Author Topic: 350 Engine Bolt Markings  (Read 1970 times)

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Offline slawsonb

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350 Engine Bolt Markings
« on: October 22, 2015, 05:16:19 PM »
I just disassembled my fourth 350 engine and am curious about the significance of the markings on the engine bolts (the 17 that hold the cases together). I have seen 6, 6T, 7, and 7T on the heads. My earliest engine (01351) had only 6 and 6T. The latest (07875) is the only one of these I have seen a 7T on. The other two (in the 035xx range) had a mixture of 6, 6T, and 7. Does anyone know what these markings are intended to signify? The bolt sizes are all 6 and 8mm. It's a quandary.  ;D
...bert
« Last Edit: October 22, 2015, 10:31:13 PM by slawsonb »

Offline Sye

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Re: 350 Engine Bolt Markings
« Reply #1 on: October 23, 2015, 05:28:18 AM »
It signifies the grade of steel the bolt is made from and its tensile strength.

Grade 6 is now obsolete but grade 7 is as follows:

Medium-carbon alloy steel, quenched and tempered.
Minimum tensile strength in thousands of pound-force per square inch = 133.
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Offline slawsonb

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Re: 350 Engine Bolt Markings
« Reply #2 on: October 23, 2015, 11:07:30 AM »
Thanks Sye. Any idea about the "T"? I guess I'm used to more contemporary markings (tic marks on the head). Was this a Japanese marking technique? Used in the 60's and 70's?
...bert

Offline BRT-GTR

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Re: 350 Engine Bolt Markings
« Reply #3 on: October 24, 2015, 09:38:05 AM »
              Aaaaarrrrrrrrrrrrrggggghhhhhh!!!!.     'Step away from the bolt/screw minefield',  Bert. lol.

    The more research you do , the more confused you will get.  :D ;D :D

   I did find this, 'The markings such as 7T (other common ones are 4T and 9T) are Japanese Industrial Standard (JIS) grades and indicate 1/10 of the nominal tensile strength in kgf/mm2'.  
    I've seen references to the 'T' meaning max torque but it's more likely to refer to max Tensile strength as Sye states and I guess was used up to the adoption of ISO heads and thread forms around 1971. .
         Brian.
« Last Edit: October 24, 2015, 09:44:38 AM by BRT-GTR »
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Offline slawsonb

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Re: 350 Engine Bolt Markings
« Reply #4 on: October 24, 2015, 12:42:12 PM »
But Brian, you know I love a good minefield. ;D
Thanks...itch scratched.
...bert

Offline BRT-GTR

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Re: 350 Engine Bolt Markings
« Reply #5 on: October 24, 2015, 01:26:16 PM »
         Kaboooooooooooom !!, damn, found one.    ;D ::)            Brian
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