1. Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.
    Dismiss Notice

Odd or Even 231?

Discussion in 'Early CJ5 and CJ6 Tech' started by thatch 65, Oct 29, 2010.

  1. thatch 65

    thatch 65 New Member

    I got a hold of a 231. By block casting # it is a 77. Is there any way to tell if it is odd or even fire without checking the crank #? The distributor is not with it.
     
    thatch 65, Oct 29, 2010
    #1
  2. nickmil

    nickmil In mothballs.

    If you don't have the distributor the best way is to check the crank. If every connecting rod has its own journal it's an even fire. If each journal is shared by 2 connecting rods it's an odd fire. '77 was the transition year. First part were odd fires and last part were even.
     
    nickmil, Oct 29, 2010
    #2
  3. Patrick

    Patrick Super Moderator Staff Member

    Why was I thinking it was the other way around?
     
    Patrick, Oct 29, 2010
    #3
  4. nickmil

    nickmil In mothballs.

    Thinking SBC?
     
    nickmil, Oct 29, 2010
    #4
  5. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    I'm no expert on this, but I understood that the simple crank on the odd fire is what makes it odd. A 90 degree V with journals separated by 120 degrees gives an uneven combination of firing angles.
     
    timgr, Oct 29, 2010
    #5
  6. thatch 65

    thatch 65 New Member

    Thank you, I'll pull the pan.
     
    thatch 65, Oct 29, 2010
    #6
  7. alex211

    alex211 Member

    Just pull the distributor cap and see what it is.
     
    alex211, Oct 30, 2010
    #7
  8. nickmil

    nickmil In mothballs.

    Uh, his post says there is no distributor with it. How can he pull the cap to check it?
     
    nickmil, Oct 30, 2010
    #8
  9. alex211

    alex211 Member

    I guess I missed that part.
     
    alex211, Oct 30, 2010
    #9
  10. thatch 65

    thatch 65 New Member

    Odd it is, Thanks everyone.
     
    thatch 65, Oct 31, 2010
    #10
  11. imajeepnut

    imajeepnut New Member

    So there's no way to determine whether it's an "odd-fire" or not unless you pull the pan? Does the firing order change between odd and even blocks...? I was hoping I could tell by that. I just had to replace some fuel lines today and I was wondering what I had in my '71. Someone has already installed a Petronix distributor setup in this one.

    Thanks,
    Jeff
     
    imajeepnut, Nov 1, 2010
    #11
  12. Mcruff

    Mcruff Earlycj5 Machinist

    If you have the distributor you can tell if its oddfire or evenfire by looking at the rotor and point lobes or the stator ring and cap if its electronic. The oddfire and evenfire both have the same firing order. You can also run the serial numbers on the block, if its older than 1975 it can only be an oddfire unless someone has swapped guts out of the motor (unlikely though). 1977 was the transition year between oddfire and evenfire and without the distributor the crank is the only way to tell. Run the casting numbers if the motor is a 71 then its oddfire only.
     
    Mcruff, Nov 1, 2010
    #12
  13. sparky

    sparky Sandgroper Staff Member Founder

    If it has Pertronix it's odd-fire. There weren't points distributors installed in even fire 231s.
     
    sparky, Nov 1, 2010
    #13
  14. Mcruff

    Mcruff Earlycj5 Machinist

    Not sure this would be 100% correct as most marine engines had points long after HEI came out. Don't know when they quit using 231 motors in marine use. Unlikely you would have one in a car but anythings possible.
     
    Mcruff, Nov 1, 2010
    #14
  15. sparky

    sparky Sandgroper Staff Member Founder

    OK, my mistake. I only knew GM was putting HEI in the 231 even fire engines, especially since the OF 231 used HEI and quit using points long before the EF 231. There for I ASSUMED that there were no even fire Buick 231s which sported a points distributor OR that it was a reasonable assumption that if you have a points distributor in a Buick V6 it's a.) a 225, b.) a 231 OF with points, or c.) a 198, all of which are odd fire engines. Glad we cleared that up.
     
    Last edited: Nov 1, 2010
    sparky, Nov 1, 2010
    #15
  16. imajeepnut

    imajeepnut New Member

    I'll run the casting numbers and see. My CJ6 is a 71, and my Jeepster a 69. Both should be original..."should" being the key word there.

    Is there a benefit to having one over the other...odd or even fire?
     
    imajeepnut, Nov 1, 2010
    #16
  17. w3srl

    w3srl All-around swell dude Staff Member

    It's not like we've ever seen an odd-fire engine with an even fire distributor in it either...
     
    w3srl, Nov 1, 2010
    #17
  18. sparky

    sparky Sandgroper Staff Member Founder

    True, but they don't run right. I know this by experience. ;)

    I know, I made assumptions there, like that it was running, and running well, and not transplanted from a marine application. I was just stating that the most reasonable explanation was that it's an odd-fire V6. Now, if it didn't run well, or there was some other issue, I'd encourage digging further, but on the face of it, 99.9% of the time, I'm correct. I was just trying to give the simplest, quickest, easiest way to tell with the information that was given.
     
    sparky, Nov 1, 2010
    #18