Anti-seize and over torquing bolts

Discussion in '80-Series Tech' started by CruiseOrlando, Jul 13, 2012.

  1. CruiseOrlando

    CruiseOrlando Conveniently Enhanced SILVER Star

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    Interesting article on Rock Auto's "My Garage" section of their newsletter concerning the use of anti-seize and torque settings. It never occurred to me that you should adjust the torque you apply if you use anti-seize on bolts.

    Here's a link to the page - RockAuto July Newsletter :: Early Edition

    Here's the article I've ripped from that page in case it goes away:

    My Garage Experiment

    I tend to put anti-seize compound on most bolts. After struggling to remove a frozen fastener, I want to make sure that it is easier to remove the next time. I have read that the problem with smearing anti-seize compound on nuts and bolts is that it makes it too easy to over-tighten even using a torque wrench. The torque specifications in repair manuals are usually written for fasteners that are relatively clean or “dry.”

    The right torque is essential for the success of many repair jobs. Cylinder head bolts sometimes have a torque specification that requires both a torque wrench and a torque angle meter to measure a subsequent rotation of the fastener by a set number of degrees. Fel-Pro recommends that a “torque-to-yield” cylinder head bolt never be reused because “chances are great that it has already exceeded its elasticity barrier and won’t spring back to properly seal the engine.” What if even the most careful torque measurements on new parts using the best tools is thrown out the window by a dab of anti-seize compound?

    I decided to clear off a corner of my workbench for a quasi-scientific investigation! I cleaned a new bolt, washer and nut to make them “dry”, clamped the nut in a vise and marked the position of the bolt head at points between 25 to 65 ft. lbs. of applied torque (34 to 88 Nm). Then I put anti-seize compound on the bolt and measured the torque necessary to bring the bolt head back to the dry positions. With the anti-seize compound, I found that 31% to 44% less torque was needed to turn the bolt head to the dry position. For example, 45 ft. lbs. of torque on the anti-seize coated bolt turned the bolt head as far as 65 ft. lbs. of torque on the dry bolt. The dry/anti-seize conversion ratio became very non-linear when I put 65 ft. lbs. (88 Nm) of torque on the anti-seize covered bolt. The bolt head turned far past (remember this is quasi-scientific!) the dry 65 ft. lb. mark indicating that the bolt head was probably now cutting into the washer and/or the bolt was stretching.

    [​IMG]

    After my experiment, I looked at bolt manufacturer data and found they generally recommend roughly 25% less torque (compared to dry) on fasteners lubricated with anything (oil, grease, etc.) and roughly 40% less torque on fasteners coated in anti-seize compound.

    I am still a big fan of anti-seize, but I am going to more carefully consider the torque specifications for each bolt. Many, if not most, of the bolts I install are hard to access and impossible to get a torque wrench on. Most fasteners have likely been inadvertently lubed by the penetrating oil I used to help remove them, transmission fluid, the grease on my gloves, etc. With those hard to get to bolts, I can only use the manufacturer torque specification as a ball park figure to calibrate the pressure I feel in my hand and wrist when I turn the wrench. Manufacturer torque specs in the repair manuals are usually a range rather than an exact number so now at least I know to usually aim for the low end of the torque range.

    I will forego the anti-seize compound and/or follow the part manufacturer’s installation instructions when I work on torque sensitive sealing applications like cylinder heads. It is worthwhile to remove more parts so the torque wrench has access and make an extra effort to clean fasteners and mounting holes. I will also be more cautious when bolting together dissimilar metals like aluminum to steel. My garage experiment showed me how easy it would be to inadvertently distort or crack parts while tightening lubed fasteners to the high end of a torque specification range. My test bolt looks the same to me, but it likely painfully “exceeded its elasticity barrier” when I applied the anti-seize compound and 65 ft lb. of torque.

    Tom Taylor,
    RockAuto.com
  2. NLXTACY

    NLXTACY Mud Life Sentence SILVER Star

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    This is well known by engine rebuilders.
  3. 86tuning

    86tuning

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    ^^ And all ASE techs. That's why internal engine fasteners are only lubed with engine oil.

    And why diff side bearing preload ring threads are best lubed with anti-seize.
  4. Rwhat

    Rwhat

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    Learned this in torque training class yeas ago. NASA has a chart that calls out the torque of bolts. The chart takes into account the Bolt size, material, lubed threads or dry, ect. Not to mention torque patterns and running torque. There is alot of science and engineering behind fasteners.
  5. landtank

    landtank SILVER Star

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    you got one of those fancy charts that takes rust into consideration?
  6. Tapage

    Tapage Club 4X4 Panamá SILVER Star

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    I'm big fan of torque values .. coz I'm very good breaking bolts .. but to be honest more than 60% of the bolts in my cruisers have just poor access to any kind of torque wrench ..
  7. Rwhat

    Rwhat

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    Nope ;) I don't use them on my own junk. However people don't realize that torque is very important in certain areas of use. Especially those people who like to use the German system of "gut and tite"

    Alot of my stuff I follow the FSM and use a little more torque when I use anti seize. (I use anti seize on almost everything)

    The German method I suspect has failed when used to "tighten" brake caliper bolts.

    When I worked on 501/T56 gas turbine engines we used dry moly lubed mixed with oil for most of the fasteners. Usually in the turbine sections we used anti seize for the thermocouples and misc stuff that took extreme heat. IIRC.

    I never realized how in depth fasteners got. Untill I worked in aerospace with alot of smart anal people with a lot of schooling. Most of the stuff is over my head however I understand some of it since we do a lot of hands on work doing testing.
  8. rove_mcanus

    rove_mcanus

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    A good anti sieze doesn't affect friction much at all.

    It's also important to consider what effect a substance has on friction, ie does it reduce or increase. If it increases friction, then you have to increase torque value to compensate.

    This is why alot of car manufacturers have the torque-turn 90-turn 90 tighten pattern on head bolts, and why factory manuals have tests such as the fish scale pull test on wheel hubs to make sure things are assembled correctly.
  9. fj4068

    fj4068

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    It seems the important question is, for a given torque spec, what was the intent of the engineer? Did the engineer specify it based on avoiding the plastic deformation yield point of the materials involved, or was the intent to achieve sufficient friction to avoid loosening in service?

    It seems that anti-sieze would make it easier to exceed a bolt or its socket's plastic deformation limits, which seems to be the point of Mr. Taylor's article. OTOH, if I put it on something such as a wheel lug nut, should I increase by a certain percentage to avoid loose nuts? It seems that by using something other than a dry bolt, I have been erroneously assuming that it's both safe and necessary to use additional torque.

    In the table below, the wet values are lower than dry values, which I assume are based on yield strength:

    LINK

    Rove_mcmanus, do you have an example of an anti-sieze that doesn't reduce friction? I'd like to see how that differs from my standard PermaTex copper anti-sieze that I slather on rust-prone bolts...
  10. Adam R

    Adam R

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    I did a similar experiment several years ago when I received a lot of negative advice about using never seize on lug nuts. The concern was that people would begin applying it everywhere, to include the friction surface of a cone nut. My slightly more scientific method involved measuring the stretch of the bolt, (staying in the elastic region of the material) but the results indicated that you could over torque by as much as 100% or more if you put never sieze on the friction surface of a cone nut. If you keep the never sieze on just the theads, I back off the OEM torque values about 10% and it's worked just fine for over 20 years.

    Of course, a good calibrated wrist and forearm is always beneficial as well. Many shadetree mechanics have no idea how tight something is suppose to cranked down and proceed until they cannot turn it anymore or it breaks, whichever comes first.

    Adam
  11. fj4068

    fj4068

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    A few quick reads:

    http://www.intermotive.net/Tech Tip/Tech Tip - Jan 08.pdf

    Mechanical engineering other topics - Dry or Wet fasteners (re:thread404-173061)

    Torque - Torqueleader (PDF downloads at top right)
    -------------

    In a nutshell, anytime the threads are dirty, rusty, oily or coated with thread-locker or anti-sieze compound and the spec doesn't call for that condition, then we are whistling in the dark about the proper new torque spec unless we're equipped to test for yield and/or clamping force. We can choose to reduce the torque value by XX%, but this may allow the fastener to self-loosen in service. Conversely, if we tighten to spec'd dry torque value while lubricated, it may exceed yield strength or strip soft threads.

    Adam R, what do you mean by the friction surface of a cone nut? Are you talking about the contact interface area between it and the rim?

  12. LINUS

    LINUS Waiting for the Great Pumpkin

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    I know it's not exactly scientific, but at least for my own use I take into account the size & thread pitch & on smaller stuff reduce the TQ value by ~10% - on bigger & coarser threads i just run the Spec'ed value - I have run by that for over 20 yrs & it's always got me by & never had something come loose on my junk. Plus, you need sieze in WA unless you want to break rusty bolts all afternoon.
  13. landtank

    landtank SILVER Star

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    I always fall back on the tried and true procedure of torque to snap. You basically tighten the bolt until it snaps and then back it off a 1/4 of a turn.
  14. NLXTACY

    NLXTACY Mud Life Sentence SILVER Star

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    ^ Really is foolproof.
  15. 86tuning

    86tuning

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    Well my old master techs used to say to NOT tighten it until it goes loose again. Lol.

    As for wheel lug torque, we just stick to 76# wet or dry for washer nuts. And 85# for cones.
  16. PabloCruise

    PabloCruise SILVER Star

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    Good read...
  17. ybhc

    ybhc

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    I've never lost a brake caliper, never snapped a caliper bolt, and never used a torque wrench on a caliper.

    Excuse me while I go find a large wooden beam to rigorously tap.

    But really, the only things I use torque wrenches on would be anything inside the engine/transmission/TC (except for the driveshaft bolts which get german'd) at their inputs/outputs, and just about everything on the axle.

    even my wheel lugs get done by feel. Never lost a wheel either.

    If i used a torque wrench on every single bolt like the FSM told me to, I feel like I'd spend 50% of my time twisting my torque wrench handle, 40% trying to wrestle it into place, and 10% actually getting something done.
  18. CruiseOrlando

    CruiseOrlando Conveniently Enhanced SILVER Star

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    That's why I have one of them there fancy-dancy e-lec-tron-ic torque wrenches!
  19. mattafact

    mattafact

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    I used antisieze on my flywheel bolts on my 22r. Any danger in that?

    I havent even put the clutch on yet so I could remove it if it's going to cut me in half or kill a bus load of nuns, etc.
  20. 86tuning

    86tuning

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    If I put anything on flywheel bolts, it's red loctite 262, just like you'd see on many factory fasteners used for flywheels.

    If I were you, I'd carefully clean off all the anti-seize compound with some brake cleaner and compressed air, or a whole lot of paper towels and brake cleaner.

    Loctite is your friend for bolts that you do NOT want to come out. Flywheel bolts would be at the top of my list for bolts that I don't want coming out.

    Think of how close to your ankles the flywheel is, spinning at 5000 rpms and then letting go.... 25 lbs of mass, with gear teeth on the outside.

    There's a reason that SFI specifies reinforced bellhousings on drag race cars!

    Nevermind the bus load of nuns. Think of how hard it would be to walk if you're missing part of your feet. Or push on the gas pedal :p

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