 2007
    #11
  12. Shawn M

    Shawn M Member

    How much should I worry about the F134 over powering the stock radiator? I didn't have a lot of time driving the jeep, but I did drive it a few hours on a nice sunny warm day with the needle near the bottom of the temp range.
     
    Shawn M, Jul 5, 2007
    #12
  13. Glenn

    Glenn Kinda grumpy old man Staff Member

    I don't know if there's a good answer to that question, we can only tell you potential problems to consider.
     
    Glenn, Jul 5, 2007
    #13
  14. gasman

    gasman Member

    those blocks had alota iron in them I,ve got an F-head the is .80 over they used to bore chevy small blocks .125 thousent,s over stock.
     
    gasman, Jul 5, 2007
    #14
  15. Shawn M

    Shawn M Member

    Gasman, how do you use your jeep? Have you had any overheating problems 80 over?
     
    Shawn M, Jul 5, 2007
    #15
  16. Glenn

    Glenn Kinda grumpy old man Staff Member

    Another thing to consider however is any corrosion over the years of the water jacket side of the cylinder wall.
     
    Glenn, Jul 5, 2007
    #16
  17. gasman

    gasman Member

    no problem over heating I do a lot of crawling temp stays about 180 oil pressure at 55 Psi I did put a radiator out of a DJ in it 3 ROW . Always slow speed 3 to 5 mph no shroud stock 4 blade fan.
     
    gasman, Jul 5, 2007
    #17
  18. Shawn M

    Shawn M Member

    thoroughly tanked. Clean and pretty
     
    Shawn M, Jul 5, 2007
    #18
  19. Glenn

    Glenn Kinda grumpy old man Staff Member

    Decisions, decisions. :)
     
    Glenn, Jul 5, 2007
    #19
  20. w3srl

    w3srl All-around swell dude Staff Member

    I guess you'd have to weigh the cost of sleeving vs. the cost of possibly having to do it twice. Either way you are looking at the cost of a set of pistons, since you will want to go back to stock specs if you sleeve the block.

    Decisions, decisions!
     
    w3srl, Jul 6, 2007
    #20
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