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Thread: 2bolt to 4 bolt conversion

  1. #1
    Senior Member
    Join Date
    Apr 2010
    Posts
    6,425
    what are your thoughts on this? i know the castings are the same and all you have to do is put the 2 extra holes in for the bolts but can a machinist line bore the 4 bolt cap on the 2 bolt block accuratly?i would imagine it would cut into the block and maybe end up with a spun bearing. not sure if im making sence, is it better to use an after market cap so you can use the splayed setup? thanks

  2. #2
    Fiat48
    Done correctly a 4 bolt conversion is fine. The key is "done correctly." I would say to do this only if you know a machinest who has done many of these before. The straightness and sizing of the main bores is highly critical. Splayed caps would be the way to go, but I am not sure this can be done without getting into the oil galley.

  3. #3
    Hotcrusader76
    I almost considered having Ed Hale Machine Shop perform this upgrade to my 2-bolt as well. But considering it's "Lake Boat" status and my budget I choose not to.
    After 2-weeks of calling around and e-mailing people I found that this modification is worth it's money. But this info is only as crediable as the builders I got it from since I have had no experience as of yet using this in a motor.

  4. #4
    OMEGA_BUBBLE_JET
    Just a thought......there are far more 2 bolt blocks running up and down the tracks than 4 bolts. When was the last time you heard someone breaking a main cap due to failure??? If it ain't broke don't fix it. I don't buy into the whole 4 bolt thing. I have seen engines making well over 700 hp on 2 bolt blocks.
    Omega

  5. #5
    Ronnie
    The shop that does all of my motors does this conversion all the time for drag motors. As you know 4 bolt blocks are getting hard to find and very costly. The main thing is to start with a set of caps that line up very close before you start. Then after you line them up line bore the block. this is a cost effective way of getting a 4 bolt block.
    Ronnie

  6. #6
    LeE ss13
    OMEGA_BUBBLE_JET:
    Just a thought......there are far more 2 bolt blocks running up and down the tracks than 4 bolts. When was the last time you heard someone breaking a main cap due to failure??? If it ain't broke don't fix it. I don't buy into the whole 4 bolt thing. I have seen engines making well over 700 hp on 2 bolt blocks.
    Omega Amen to that !!!
    [ June 05, 2003, 08:26 AM: Message edited by: LeE ss13 ]

  7. #7
    GofastRacer
    I run 2 bolt caps on mine and I turn 7500 with it. Lose the bolts and use studs though!.

  8. #8
    Senior Member
    Join Date
    Apr 2010
    Posts
    6,425
    i was just worried that when they line bore it to match the caps to the block too much material may be taken off the block side of the mains bore possibly ending up with a spun bearing.

  9. #9
    GofastRacer
    Fiat48:
    Done correctly a 4 bolt conversion is fine. The key is "done correctly." I would say to do this only if you know a machinest who has done many of these before. The straightness and sizing of the main bores is highly critical. Splayed caps would be the way to go, but I am not sure this can be done without getting into the oil galley. I've converted quite a few 2 bolts over to 4 bolts but I think that the main webs become weaker due to the material being taken out for the bolt. Only benefit I see maybe a bigger cap to prevent the cap walk. Splayed caps are the way to go and they do work in big blocks very well!..

  10. #10
    Fiat48
    OMEGA_BUBBLE_JET:
    Just a thought......there are far more 2 bolt blocks running up and down the tracks than 4 bolts. When was the last time you heard someone breaking a main cap due to failure??? If it ain't broke don't fix it. I don't buy into the whole 4 bolt thing. I have seen engines making well over 700 hp on 2 bolt blocks.
    Omega I agree with you on the breaking the main cap. Relatively unheard of. And 4 bolts (unless splayed) don't keep the caps from walking around in high horsepower applications either. But here's the catch. If you put a lot of money on a 2 bolt motor and decide to sell it, most people will just pass as they want a 4 bolt motor. So here lately I have been inclined to build the aftermarket blocks (although 2 of them have been line honed incorectly brand new) as they are stronger and bring the money back if you decide to sell.

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