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Thread: Head bolts over stretched from using ARP thread lube instead of oil?

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    Head bolts over stretched from using ARP thread lube instead of oil?

    Hey Guys,

    Just installed the replacement ZD30DI cylinder head over the weekend, followed the Nissan workshop manual to a tee.
    But with one exception being, i used ARP ultra torque lube on the new OEM head bolts rather than just engine oil.

    On a couple of the bolts on the last 90 degree pass there was a section where it felt like the bolt lost tension or got "easier" to turn, but then got harder again towards the end of the pass.

    What i am trying to work out is whether ARP lube will give incorrect torque wrench readings compared to engine oil? & have i possibly over torqued the head bolts causing them to stretch past their yield point? (meaning there stuffed & need to be replaced)

    Also if i do end up needing to replace the head bolts, is it possible to reuse the head gasket or will this need to be replaced?


    Have done a bit of research into it & getting some conflicting info:

    "Nonetheless, should the yield point of a bolt be exceeded, the technician will feel a pronounced “softening” of the load, almost as if the threads have been stripped off the bolt. At this point, the bolt is over stretched (if it does not break first) and most, if not all of the clamping force supplied by that bolt is lost - (https://www.mechanic.com.au/news/tig...the-right-way1)


    "Unlike ordinary head bolts, TTY head bolts are designed to deform – but do it in a controlled way. Like a standard head bolt, a TTY bolt will stretch and spring back up to its yield point. But once the yield point is passed, the bolt becomes permanently stretched and does not return to its original length. Because of this, TTY bolts should not be reused." - (https://www.enginebuildermag.com/200...head-bolt-use/)


    Any help is much appreciated guys!

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    Patrol God mudnut's Avatar
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    For what its worth, the mechanic that reconditioned my engine scoffed at buying new head bolts. But I have always bought new bolts.
    Last edited by mudnut; 23rd November 2020 at 03:57 PM.

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    I used brand new OEM bolts & cleaned/chase the threads/holes in the block. So don't think it was anything to do with that

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    I just read the lab results from ARP for their bolt lube product and its designed to provided, and was proven to provide a tighter 'scatter' of torque and un-torque results than oil and a couple of others, so on balance it looks like you have used the premium bolt lube to deliver a consistent torque to the bolt. I wonder about the variability of the bolts themselves? What you won't know is the manufacturing and strength tolerance of the nissan Bolts unless they tell you the 'standard' they are made to. there are numerous different standards for bolt strength, - a gr 8.8 bolt supplied under one standard may actually have different properties than another bolt 8.8 under a different standard ( material variability, hardening, normalising, stress relieving etc). I guess I am saying, the yield point you appear to have reached may be across the tolerance range for that grade of bolt and standard. I don't think there is a problem with the lube - if anything you have increased your chances of a closer result using it. It would be a fair assumption that Nissan does not get all their bolts from one manufacturer also, and there in lies another tolerance issue.

    Torqueing them beyond their yield point does not mean they are stuffed necessarily. Below yield they will remain stressed with the ability to 'rebound with 'plasticity'. Once yield is reached the grain structure is irreversibly changed, ie stretched', and the bolt cannot return to its original dimensions as its likely thinned locally as well( minutely). The bolt still has load holding capacity for a short period beyond yield being exceeded then typically drops off - any bolt curve will demonstrate this - its more a matter of how far past yield you have gone. Without sophisticated tensiometers, and sensitive lab gear you won't know.

    Its hard to give you a definitive answer unfortunately. i guess the question is how far/rotation wise in the final 90 deg segment did you continue torqueing until you reached you intended torque value. If it was a further 80 deg, i would replace the bolt, if its 5 deg, i would say leave, maybe up to 10 deg - just my 'subjective' values.

    Regards reuse of the head gasket, i think most are designed to only be torqued down once as they crush to meet the specific local load. if you re-use you may not get the repeated crush identical to previous, and the seal would be compromised.

    I think a call to an engine building workshop might give you a better feel for where you are as well.

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