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Changing 225 Oddfire To 231 Evenfire

Discussion in 'Jeepster Commando and Commando Tech' started by Henry Nachtsheim, Apr 17, 2019.

  1. Apr 17, 2019
    Henry Nachtsheim

    Henry Nachtsheim New Member

    Sanibel
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    I plan on rebuilding my '68 225 this summer or fall, is it possible, or any reason to, change it to 231 evenfire? Could the cam, crank and distributor from an evenfire be used in the 225 block. Also punch it out to accept 231 pistons? What would be the advantage? I live on an island and as a rule don't go much over 45 or 50, go to the Glades some and creep around the Big Cypress. Not really a speed demon.
     
  2. Apr 18, 2019
    fesser

    fesser Napa, CA Sponsor 2019 Sponsor

    Napa, CA
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    I can't answer your questions about what is possible to change but I can offer my personal experience with both the odd 225 and the even 231. I have run both engines in the same flat fender without changing the trans/t-case/axles etc. so the only variable was the engine. The 231's (I burned a piston in one and swapped in another used engine) idled smoother and were easy to locate ignition parts for. The 225 (current engine) has a bit of a lumpy idle. It has far more seat of the pants power, particularly at lower RPM's (don't have numbers to back it up, just how it feels). All of my experience was with used engines, so that could be a variable. Since what you are talking about changing, is basically an engine rebuild, I would keep it all oddfire. More power, same weight, etc. Either way, they aren't too cheap to rebuild and you might want to consider a more modern, more common V6 like the GM 4.3. Probably could get a really decent used one for a lot less than the Buick will cost to rebuild.
     
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  3. Apr 18, 2019
    Henry Nachtsheim

    Henry Nachtsheim New Member

    Sanibel
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    Thanks for the info, something to think about.
     
  4. Apr 19, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

    Medford Mass USA
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    My understanding is the main difference is the crank design. The odd fire is odd because the pairs of rods share the same journal on the crank. To make an even fire, the crank needs 6 separate journals, one for each rod.

    The change to 231 cid was done to align the V6 with the Buick 350 engine line; then both had the same bore. The 225 block will accept 231 pistons if you bore it out to 0.050" oversize and use 0-over 231 pistons. The 231 has only that much larger bore than the 225, and your typical gray iron block from Detroit (like the 225 and 231) will go 60 over routinely. 60-over 231 pistons would give you a 247, but you'd need to sleeve your 225 block at something like $100/hole.

    From a practical viewpoint, I would say it will be vastly easier to find an even fire 3.8L core and build that, if you must have even fire. The 231 will drop in to replace the 225, with proper flywheel rebalancing. There are too many unknowns trying to convert your existing core to even fire, and I see very little advantage to it. I expect the only thing you can't do with an odd fire engine that you can do with an even fire is spark control from the EFI computer. Even that may be possible with the right combination of parts and programming.
     
  5. Apr 19, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

    Medford Mass USA
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    What's your complaint about the 225? Does it use oil? Low compression? The idle note (potato-potato-potato...) is characteristic of these engines and considered distinctive and charming in the right circles.
     
  6. Apr 19, 2019
    Henry Nachtsheim

    Henry Nachtsheim New Member

    Sanibel
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    Burning about a qt of oil every 1000mi and loosing coolant ,not knowing where to, also about a qt every 1000 mi.
    APX 140,000 miles on engine.
    Don't have a problem with the 225, just checking options, actually it pulls like a locomotive, happy to stay with it.
     
  7. Apr 19, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

    Hills of NH
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    Back in the day a quart of oil per thousand miles would have sounded pretty good to me.
     
  8. Apr 19, 2019
    47v6

    47v6 junk wrecker! Sponsor

    Washington DC.
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    140K on the odd fire without a rebuild!!! Wow!!!!!!
     
  9. Apr 19, 2019
    Keys5a

    Keys5a Sponsor Sponsor

    Florida Keys
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    With a true convertable Jeepster, I would keep the 225 odd-fire just to keep it mostly original. You'll likely spend more in parts converting to a 231 even-fire. There was an odd-fire 231 used for a year or two back in '75-'77, and yes, a 225 block can be over bored to use standard size 231 pistons.
    -Donny
     
  10. May 1, 2019
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

    At the foot of...
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    Mine's at 169K and counting.It's never been out of the Jeep.
    (Knock on wood!)
     
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  11. May 3, 2019
    Henry Nachtsheim

    Henry Nachtsheim New Member

    Sanibel
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    Keep on rockin....
     
  12. Jul 4, 2019
    fhoehle

    fhoehle Sponsor Sponsor

    Harford Township, PA
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    Why sound like a lumina or some minivan with an evenfire when you can sound like potato potato potato.

    I am just being funny, I do like my oddfire. If I were in your shoes I'd rebuild it as an oddfire, and address the oiling system as per Tarry's thread on here. No offense to any evenfire, minivan or lumina owners here.
     

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