Main cap bolts

Discussion in 'Race 400/430/455' started by BQUICK, Feb 9, 2022.

  1. BQUICK

    BQUICK Gold Level Contributor

    Any advantage of 125-5201 ARP main cap bolts vs stock ones?
     
  2. sean Buick 76

    sean Buick 76 Buick Nut

    I’m sure they are a much better fastener however I would re hone or at least measure the main line. Better fasteners changes the clamping forces.
     
  3. hugger

    hugger Well-Known Member

    I've heard the stock bolts are actually a VERY good material,...from a few different builders,....Are they better than ARP,..probably not but certainly not something that eould keep me up at night
     
    Mart likes this.
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  5. standup 69

    standup 69 standup69

    The stock bolts are most likely stronger than what they are threaded into ..pick your fusible link ..
     
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  6. stage2man

    stage2man Well-Known Member

    I’ve wondered the same thing. At work when we do stress analysis on threads one thread shows red outside the plastic region of the stress strain curve. We have to do ratcheting to represent what really happens, spreads the load across thread faces as metal moves. If the tensile strength is to high then all this happens in the block. The other negative thing I worry about with studs is they place this stress field to deep under the mating surface. That said, I have studs
     
    482 likes this.
  7. 482

    482 Big Member

    I've put main studs in most all the BBB I've built with no problems. Would you suggest reducing the studs shank diameter to increase the 'bolt' stretch and redistribute the deep loading or machine out and reshape the 'red thread area' to reduce or redistribute the modeled over yield stress concentrator like a Wentworth thread? Don't know if you could re-roll the compromised area somehow and re-heat treat.
     
  8. stage2man

    stage2man Well-Known Member

    Yeah, I haven’t had any issues with my studs thru girdle. And I believe the factory coarse thread is best for cast iron. I’m no expert on the subject. But as far as factory bolts go, I’ve had no issues there either. I sprayed 300hp floggers on factory bolts with no block failures. But when looking at the thread boss area I’ve often wondered why place the stress here. 1x to 1.5 x the bolt diameter would likely hold fine without going below the thick mating face. This is likely what TA does with the four bolt mod. I see no reason to put displacement producing vibration into the webbing. Interesting subject anyway.
     
    sean Buick 76 likes this.
  9. Jim Weise

    Jim Weise EFI/DIS 482

    What I found over the years lines up with what David is saying. Studs load the block differently, and unfortunately, not always the same. Any deviation in torque, lubrication, or cleanliness can alter the housing size once the studs are torqued. Bolts tend to be much more forgiving.

    Buick factory main bolts are very good, I used to replace the bolts with ARP ones, but after consulting with my machinist at the time, who was a complete nut when it came to housing bore consistency, he agreed with me that the stock Buick bolts are very good pieces, and there is little to be gained by replacing them. The webbing of the block is the concern when it comes to breakage in this area, not the fastener.

    Now, I have done many girdled/water jacket filled blocks, and that housing bore consistency issue does not occur in those blocks. The girdle distributes the stud load, and the filler resists block distortion.

    And of course the proof is in the pudding.. I currently have about 60 factory iron block 455 based motors, that produced between 550 and 700 HP in service around the world.. and not one main bearing failure has been reported back to me.

    JW
     
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  10. gsjohnny1

    gsjohnny1 Well-Known Member

    stage2man;
    ''displacement producing vibration into the webbing'' interesting item. i know the way the block is cast and all its irregularities leaves a lot to think about on how/why the material changes its value due to changing conditions we put it thru and how can we correct it or make it last longer. the bolts never gave me any indication on being cheap. i do use arp head bolts only because of running a blower
    back to the drawing board now.
     
  11. sean Buick 76

    sean Buick 76 Buick Nut

    When Bill M completed his dyno and track testing he found the caps mains were moving forward and backwards causing bearing issues. That was using an eagle billet crank. With a factory crank the issue must be much worse. He looked into cross bolted mains with custom caps and decided the solution was the 7/8” thick girdle we designed and made.
     
  12. Bens99gtp

    Bens99gtp Well-Known Member

    I'm no professional builder, but how well a main cap fits into the block is something I feel gets overlooked very easy. I lost a motor that had good main studs right from AMP. Got 3 1/8 mile passes b4 I noticed a 7 psi oil drop at idle....the mains were shot on 2,3,4. 1 and 5 and all the rods looked as good as could be with all the stuff in the oil, crank wasn't bent or cracked. But noticed on tesr down with the studs out the caps didn't require any force to remove or install into the block.

    I wonder how much of this cap walk do we blame on bolts and studs where the issue is cap or block
     
  13. sean Buick 76

    sean Buick 76 Buick Nut

    Flexy crankshafts and flexy main bolts help keep the flexy block from failing. Add bandaids and prolong the inevitable. Most just run it and hope for the best, the bandaids are hit and miss.
     
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  14. gsjohnny1

    gsjohnny1 Well-Known Member

    cast iron vs steel are 2 totally different venues that react differently under force/pressure. your right about 'bandaids'.
    but they not totally the correct answer to solve the issues.
    if main caps were made like some connecting rods that have a counterbore and shoulder to lock together like the lentz rods
    i use, that would be a definite upgrade in keeping the mains caps located. then again how much do we want to spend.
     
  15. 482

    482 Big Member

    Keith Black type top fuel Nitro motors (blocks) are made to let them twist and move under the huge torque instead of bust. Street / Strip engines are designed to be ridged and not move around, like sealing cylinder bores to rings and keeping bearings in place with girdles etc. Both use cranks from 4340 Chrome Moly steel, both can use Aluminum cased blocks. Apples to Oranges I know but at what horsepower do you start designing for a bit of flex and movement and less from rock solid rigidity? Depends on compromise I guess like Pro stocks steel or Aluminum con rods use?
     
  16. Schurkey

    Schurkey Silver Level contributor

    ARP brags-up that they roll the threads AFTER heat-treating the steel.

    GM main bolts are described in the Standard Catalog as "Grade 8" and "300M"

    https://www.techsteel.net/alloy/steel/300m
    But no mention of thread-rolling before or after heat-treat.
     
  17. Tom Righter

    Tom Righter Well-Known Member

    If those main bearings were fried the loose caps are likely the cause of the heat that went into the caps as they cool they shrink and no longer fit in the register tight. However you are correct that the tighter the fit the better
     
  18. Mart

    Mart Gold level member

    I would call it distortion.
     
  19. Tom Righter

    Tom Righter Well-Known Member

    Agreed the key to repeatability when using studs following the same torque procedures each time. Also cycling them several times, and never tighten stud in the block. Leaving it loose allowing it to find its happy place. Following these procedures using studs Would be an upgrade and cause less stress on the block versus a bolt.
     
    sean Buick 76 likes this.
  20. Mart

    Mart Gold level member

    I wonder what GH or possibly GL GM used on the specs for the block tapping?

    GH meaning in taps.
    GH is short for “Ground High”. “3” is number of 0.0005 increments applied over “basic” tap pitch diameter defined by the Class-of-Fit assigned. Pitch-diameter adjustments fine-tune the fit with the mating part. Occasionally, you may see GL instead of GH. GL means “Ground Low”.
     

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