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F134 Overbored?

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

  1. Jul 6, 2007
    Shawn M

    Shawn M Member

    West Seattle
    Joined:
    Jun 7, 2006
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    51
    I'm looking at a high price rebuild anyway. The block although in good shape is tired. There's a laundry list of work. Sleeves wouldn't be much more, I needed new pistons anyway.
     
  2. Jul 6, 2007
    Mark Mann

    Mark Mann Kermit

    Huntsville, AL
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    Jan 8, 2003
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    140
    Seems to me that increased bore diameter and/or shaving the head would increase compression for the reasons that McRuff mentioned. Cramming a greater air/fuel volume into a smaller combustion chamber.

    As far as the over heating, I think of it like this: metal (in this case) is a conductor and as such the more that is present the greater the ability to "sink" the heat away from the source area. I agree that this is arguably a counter-intuitive point. Just the way I tend to view the problem.

    Newton's law of heating/cooling indicates that less metal is easier to cool- I assume the limit on this is the structural integrity of the block.

    Is there a thermo-dynamists in the house? Very interesting question. :rofl:


    As for my $0.02, I'd likely sleeve it-


    MM :flag:
     
  3. Jul 6, 2007
    Rondog

    Rondog just hangin' out

    Parker, CO
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    I'd have 'em bore it until the cylinders clean up, then get pistons to fit, rather than starting with .080 pistons. Going from .030 over to .080 is a huge leap, you'd have to have some serious pitting to bore out .050 in one shot. A competent engine builder shouldn't have any problem taking it to .040 first, then to .050, then .060, etc., until the bores are good. I certainly wouldn't go to .080 or sleeves unless absolutely necessary.
     
  4. Jul 6, 2007
    Shawn M

    Shawn M Member

    West Seattle
    Joined:
    Jun 7, 2006
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    51
    the top inch or so is beat to hell. It sat for long periods of time and was the victim of crappy shade tree rebuilding. As for what exactly is going to make it, I'm not sure. They say they're pretty sure it's going to 080 and I do tend to listen to these guys. They specialize in the exotic, high dollar, european, classic and antique. They love the unusual and have been very successful. I am giving lots of thought to sleeving. I'm going to the shop today to talk to them about it.
     
  5. Jul 6, 2007
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Aug 10, 2003
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    Yep, that's right. You should buy the parts after the machining is done. Don't burn your bridges till you come to them.

    No experience with the F134, but I've heard the 80 or 100 over pistons are available. Those old castings were very heavy because the casting technology was inferior to todays. This means the core shift could be a lot larger than you'd expect today. If you need to go over the factory maximum, you can either sleeve the bad cylinders or sonic check to see that there wasn't a lot of core shift. If the core is well centered, there should be plenty of iron in the walls. You can also sleeve just one cylinder if there's a particularly bad one.

    I would guess that 80 over is going to be fine.
     
  6. Jul 6, 2007
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    I'm not a physicist, but I play one at work (my job title is physicist, but I'm really an engineer). I think the issue with the thin walls is conduction into the coolant. There are only two paths really for heat to leave the engine - coolant and exhaust. I would guess that a lot of the heat of reaction goes out with the exhaust gases. A thin spot in the cylinder wall would tip the balance from the exhaust to the coolant, lowering the exhaust gas temperature and raising the coolant temperature. Just speculation.

    It could also be an issue with local hot spots causing vaporization of the coolant. Water vapor has a lot lower heat capacity than liquid water, and this could seed a coolant chain reaction, where the lower heat capacity of the gas bubble leads to a larger gas bubble, etc. I like this theory better.
     
  7. Jul 6, 2007
    Shawn M

    Shawn M Member

    West Seattle
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    I wanted to get some pictures here but the wear doesn't show up well. The pitting is deepish below the lip worn into the cylinder wall. The piston wear is deep, 030 near the top to 050 beneath the wear lip. The pitting may take that further, possibly to 080. Looks like it was driven alot and then sat for a while with moisture in the combustion chamber. None of the rust is recent, it's very dark and the edges of the pits are rounded so it was driven with the rust in there. They're going to bore it out to where ever they need to and then we'll make a determination. I suggested sleeves to the machinist. He seemed very confident I wouldn't need them. I'm also thinking about raising the compression ratio to 7:1 or maybe a tiny fraction higher like 7.4:1.
     
  8. Jul 7, 2007
    tomcam

    tomcam Member

    Savannah Tn.
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    Jul 31, 2005
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    89
    I have a F134 bored .80 becasus of a broke oil ring when i put the engine back togther after break in I cant tell any difference in cooling or preformance
    but i didnt do anything to the head I had to go fron .20 to .80 to cleane up the gash in the #1 bore
     
  9. Jul 7, 2007
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Sounds like a good plan to me! Let us know how it turns out. :coffee:
     
  10. Jul 8, 2007
    ktm25089

    ktm25089 Member

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    Oct 18, 2006
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    and what are the safety limits for sleeving the crankshaft?.60 is too small?i use my jeep for small trips and fun.no hard use at all.

    thank you
    george
     
  11. Jul 9, 2007
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Please start a new topic for this question.
     
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