High Strength Bolts - Headmarks - NCRS Discussion Boards

High Strength Bolts - Headmarks

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  • Joe C.
    Expired
    • August 31, 1999
    • 4598

    High Strength Bolts - Headmarks

    Here is what I found when I removed all 10 main bearing cap bolts from my L76 engine.

    3 bolts: "N" inside single circle.
    2 bolts: "TR" inside single circle
    3 bolts: "TR" within 4 radial lines set at 0, 90, 180, 270 degrees
    3 bolts: "M" with 4 radial lines set at 0, 90, 180, 270 degrees.
    1 bolt: "TR" with 4 radial lines set at 0, 90, 180, 270 degrees.

    I have bought 5 new bolts from GM, which are marked with "O" with 4 radial lines set at 0,90, 180, 270 degrees.
    I have bought 5 new "stud/bolt fasteners", which are marked as pictured. These are to install a missing windage tray.

    I have looked at numerous SAE, and ASTM publications, but cannot find any correlation to neither a single circle nor a "4 lines" headmark. I assume that these fasteners are at least Grade 8. Does anyone have any further info.

    I understand that common grade 5 bolts have 3 radial lines @ 0, 120, 240*
    Grade 8 have marks @ 0, 60, 120, 180, 240, 300*.

    Thanks in advance.

    Joe




  • Joe C.
    Expired
    • August 31, 1999
    • 4598

    #2
    SUFFIX

    Make that 1 bolt: "M" ..........

    Comment

    • Duke W.
      Beyond Control Poster
      • January 1, 1993
      • 15610

      #3
      Re: High Strength Bolts - Headmarks

      SAE grades are number of radial lines plus two, so they are grade 6. Grades 3, 5, and 8 are the common commmercially available replacements.

      Not sure what the circle means, but given the size of these bolts and the torque spec, grade six is perfectly adequate.

      Duke

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