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Thread: Rod Bolt Stretch

  1. #1
    Junior Member Grease Monkey
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    Default Rod Bolt Stretch

    Hi guys,

    Does anyone know what 7AFE rod-bolts are to be stretched to? I don't want to use a torque-wrench, i want to do it the right way, so please dont argue about it haha

    I have a fairly basic 7AFE torque guide but it doesn't have the info i'm after

    Cheers

  2. #2
    Junior Member Automotive Encyclopaedia
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    Default Re: Rod Bolt Stretch

    All bolts have to be torqued up to a certain point, even if angle torqued from there on ...

    Checking for stretch on a bolt is only done if re-using the bolt & is done by measurung the bolt length when removed ..

  3. #3
    Junior Member Grease Monkey
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    Default Re: Rod Bolt Stretch

    No not exactly man, a rod-stretch gauge is used when you want to do the rod-bolts up perfectly, a torque gauge doesn't do this (too many factors to take into account), hence why ARP recommend stretching their rod-bolts.

    So yeah, not here to argue please, just want to know what they're to be stretched to

  4. #4
    As dodgy as a Backyard Mechanic GT1978's Avatar
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    Default Re: Rod Bolt Stretch

    Are you replacing the bolts with ARP ones? or putting in the stock bolts? If they are ARP bolts I'm sure the stretch could easily be gotten from there website or even through an email to them. If they are toyota I don't know if the info would even be available?

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  5. #5
    Backyard Fabricator Automotive Encyclopaedia
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    Default Re: Rod Bolt Stretch

    Toyota doesn't speficy a stretch length in the 7A manual, if they're ARP bolts then I'd check with ARP what stretch length they recommend. The rod-bolt info from the 7A manual is here:



  6. #6
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    Default Re: Rod Bolt Stretch

    No unfortunately, not ARP

    And as far as i can tell, noone "seems to care" at toyota, just torque them and hope that'll do

    Thanks anyway guys

  7. #7
    Junior Member Too Much Toyota
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    Default Re: Rod Bolt Stretch

    ... 'cause Toyota are happy with the torque-to-yield approach that they use for one-time bolts like main caps and head bolts. Even the diesels work this way and head torque is much more critical for them (not to mention much, much, fucking higher).

    The above mentioned process is more than just do the bolts up to the torque specs - the 90 degree turn (or 2 turns for other engines) put a specific amount of strain on the bolts making them more efficient at their job than simply doing up to a set torque.

    It also allows them to not worry about the length of bolts and focus more on the metalurgy/composition of the bolts so that when they're done to their specs the clamping force is more than adequate for the use of the bolt.
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  8. #8
    Junior Member Automotive Encyclopaedia
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    Default Re: Rod Bolt Stretch

    Quote Originally Posted by 70XIN View Post

    And as far as i can tell, noone "seems to care" at toyota, just torque them and hope that'll do
    It comes down to how many bolts have failed & or come loose this way to date on standard motors & i think that will give you the answer as to why no one seems to care about doing it any other way at Toyota .........

    And as has been previously mentioned unless you are using ARP bolts the stretch to yield that you talk about would be inaccurate due to different metallurgy, you could be actually over stressing the standard bolts ..

  9. #9
    Junior Member Grease Monkey
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    Default Re: Rod Bolt Stretch

    It's the weak link of the motor, plenty of rod-bolts have unwound or failed in 7A's.

    Yep, i guess i'll just do it the toyota way

  10. #10
    Bull now in china shop! Domestic Engineer NME308's Avatar
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    Default Re: Rod Bolt Stretch

    Quote Originally Posted by 70XIN View Post
    Does anyone know what 7AFE rod-bolts are to be stretched to? I don't want to use a torque-wrench, i want to do it the right way, so please dont argue about it haha
    ----------------------------------------------------------------------------------------------------------------------------------
    So yeah, not here to argue please, just want to know what they're to be stretched to
    ---------------------------------------------------------------------------------------------------------------------------------
    No unfortunately, not ARP

    And as far as i can tell, noone "seems to care" at toyota, just torque them and hope that'll do
    ----------------------------------------------------------------------------------------------------------------------------------
    It's the weak link of the motor, plenty of rod-bolts have unwound or failed in 7A's.
    You arn't making much sense mate!
    If you are aware of rod bolt issues with the toyota items, why on earth wouldn't you be putting in the best bolts money can buy while you have it all apart?? Assuming you have it apart by choice not just looking at a conrod through the block!

    Cheers,
    Jason
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  11. #11
    Junior Member Grease Monkey
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    Default Re: Rod Bolt Stretch

    The person i'm building it for is on a VERY strict budget.

    Unfortunately, he can't shell out $550 for forged rods, and it'll cost close to $300 to supply, drill/tap the rods for ARP bolts (nothing off-the-shelf is anywhere near the same spec), and resize the bigends.

    So yeah, from what i've been told by many, the *only* real way to do up rod bolts is with a stretch gauge. So yeah ... i just wanted to do the bolts up the right way and hope that new bolts/resized bigends will survive.

  12. #12
    Junior Member Too Much Toyota
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    Default Re: Rod Bolt Stretch

    follow the manual and treat the bolts as a one-use item - once they've been torque'd-to-yield (as per the TSRM above) a second attempt to do that will stretch them too much and they will fail prematurely

    Simply doing them up to XX ft/lb will also be a fail.
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  13. #13
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    Default Re: Rod Bolt Stretch

    Yep, shall do

    Cheers guys

  14. #14
    Bull now in china shop! Domestic Engineer NME308's Avatar
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    Default Re: Rod Bolt Stretch

    Strict budget?
    You should of said so!!!

    I understand strict budget mate!

    Good luck!
    3TC Compound Turbo 1976 TA23 - Members Ride Thread HERE
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