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4 bolt main ?'s

Discussion in 'The Garage' started by unicknn, Jan 16, 2003.

  1. unicknn

    unicknn 1/2 ton status

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    4 bolt main ?\'s

    What exactly does 4 bolt main mean? What other kinds of mains are there and what are the advantages and disadvantages of them?

    lmk
    Nick
     
  2. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Re: 4 bolt main ?\'s

    "4 bolt main" refers to the main bearing caps of the engine having four bolts that hold them in place, as opposed to two as most production engines have. A "4 bolt main" engine block is normally a performance block that can handle more torque/rpm than a standard block.

    John
     
  3. Shaggy

    Shaggy 3/4 ton status

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    Re: 4 bolt main ?\'s

    <font color="green"> A 4 bolt main means that each main cap (the bearing caps that hold the crank in) have 4 bolts, 2 on each side. There are 3 main caps that would have the 4 bolts, and a total of 5 caps, but the end ones usually have 2 bolts in any application, IIRC. THe other variation is a 2 bolt main. In general, a 4 bolt main is a bit stronger and should be used in very high horse power engines. In reality a 2 bolt main is usually fine for anything under 350-400hp, but if you have a choice between a 2 or 4 always go for the 4.

    Another variation is called splayed caps, these have 4 bolts and the outer bolts are splayed out for even more strength. Here's a shot of a 454 with splayed caps -

    [​IMG] </font color>
     
  4. unicknn

    unicknn 1/2 ton status

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    Re: 4 bolt main ?\'s

    cool thanx for the info
     
  5. balzackks84

    balzackks84 1/2 ton status GMOTM Winner

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    Re: 4 bolt main ?\'s

    Something that ive heard from someone that bulds engines is that the 4 bolt is only stronger after 5500 rpm, up to that point the 2 is just as strong. There is also a product that you can somehow make the 2 bolt a 4 bolt with tabs and taping the block. Im not too sure on this one tho, ive just heard about it. But supposedly this method is stronger than a stock 4 bolt main (read: excluding above photo)
     
  6. outlaw612

    outlaw612 1/2 ton status

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    Re: 4 bolt main ?\'s

    youre talking about splayed mains. Look at Shaggy post above. You can use a 2 bolt main block and buy aftermarket caps(I believe Miloden makes some) to convert it to splayed.
     
  7. Shaggy

    Shaggy 3/4 ton status

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    Re: 4 bolt main ?\'s

    <font color="green"> Outlaw is right, the splayed mains are used on adapted 2 bolt blocks. Willyswanter is the one that modified the block in the above picture, the motor is going to be a 650+ HP 496 that's going into his 53 Willys. </font color>
     
  8. balzackks84

    balzackks84 1/2 ton status GMOTM Winner

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    Re: 4 bolt main ?\'s

    Ok. I've never actually seen them before. Thanks for clarifying.
     
  9. bablazer73

    bablazer73 1/2 ton status

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    Re: 4 bolt main ?\'s

    If you are running a 2 bolt block and are worried about the caps flexing, There are company's that make cap "straps". these are basically heavy pieces of steel straps that attach to the main bolts and reduce flex on 2 bolts. A kit is usually under 100.00 and can make a block stronger, inexpensivly.
     
  10. afroman006

    afroman006 1/2 ton status

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    Re: 4 bolt main ?\'s

    Shaggy, how much did it run you to get the holes drilled and tapped for the splayed bolts? And also where could I find some of those 2 bolt braces? Thx
     
  11. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    Re: 4 bolt main ?\'s

    First of all, thats my engine pictured, not shaggys. /forums/images/graemlins/thumb.gif Second, I drilled and tapped them myself. It's farely easy to do yourself using the caps as a guide to drill the holes. Just don't go too far and end up in an oil gallery. Took me about 2 hours to drill and tap them all including bottom tapping them and chamfering the holes. BUT, there is machine work required to make them work. You have to torque the caps on with the 2 innner bolts and measure the gap on the ends between the cap and block. The instructions give a range for this measurement. If it is off you have to machine the cap down to the right size. I had to machine them all using a normal mill. That took about an hour to do. So in all 3 hours of actual working time.

    Converting a 2 bolt main to a splayed 4 bolt is stronger than a stock 4 bolt because of the angled outer bolts plus the main webs in the block are stronger on a 2 bolt.

    You will have to have an align bore done on the mains after you do this however.
     

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