Oooolllllllld asbestos head gaskets
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Thread: Oooolllllllld asbestos head gaskets

  1. #1
    VIP Sponsor 59 Floride's Avatar
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    Default Oooolllllllld asbestos head gaskets

    Guys, what's the general thought about re-torqing very old, new stock, asbestos and copper foil head gaskets. I would imagine somewhere in the vicinity of 100 miles but does it need to be done a 3rd time?

    Is there a general rule of thumb..?

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    1000+ Posts geckoeng's Avatar
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    Mr Floride,
    When it gets hot for the first time in the workshop and at abot 1500km/1000Mls, and if it is still going at 60000km again. I never undo bolts to re-torque, just straight to the required torque. And a light smear of oil on your hands on the bolt threads when first assembling.

    Real old school and it still works today. I use Hilomar (?) spray on shim gaskets if you are looking at decreasing compression.

    Ray
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    Ray geckoeng

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    Thanks for the confirmation Ray.

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    1000+ Posts alan moore's Avatar
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    We have had the chat about Hylomar in another thread, but particularly on old head gaskets I like to use the spray on Hylomar.. Yes, I would retension it after a short time, say up to temp twice, and then after maybe 2000 Klm, but leave it after this. I do crack (undo) each bolt in turn, before retensioning it.
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    1000+ Posts robmac's Avatar
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    I'd crack the bolts before re-tensioning.

    On the basis it clears the threads and the torque reading will likely be more accurate

    Previously, I loosened the bolts off to a 1/2 mm clearance between the cylinder head/ bolt head. Relying on the hylomar to keep the head sealed and never experienced a problem. Then do a 2 stage re-torque. Since hylomar stick like sh*t to a blanket I'm had no problems.

    These days, based on the advice of many others I'd just crack them.
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    There has always been a difference in opinion regards crack or not crack the head bolts before re tensioning. After considering the experience of those offering the advice I chose to follow the advice offered by a guy who has built many long distance race engines that have outlasted the opposition. His opinion was based on experience with various alloy block, steel liner engines including 807 type Renault engines, FVA Ford, Cosworth DFV F1 engines, Repco Brabham V8, Chev alloy block V8 and V6 plus Porsche 935 Turbo. The advice was to just tension it up, don't back off the bolt before re-tensioning. Based on my experience after following that advice, I agree with Ray on this one.

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    Thanks Guys, a re-torque without cracking it is .

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    Have a crack at that
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    Hi
    I cannot offer experience on that vast range of engines racing or not. But not cracking the bolt by backing off first flies in the face of a lot of advice and my experience. Sometimes the bolt does not move what then ?? I do one at a time in the correct order.
    It will depend on the preparation done before the assembly and then how the threads have adhered to each other. A very variable unknown IMHO. Whereas just backing it off a quarter turn say so it moves and then moving continuously to the retension setting in a smooth continuous motion sounds good to me.
    In a previous life, I have spent some weeks in several sessions looking at the tensioning of roof bolts to compare torque settings to actual direct bolt tension, and the variability due to thread fits, and also the effect of different spec washers including roller thrust bearings. And I could comment it is not straight foward to see the variables that affect the actual tension in the bolt.
    That is why they moved to angular setting into the bolt yield, as the yield strength of the bolt is a much more consistent thing to predict.
    My three cents worth Jaahn
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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jaahn View Post
    Hi
    I cannot offer experience on that vast range of engines racing or not. But not cracking the bolt by backing off first flies in the face of a lot of advice and my experience. Sometimes the bolt does not move what then ?? I do one at a time in the correct order.
    It will depend on the preparation done before the assembly and then how the threads have adhered to each other. A very variable unknown IMHO. Whereas just backing it off a quarter turn say so it moves and then moving continuously to the retension setting in a smooth continuous motion sounds good to me.
    In a previous life, I have spent some weeks in several sessions looking at the tensioning of roof bolts to compare torque settings to actual direct bolt tension, and the variability due to thread fits, and also the effect of different spec washers including roller thrust bearings. And I could comment it is not straight foward to see the variables that affect the actual tension in the bolt.
    That is why they moved to angular setting into the bolt yield, as the yield strength of the bolt is a much more consistent thing to predict.
    My three cents worth Jaahn
    I believe the effectiveness of the process of re-tensioning head bolts is largely governed by how well the bolts/ holes were prepared and lubricated in the initial fitting. If this was done properly.

    The remaining major unknown is being aware if any foreign material ie hylomar or coolant has made it's way into bolt threads.

    For the sake of the exercise I have ignored any damage that may have happened during the initial tightening.

    Angular tightening may address the above.
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    1000+ Posts Beano's Avatar
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    I can't see why cracking the bolts by backing them off just 1/8 of a turn could hurt. Otherwise you are just progressively tightening it to higher torque each time....which I suppose is OK if you first do them up a little low...
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    Can anybody say that they have loosened a head and not one of the bolts had that initial bite in it? That bite is so positive that you can feel it by hand that you need more power to overcome it and then after that, it becomes normal to the touch you have with the wrench you are using. That bite is the same bite that is going to prevent the torque wrench from clicking when re-torquing because that bite is there for either tightening or loosening a head bolt.

    I believe in cracking them loose about 20-30 degrees. I don't know how other people assemble engines but I have always had the bolts or some of the bolts free to torque and others had a bite in them. That bite can prevent the re-torque to tension it to spec. I don't know where the bite comes from but I'll bet my bottom dollar that if you need a fraction of rotation on the bolt to get the torque to spec, that bite will hold it and then you will be thinking that it is ok. Then if you loosen it 20 degrees and re-torque it then, you will need 20+?? degrees before the click is heard.

    I know that I'm not a motor mechanic and never will be, but things like I said above has so much common sense for me that it will need a very good explanation to change my mind.

    Frans.
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    Well said, Frans...

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    Hope Genevieve hasn't needed this work!! Phil Harrison has another take on this technique, FYI.

    My experience with the copper-asbestos gaskets has been that they take up a surprising amount, especially on the exhaust side of the head.

    My quite different issue with them is that modern coolant seems to leak through the asbestos layer! Lower surface tension than water and no sludge formation to seal the gasket properly!! I have a few old 4CV ones in the gasket drawer....
    JohnW

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    II think I've been here before. My experience has been mainly with the 2 litre 'open block' 504 and the PRV 6. These required a three stage tensioning with a final degree tightening.. It was necessary with any re-tensioning to back off the bolts individually.
    My rather "woolly" theory is that backing off the bolt eases the "stickacity" [my word] of the thread allowing for a smoother retensioning.
    I believe most manufacturers have adopted the later torque to yield, the bolts being necessary to renew every time.
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