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Thread: Big block engine mount issue

  1. #1
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    Big block engine mount issue

    Not a Donzi question, but a big block Merc question...

    It appears the starboard 454 (inboard with hurth transmission) in my 91 Searay express is moving. I'm looking at the saddle mounts for sagging, but there is evidence of shifting and sliding on the pins of the mounts themselves. Does anyone have the torque specs for the mounts, I found specs for the mounts to the block, but need specs for the rest. There are 4 mounts bolted to the block, each mount slides in and out of a second bracket that is clamped by a nut and bolt, this second bracket is held to the stringers with 1-1/16" nuts.

    I have the mount to block specs, but require the torque specs for the nut and bolt , and the torque specs for the big nuts.

    Any help would be appreciated.

  2. #2
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    Big block engine mount issue

    This is the universal standard for bolt torque when a spec is not available.
    BOLT TORQUE SPECIFICATIONS, Unified Standard -- UT-120

    When the Workshop Manual does not give a torque specification for a fastener, use the standard torque numbers in the following table. Unless otherwise specified, all threaded fasteners in the MGA will be equal to Unified Grade 5. There should be no Grade 2 fasteners anywhere in the car. Most of the torque specifications given in the Workshop Manual will be higher than Grade 5 in this table, because those fasteners are (originally) better than Grade 5.

    BOLT TORQUE SPECIFICATIONS - For Unified Standard Threads
    Torque in pounds-foot
    Fastener
    Grade >>>
    2 5 7 8 Socket head
    cap screw
    Bolt
    Dia.
    Threads
    per inch
    Dry Oiled Dry Oiled Dry Oiled Dry Oiled Dry Oiled
    1/4 20 4 3 8 6 10 8 12 9 14 11
    1/4 28 6 4 10 7 12 9 14 10 16 13
    5/16 18 9 7 17 13 21 16 25 18 29 23
    5/16 24 12 9 19 14 24 18 29 20 33 26
    3/8 16 16 12 30 23 40 30 45 35 49 39
    3/8 24 22 16 35 25 45 35 50 40 54 44
    7/16 14 24 17 50 35 60 45 70 55 76 61
    7/16 20 34 26 55 40 70 50 80 60 85 68
    1/2 13 38 31 75 55 95 70 110 80 113 90
    1/2 20 52 42 90 65 100 80 120 90 126 100
    9/16 12 52 42 110 80 135 100 150 110 163 130
    9/16 18 71 57 120 90 150 110 170 130 181 144
    5/8 11 98 78 150 110 190 140 220 170 230 184
    5/8 18 115 >93 180 130 210 160 240 180 255 204
    3/4 10 157 121 260 200 320 240 380 280 400 320
    3/4 16 180 133 300 220 360 280 420 320 440 350
    7/8 9 210 160 430 320 520 400 600 460 640 510
    7/8 14 230 177 470 360 580 440 660 500 700 560
    1 8 320 240 640 480 800 600 900 680 980 780
    1 12 350 265 710 530 860 666 990 740 1060 845

    Baseline torque is calculated for a non-lubricated, un-plated bolt.

    BOLT TORQUE FACTORS
    LUBRICANT OR PLATING TORQUE CHANGES
    Oil Reduce torque 15% to 25%
    Dry Film (Teflon or moly based) Reduce torque 50%
    Dry Wax (Cetyl alcohol) Reduce torque 50%
    Chrome plating No change
    Cadmium plating Reduce torque 25%
    Zinc plating Reduce torque 15%

    Hope this helps,
    Sid

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