Head Bolt Re-torque

Discussion in 'Inboards' started by mikealston2428, Dec 29, 2014.

  1. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Hi All,
    I have a rebuilt Chevy 350 with cast iron head and ARP head bolts.
    Do I have to re-torque ARP bolts after initial start up ??
    If the answer is yes how many hours after first start should this be done ??
    Also do I need to re-torque the exhaust manifold ???
    If i do is this done at the same time as head bolts ??
    What is the prosedure for re-torquing do you back them off them torque or just torque ???
    Thanks,
    Mike
     
  2. mikealston2428
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    mikealston2428 Senior Member

    I used Felpro head gaskets
     
  3. gonzo
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    gonzo Senior Member

    If you used any of the "permatorque" gaskets, they don't need re-torquing. However, if what you bought was some old style, they may. What did the package say?
     
  4. whitepointer23

    whitepointer23 Previous Member

    I always wait till the engine is stone cold and retorque regardless of which gasket I use. Probably don't need to but its just how I was taught.
     
  5. WestVanHan
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    WestVanHan Not a Senior Member

    I'd say redoing them is a good idea-in my case anyways-as one may get distracted and forget one....or three.
     
  6. gonzo
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    gonzo Senior Member

    Not really. A modern gasket is designed to be crushed by the first expansion by heat. It then retains enough elasticity to recover from the temperature changes. Re-torquing it takes all those qualities away by crushing it too much.
     
  7. PAR
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    PAR Yacht Designer/Builder

    It depends on both the gaskets and the bolt type. Torque to yield bolts don't get re-torqued. If these are the standard Motown head bolt kits from ARP, then you don't need to re-torque, but you can if you want, as these are "fatigue resistant" style of fasteners. Torque to yield bolts, like those from the factory aren't fatigue resistant and will stretch and not spring back when loosened, so you can't re-torque these (they're stretched).

    Gonzo is right about the head gaskets too, they're designed to suck up with initial heat cycles and shouldn't be re-torqued.

    Exhaust manifold bolts also can be torque to yield, but they usually aren't, so yes, you can re-torque these. Exhaust bolts just seem to come loose, even with thread lock compound. They do make special exhaust bolts with locks, so they can't come undone. In most cases, you just re-torque occasionally, to insure they're where they need to be.

    All this said, sometimes the parts don't seat right with the first go around, so it's common practice to "sneak up" on it, with progressive rounds of torquing. If the spec is 55 pounds, then most will torque to 40, then 45, then 50 and finally 55. Lastly no, don't back off the bolts, just go around in sequence and hit the torque spec. In all likelihood, your bolts will all be where they're supposed to be. The real key to proper torque is clean threads and good lubricant.
     
  8. whitepointer23

    whitepointer23 Previous Member

    Gonzo and par show us an example of a head gasket failing because it has been retorqued. Sounds like a tall story to me. I have never heard of it anyway.
     
  9. PAR
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    PAR Yacht Designer/Builder

    A gasket failure rarely gets examined very closely, unless it's the NTSB. If your head gasket takes a dump, the signs are usually obvious and it's simply replaced. As to re-torquing them, just look at the manufacture's sites and you'll see no re-torquing recommendations. Knowing how their made makes their recommendation reasonable.
     
  10. gonzo
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    gonzo Senior Member

    If you follow the manufacturer's instructions there is a warranty backing the product. Otherwise it is void. Whitepointer23: do you offer any assurances that your method is better than what the manufacturer's research recommends?
     
  11. whitepointer23

    whitepointer23 Previous Member

    Only that I have never had a problem and the engine rebuilder that told me he does it has owned a respected reconditioning workshop for 30 years. You obviously don't have knowledge of it being a problem either or you would have told us.
     
  12. whitepointer23

    whitepointer23 Previous Member

    I am not trying to start a fight . Its just something that I have not had a problem with.
     
  13. PAR
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    PAR Yacht Designer/Builder

    I know lots of folks that are long established whatever's and are behind the curve on some stuff. Hell, I'm one of those too.

    In recent years, mostly since the advent of torque to yield fasteners, gasket manufactures have had to address a single torque situation. In other words, the builders don't want to have to re-torque anything, so to address this and still insure performance, the manufactures have developed material combinations that crush once and stay put.
     
  14. Moggy
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    Moggy Senior Member

    That is not always the case, if the bolt measures to spec after use it can be reused in many cases. I have done so on many occasions. They are elastic and need to be and remain so to perform the task, the loss of elasticity is more the issue. They are trying to make us believe that many things that are in fact reusable are not. Subaru's latest aircon belts fall into that category, they swear blind that they must be cut and replaced with a new "stretch belt"... pure BS by my experience, easy to reuse an undamaged belt.
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Just because you have "gotten away" with some unrecommended techniques, doesn't make them any more valid, just lucky. Your description of a torque to yield bolt is incorrect. They aren't elastic, which is the point. Regular bolts are and will stretch under torque and return to length when released, but a torque to yield fastener doesn't fully return to length, therefore can't be trusted to be re-torqued. They're designed to "set" at the torque and they do. I'm measured way too many bolts, on high output application to even think about trusting one that's been tweaked to it's torque range.

    The bottom line is you need to understand what's really happening with a torque to yield fastener. The first thing is they are intended to (calibrated) elongate to a specific length at a specific load. Once at this they've reached their plastic deformation limit and this is key. If this style of fastener is backed off and re-torqued, you'll exceed this plastic deformation point and the fastener is not going to hold, because you've screwed it's molecular bonds to some degree. In low load applications, you might get lucky with a bolt, but you can bet a re-torqued TTY fastener has passed it yield and fracture is the usual outcome. These fasteners were designed to offer more uniform clamping pressure, particularly with machine tightened fasteners on the assembly line. This is so true, that gasket manufactures usually supply a new set of TTY bolts with a quality head gasket set. Now why would they be willing to lower their margin on a product, if they didn't have to? No bean counter in the industry worth his calculator, would survive this type of logic, unless it was necessary.
     
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