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Thread: Head bolt "situation"...

  1. #1
    Registered User Pilgrim's Avatar
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    Default Head bolt "situation"...

    I was just re-installing the head on my 1983 280ZX Turbo when I ran into two problems:

    1) One bolt would not tighten properly. It was one of the last I installed, and when I turned it and got no increase in resistance past about 30 lbs/ft, I decided that I probably had a bad bolt. At least I was smart enough NOT to keep turning it, which would most likely have broken it off. I checked the bolt hole to confirm that there wasn't debris in the bottom blocking the end of the bolt, then re-used one of the original bolts and it torqued down just fine so the head is torqued into position properly. I have a new bolt ordered.

    2) Of more concern - I had all the head bolts but the one above installed and realized I had not put the washers from the original bolts under the heads of the new ones. I removed the new bolts one at a time and installed the washers, re-torquing each bolt as I re-installed it.

    But - these are supposed to be one-time use bolts. I don't want to blow a head gasket, but I also am not fond of the idea of paying another $100 for a replacement head bolt set. The bolts were torqued and sat for about an hour before I realized the washers were missing.

    I have some options...

    - Replace the individual bolt, torque it, go on with life.
    - Replace the individual bolt, then make one more round of the head bolts adding 3-5 lbs/ft of torque to stretch the bolts slightly.
    - Replace the entire head bolt set.

    Your thoughts, please?
    Last edited by Pilgrim; 08-02-2014 at 05:47 PM.

  2. #2
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    Default

    I'd go with option 1 and re-torque all of them after a few hot cold cycles & then decide what the next step is based on what I found.

  3. #3
    HLS30A 17574 djwarner's Avatar
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    The design intent of one time use bolts is to stress the bolt to a point beyond its elastic limit. This causes the bolt to deform (read lengthen). This leaves a residual tension near the point of yield. As the engine thermal cycles, some additional creep may occur.

    As the bolt yields, the crystalline structures inside the bolt grow. Repeated torqueing to the point of yield causes the crystals to grow more. The weakest part of the steel is the boundary between crystalline and non-crystalline elements. As the grains grow in size, a bolt becomes weaker and more likely to fail catastrophically.

    So you may be able to re-torque the bolts up to the specified limit for a second time. They may fail as you torque them down, after a heat cycle or two, or the next time you try to remove them. Point is that it is a shot in the dark. And the question is the expense in time and labor to pull the head and removing broken bolt shanks versus the cost of new bolts now while the head is off. The professional engineers say replace them now.
    1971 240Z HLS30A 17574 L24-021025

  4. #4
    Registered User LeonV's Avatar
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    I agree with Mark, I'd go with option 1. Just put in the missing bolt and torque it down.

    These are not torque-to-yield bolts, I'm curious where you got that bit of info?
    2/74 260Z

  5. #5
    Supporting Member Diseazd's Avatar
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    I'm with Mark and Leon........go with option 1.
    http://www.flickr.com/photos/1404980...7600346077563/
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    70, 71, 2 72's, and a 73 240z....
    90 300zx and a 1996 Acura NSX.....but who's counting?

  6. #6
    Registered User siteunseen's Avatar
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    I used ARP turbo bolts when I rebuilt my '77. After 500 miles I re torqued them as their directions recommend. From the ARP wb site, " Because the head gasket will compress upon initial torquing, make sure studs (or bolts) are re-torqued after the engine has been run."
    The Official ARP Web Site | Manufacturing
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

  7. #7
    Registered User Pilgrim's Avatar
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    I went with option #1 - pulled all bolts one at a time, installed the missing washers, and when the replacement bolt arrived, removed it, installed the new bolt with washer.

    And...last weekend while I was trying to get the cam sprocket on, I realized the timing chain tensioner had dropped and I'm going to have to pull the front end cover and crank pulley to get the tensioner back in place. That's another thread...

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