head re-torquing
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default head re-torquing

    I dont really know much about head gaskets, and the reasons you would or would not re-torque the head, and was hoping some of the guru's who really understand the function of this process might share some wisdom as many of us enthusiastic amatures do our own head gasket changes and rely on sometimes hopelessly abbreviated information like might be found in a haynes book of lies.

    I remember one of my first fuego head gaskets did not last long on its original installation.
    Now I do a re torque after a few hundred km, but dont really know whats happening with the gasket when I'm doing this.


    One question that I have is when the say..20k km old gasket has breached in some way and showing bad signs, as well as adding chemi-weld products for a nasty short term fix, is there any merit in doing a head re-torque??
    Will this make things better or worse???

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    Jo

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    Icon5 Change the head bolts for new...or not! Big question!

    That was the normal way of re tightening after a short period that I was taught, but since then they have introduced head bolts that are supposed to be one time use and torqued down at a pre set figure.

    IN general the good Fuego book says fit new head bolts each time - most of us don't. I did read up the reasons etc. but found no one seemed to be selling new head bolts anyway, so if you re-use them, best to go through the re-tightening after they settle down IMHO.

    If the gaskets fail blame the bolts!!

    Ken

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    Quote Originally Posted by jo proffi View Post
    I dont really know much about head gaskets, and the reasons you would or would not re-torque the head, and was hoping some of the guru's who really understand the function of this process might share some wisdom as many of us enthusiastic amatures do our own head gasket changes and rely on sometimes hopelessly abbreviated information like might be found in a haynes book of lies.

    I remember one of my first fuego head gaskets did not last long on its original installation.
    Now I do a re torque after a few hundred km, but dont really know whats happening with the gasket when I'm doing this.


    One question that I have is when the say..20k km old gasket has breached in some way and showing bad signs, as well as adding chemi-weld products for a nasty short term fix, is there any merit in doing a head re-torque??
    Will this make things better or worse???



    Jo
    I think the rule of the thumb is re-torque non-stretch bolts, don't re-torque stretch bolts. Stretch bolts tend to be the ones where the instructions say torque to a given figure and then turn an extra half turn or something like that.
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    I'm an automotive machinist in my final year as an apprentice. Apparently gasket materials have changed alot and re-torquing is not used with "torque-to-yield" stretch type bolts and compound graphite/MLS gaskets used in modern vehicles. We do re-torque older stuff. It seems to be mostly cast-iron cylinder heads that require re-torquing. When you re-torque, it pays to knock the top of each head bolt with a copper/wooden drift before you re-tension it.

    For the record, our engineer manual for the Fuego 829 (1994cc) engine recommends the following procedure:

    1) 20 Nm
    2) -90 degrees
    3) 20 Nm
    4) +105 degrees
    5) +105 degrees

    This would indicate that you do not need to re-tension the head bolts, as there would be no way of telling where +105 degrees should be as the final position. Also with that much torque, I'd be looking for replacement head bolts.

    Another option if they aren't available would be to accurately record using a tension wrench and a degree wheel the actual increase in Nm the 105 degrees applies at steps 4 and five. Then you could set your wrench to that figure and after a few hundred Km check the tensions. The bolts will fail after two or three uses though.

    I have been taught that once a gasket fails it's irreparable, so no amount of re-tightening will help.

  5. #5
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by chez00 View Post

    1) 20 Nm
    2) -90 degrees
    3) 20 Nm
    4) +105 degrees
    5) +105 degrees
    Wow, never seen that before.
    Thanks for the reply (and everyone else too)
    I just torque them up in two steps to an amount (forgotton the amount 60bl/f??) and that is it, then do it again a week later.

    Touch wood, so far so good.


    Jo

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    1000+ Posts Frans's Avatar
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    Hi,
    My understanding is the same as chez00 and Uffee. What basically happens is that when you torque a head on the bench then it is cold and hard. After a few times of heating and cooling the gasket will "collaps" because by now it has sort of annealled itself (gone soft). This is why you have to re-torque the bolts. If you have stretch bolts then the tension of the stretch bolts will take up the "collaps" effect of the gasket and no further torquing is needed.
    Maybe there is a change in your engine models, old with normal bolts and later with stretch bolts? The only way to identify some of them is that the normal bolts looks normal all along the shaft and stretch bolts is slightly thinner at the smooth shaft area (shank).
    I re-torque competition wet sleeve engines up to 4 times when they have normal bolts. Loosen them about 30 degrees when cold and then you will notice that with the 1st torque the T-wrench will go past the 30 degrees up to 45 degrees before it clicks. The 2nd torque less and so on.
    Regards
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  7. #7
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    Default Brown underpant moments.....

    Frans
    All the Fuego ones I've seen are the necked in shaft, and when you tighten them with a torque wrench ,, they give an almighty cracking sound as they bed down. That noise frightens the daylights out of older style engine fiddlers, the first time they come accross it. !

    You reckon they have snapped when they do that!! Touch wood, like Jo, no problems so far!! I meticulously clean the carbon off the threads and any oil seep that is sitting in the thread holes, and lightly lube then before tightening. But then I'm an old fusspot!

    Ken
    Last edited by Kenfuego; 14th February 2011 at 08:07 PM.

  8. #8
    1000+ Posts Frans's Avatar
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    Thanks for that Ken, Jo then I am sorry but it sounds like you should re-do it as in the specs above?? Or are going to risk it?

    Frans
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  9. #9
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Frans View Post
    Thanks for that Ken, Jo then I am sorry but it sounds like you should re-do it as in the specs above?? Or are going to risk it?

    Frans
    Oh shite, why did I start this thread. Now my head gasket is going to breach.
    Nah, i'll risk it. The last job lasted 70k on the silver car before I wrote it off, and this car cops just as much grief and is belting along perfectly, so if it aint broke, I'm not touching it.
    I have great confidence that my head is set right in spite of the maybe less conventional way of doing it.

    Can someone help me understand what this means, just in case though.

    For the record, our engineer manual for the Fuego 829 (1994cc) engine recommends the following procedure:

    1) 20 Nm
    2) -90 degrees
    3) 20 Nm
    4) +105 degrees
    5) +105 degrees
    step 4+5 are obvious, but 123 have me confused.

    Jo

  10. #10
    1000+ Posts Wildebeest's Avatar
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    Jo,
    My interpretation is...
    [1] Tighten to 20 nm.
    [2] -90 deg. That is..back off 90deg [1/4 turn].
    [3] Tighten to 20 nm.
    [4] Further tighten 105 degrees.
    [5] Further tighten 105 degrees.

    [4 & 5] may need a degree plate or your old school protractor.

    All tightening and backing off to be done from bolt one.

  11. #11
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    Chaps,

    You need to look at the expansion differential of the head material. Alloy heads expand greater than cast iron heads per degree of temperature. Therefore the head gasket is compressed more with alloy heads than with cast iron after the first heat/cool cycle.

    The need to follow up after a run with an alloy head, once it has cooled, is greater than with an iron head, but with regard to factors such as the type of gasket used (indented flat metal, compound, sandwich metal-compound, types of compound - asbestos, non-asbestos, etc), type of fastener (stretch or reusable), wet sleeve liner protusions, accuracy of mating surfaces, and so on.

    Single use stretch bolts are fastened to the elastic limit of the bolt. Once used they DO NOT return to their original qualities. However, if tightened as per NON-STRETCH bolts they can be reused, providing they are never used as stretch bolts.

    Non-stretch use of any bolt will allow retightening, and it may be of advantage to do so in some situations.

    Keep in mind, as a peripheral issue, with overhead cam engines whatever method the head is tightened it is essential that the cam is correctly aligned within its bearings after tightening. Any warpage of the head as a result of improper tightening will destroy cam bearings very quickly.

    Please be careful, and be guided by the manufacturer,

    Regards,

    Fento

  12. #12
    1000+ Posts jo proffi's Avatar
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    wow, there are some insightful posts here, thanks guys.

    Single use stretch bolts are fastened to the elastic limit of the bolt. Once used they DO NOT return to their original qualities. However, if tightened as per NON-STRETCH bolts they can be reused, providing they are never used as stretch bolts.
    That sounds like a good mantra and one I can understand.

    What I dont understand clearly is what constitutes "used as stretch bolts"

    Is this a set of instructions for new stretch bolts???
    1) 20 Nm
    2) -90 degrees
    3) 20 Nm
    4) +105 degrees
    5) +105 degrees
    Jo
    Last edited by jo proffi; 15th February 2011 at 12:01 AM.

  13. #13
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    Jo,

    Sorry, mate,

    To clear the issue some bolts are sold with the instructions that they be tightened to a certain torque wrench setting AND then tightened a further specified number of degrees.

    If so tightened they are then at their 'elastic' limit', and cannot be used again as designed.

    These are stretch bolts, of use to the manufacturer as no follow-up is required from initial fitting.

    However, those that are tightened to a torque wrench limit in two or three steps are generally non stretch bolts, and can be reused. Manufacturer's do not like these due to waranty servicing costs.

    Jo, there are many variables, and there are details for each with the supplier's instructions - please check these and fit accordingly.

    Sorry if I cannot be more specific,

    Fento

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    Quote Originally Posted by fento View Post
    Jo,

    Sorry, mate,

    To clear the issue some bolts are sold with the instructions that they be tightened to a certain torque wrench setting AND then tightened a further specified number of degrees.

    If so tightened they are then at their 'elastic' limit', and cannot be used again as designed.

    These are stretch bolts, of use to the manufacturer as no follow-up is required from initial fitting.

    However, those that are tightened to a torque wrench limit in two or three steps are generally non stretch bolts, and can be reused. Manufacturer's do not like these due to waranty servicing costs.

    Jo, there are many variables, and there are details for each with the supplier's instructions - please check these and fit accordingly.

    Sorry if I cannot be more specific,

    Fento
    Pretty hard to be more specific on a general matter Fento, so that's nothing to apologise for!

    Lots of changes over the years in gasket material, sleeve base seal systems, OHV versus OHC heads AND the stretch bolt issue.

    I do know that if I worked on a stretch bolt head, I'd be very worried if I did NOT change the bolts from what I have read over the years.
    JohnW

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  15. #15
    bob
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    G'day,

    Quote Originally Posted by fento View Post
    ........However, those that are tightened to a torque wrench limit in two or three steps are generally non stretch bolts, and can be reused. Manufacturer's do not like these due to waranty servicing costs.......
    this is exactly what was in my mind after the first few posts, it's all about costs Jo, Regie only wants the job done once.

    The situation with us is totally different, we can come back in xkm and play with it again, and again after that if you feel so inclined, assuming that system has worked for you in the past. All the backyarders are in this situation and I'd reckon that Haynes is written with that mantra.

    In olden times, like Ken , you always came back next week and did them all again - each bolt/nut in turn, undo a little then re-torque to the original number. And, we had alloy heads in olden times as well, and alloy blocks in the bikes. However, pretty well all donks had studs, not bolts, at least the ones that I came across did, maybe this is also relevant ? - I always "feel" better about putting the pressure on via a stud that is secure in soft material than a bolt screwing into that soft material.

    Jo, I would suggest that if the revisit system worked for you in the past it will work for you in the future. But, as Ken says, be pedantic about preparation. Maybe we should all get ourselves a nice new set of normal HT bolts for future replacements from your local friendly nut & bolt man - anyone ever thought about using studs on a froggie ?

    cheers,
    Bob
    Last edited by bob; 27th February 2011 at 09:36 AM. Reason: typo

  16. #16
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by fento View Post
    Jo, there are many variables, and there are details for each with the supplier's instructions - please check these and fit accordingly.

    Sorry if I cannot be more specific,

    Fento
    Pretty hard to be more specific on a general matter Fento, so that's nothing to apologise for!
    Agreed.
    Yes, this subject got a little broader than the original post, and all all the contributions have been informative, however it became a huge case of the more you learn the more you realise you dont know.
    I have done heaps of reading since this origional post, especialy since Frans, who I have a gread deal of respect for in regards to engine stuff posted this.

    Jo then I am sorry but it sounds like you should re-do it as in the specs above?? Or are going to risk it?
    This gave me plenty to think about, because risking it is always an easier decision to make if the risk can be calculated, so I went back to all my written documentation.
    Haynes book of lies say torque up to 88-98 Nm, without giving any any further detail except the order of tightening. This is what i have always done.

    All the Renault MR documentation for all the dourvins have an angle method.

    More general reading suggested that the main difference between the' torque only' and the angle method came down to the deviation in 'actual' torque of the fasteners from the readings taken at the torque wrench, and that that the end of a non angle torque down the variation could be huge.

    Being someone with far too much time on their hands, the bolt thread holes were very clean and the bolts well lubricated
    I never had any cracking on instalation, and hopefully without staring a fresh debate on this subject, I have a decent idea on the feel of fasteners.
    I'm not suggesting I can 'feel' torque or am a modern day Uri Gellar, but if there is a human scale with a gorilla with a rattle gun at one end and a violin player at the other, i think I'm more up the violin side of things.
    I have enough confidence in what i can feel as the bolt tightens to reach the conclusion that I have tightened each bolt within an acceptable range of torque.
    70k hard km with this head on the last donk and 20k equally as hard km on this motor without an issue would suggest that the torque only method with old bolts works fine.



    this is exactly what was in my mind after the first few posts, it's all about costs Jo, Regie only wants the job done once.

    The situation with us is totally different, we can come back in xkm and play with it again, and again after that if you feel so inclined, assuming that system has worked for you in the past. All the backyarders are in this situation and I'd reckon that Haynes is written with that mantra.
    I'd believe that.
    Whilst I have the confidence in my head install, you'd not want to be charging for the job, it is slow.

    Jo

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