History repeats itself. The turbo car is broken again and will be for a while..

Discussion in 'Small Block Tech' started by jay3000, Apr 24, 2011.

  1. jay3000

    jay3000 RIP 1-16-21

    I'm not looking to re-design this thing personally.. I'm looking to fix what I have, or at least fix it so no one else can..

    I have ordered some 3/8 socket head cap screws that as strong as anything I can find and are designed to hold stuff DOWN and not for shear strength like a countersunk screw.. At least that's what I can find.
    The head is 9/16 wide and will be countersunk 3/16 the remaining part of the head above the bar will be clearanced for the rockers to fit.. This is WAAAAAAAAAAAAAAAAAAAAAAAAAAY stronger than what was in there.. Just need to find someone to do it now..

    If it continues to break the heads will get an AR-15 firing squad:blast:
     
  2. FJM568

    FJM568 Well-Known Member

    Just make sure when it goes back together that you line up everything straight. One of the things that the original flat head cap screws did for the setup was that it located the mounting plate parallel to the valves. Depending on the through hole size that is in the plate will determine the alignment of the plate. Normally, when drilling a hole for a threaded bolt, standard practices will be to drill 1/32 to 1/16 oversize for clearance. In this case, where plate alignment would be critical, personally, I would drill it to the actual screw size or no more than about .010 oversized(e.g. for a 3/8 cap screw, drill .375 - .385,in this case, use either 3/8 or V drill(.377), but no bigger than W drill(.386)).

    The tapered countersink is what located the plate originally, not the through hole. Chances are that when Mark drilled it originally for the 5/16 flat head cs, that he drilled the through hole to 3/8 already.
     
  3. jay3000

    jay3000 RIP 1-16-21

    This should be drilled so the threads are a tight fit and the square countersink is a tool for proper line up as well..
     
  4. bammax

    bammax Well-Known Member

    I'd just start all the bolts and then torque them down in a dancing pattern like lug nuts on wheels. Maybe even do it in increments. That should help ensure proper alignment and even load spreading across the length of the plate.
     
  5. FJM568

    FJM568 Well-Known Member

    True. Be aware that standard practice is to also make the cap screw head counterbore oversized as well. Most shops have a special cutter with a pilot to do that. So the machinist that you will have do this operation will need to be made aware that your tolerances will be much closer.
     

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