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grade 8 good enough for the motor mount bracket...........

Discussion in 'The Garage' started by down4thakrown, Jun 8, 2005.

  1. down4thakrown

    down4thakrown 1/2 ton status Premium Member GMOTM Winner

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    that bolts to the sid of the block with the 3 bolts?
     
  2. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    More than enough.
     
  3. mechted

    mechted 1 ton status Premium Member

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    we had this same question about an engineering project we just finished for school... so i went looking for bolt specs and found this...
    http://www.rockcrawler.com/techreports/fasteners/index.asp
    strength in tension and shear for common bolt sizes... should answer any question about "is this bolt strong enough" for you
     
  4. Hossbaby50

    Hossbaby50 3/4 ton status

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    It doesn't really get better then grade 8 unless you are talking about expensive aircraft bolts or specialty bolts that are expensive also.

    Harley
     
  5. 79k20350

    79k20350 3/4 ton status

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    I just put in a motor, grade 5 is what came stock on my 350 although i had some grade 8 lying around so i used those just because the heads on the grade 5 ones were bad. if you have grade 8 bolts your fine, but really from the factory grade 5 was all they needed.
     
  6. k5freak44

    k5freak44 1/2 ton status

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    i have heard that grade 8 is the strongest but can break a little easyer then grade 5 from being too rigid.

    is this true?
     
  7. redneckdude

    redneckdude 1/2 ton status

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    Ive heard something similar. Grade 5 will bend before it brakes, grade 8 has no give/bend so it just breaks. It takes more for a grade 8 to break than it does 5 tho AFAIK.
     
  8. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    That's what I was gonna say, more than enough with grade 8
     
  9. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    G8 is stronger than G5 in every way. G5 will fail completely in both shear and tensile stress before G8 will even deform. The "old wives tail" about G5 being "better because it will bend" is simply not correct, but possibly due to the fact that G8 often does not show signs of stress before failing where you can often see bent or deformed G5s before breaking. But the simple fact is that if you break a G8, the G5 would have been LONG gone...
     
  10. Hossbaby50

    Hossbaby50 3/4 ton status

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    I personally have bent Grade 8 bolts and seen other people bend them also. Like Baddog mentioned. They take alot more load without breaking but when they break they do tend to shear off or snap.

    Grade 5's usually bend/deform more before they break but Grade 8's will bend/deform also depending on the circumstance. They just don't bend/deform as far before they break off.

    Harley
     
  11. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    lol, i wonder how long that "gr 5 is better" myth is going to survive. Seems never ending... every time i see someone say that on a forum i correct them, but new people keep on bringing it up. Maybe there should be a pasty about this in the garage forum... lol! :grin:

    j
     
  12. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I was wondering that myself.
     
  13. k5freak44

    k5freak44 1/2 ton status

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    :blush: lol i shouldent have said anthing :cool1:

    the only reason i said this, is becasue the last time i made a similar post to this one someone told me grade 5 was better.
     
  14. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    actually, it was a good thing that you did... the last thing we need is some poor noobie guy ending up dead because he "heard" that gr 5 was better and so he used it on all his suspension and steering parts. If you're not an engineer and can't run the numbers on a fastener, its a pretty good rule to always use gr 8 for auto applications if its going to be subjected to much load at all. Sometimes it will be overkill... but overkill in this case isn't going to get you killed like under-spec'ing something might. :)

    j
     

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