Re-torquing head bolts

Kdancy
Kdancy
in HUDSON
Do you-
Just go over each one in the correct pattern without loosening?
Loosen one at a time then torque to specs?
Loosen all, then do a 3-4 step torque as done at first?

Comments

  • 48rob
    48rob
    Kerry,

     I was taught to do as you describe in your second option;

    Loosen one at a time then torque to specs, but just loosen, as in just barely move it, then tighten.

    Rob
  • Frankvintagefullflowcom
    Frankvintagefullflowcom

    While we're at it, lets address the question of "lubricated vs un-lubricated" threads. Actual clamping force for a given torque value is vastly variable and different between the two. What say our experts?

    F

  • Frankvintagefullflowcom
    Frankvintagefullflowcom

    True, one must use one's head. Torque specs are sometimes given for both scenarios. The problem with dry specs are that they are dependent on factors unknown to the user, A lubricated spec somewhat levels the playing field.

    As an experiment, when I recently replaced the head gasket on our '47 six, I torqued to 40 lb (in about 6 passes), did a heat/cool cycle, torqued again and did another heat/cool cycle and re-torqued. I marked each stud/nut, then removed them, one at a time, lubricating them upon re-assembly. I reduced the wrench setting to 37.5 and retightened, also one at a time. With little variation, each went about 90 degrees past the marks at the reduced setting.

    Reading torsional resistance produced by friction isn't a very good indicator of clamping force.

    Just another of Frank's observations/opinions. There are more.

  • drivergo2
    drivergo2
    That's good to know!
  • Geoff
    Geoff
    Why loosen and re-torque at all?  If the head has been pulled down, I can't see the reason for doing this. 
  • Frankvintagefullflowcom
    Frankvintagefullflowcom

    Because it really isn't "pulled down"....at least not to the degree that the designers intended. The torque you are reading on the wrench reflects a significant amount of force just to overcome friction.....force that doesn't contribute to clamping force. After all, the whole idea of tightening the capscrews/bolts/nuts is to achieve some necessary degree of clamping of two (or more) components in an assembly.

    Frank 

  • Frankvintagefullflowcom
    Frankvintagefullflowcom

    Hmmmmm. It just occurred to me that I responded to something that Geoffrey didn't say. I'd "unpost" it if I knew how.

    My apologies. I was still on the Lube vs no-Lube theme in my head.

    F

  • GrimGreaser
    GrimGreaser
    edited July 2015
    Take from it what you will...
    www.arp-bolts.mobi/p/tech.php?page=3
This discussion has been closed.

Categories

In this Discussion