mech1,
I can count on one hand the number of angle-tightening heads that I have been involved in removing, so I am not sure I should be querying what you say. However, I recall heads where the Torx screws are recessed and it is impossible to get at them with a 1/2" drive. I have used a 1/2" to 3/8" adaptor with no problem at all, and the adaptor is a very cheap one from a local discount accessory store.
I don't understand why you say that the socket extension bar should be at least 300mm from the head. Do you mean to avoid injury to your hand? I find it best for the socket extension to be as short as possible. I think you have more control with a short extension and can apply more force. I agree that your hands need to be clear of the head in case the bolt turns suddenly or the tool slips, but 300mm above it?
Thirdly, I know that most 'stretch bolts' must never be re-used but I wonder if this applies to K-series bolts? If the stretch is applied over a very long length there might be no danger of the bolts having been taken beyond their elastic limit. I'm not saying that this *is* or *isn't* the case ... just wondering.
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Jambo, are you having problems removing just one of the bolts or all of them?
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When I undid the (stretch) head bolts on my BX TD I needed all of a 3ft bar and my not inconsiderable bulk to 'break' them. Citroen do not make it easy as there is no direct access to some of the head bolts so I had to use a 'wobble' bar to get in there. A 3/8" drive will take a lot of force before it breaks if it's a decent one. Tightening them up is a bit odd - it's hard work getting the angle turn on, and then you can feel them stretch - the bolt continues to turn, but doesn't need much more force - makes you think they're about to snap off / strip the thread!
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RichardW
Is it illogical? It must be Citroen....
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Dizzy
Stretch bolts by definition do go beyond the elastic limit, and normally, as you say, should not be reused. By taking the bolt into the plastic region of the load/extension curve they apply a controlled load to the head/block joint. Trying to reuse them takes them too far into the plastic region, and the load they apply will drop, possibly dramatically, depending upon their material proerties.
However, Dizzy, your comment may have been stirred by the same memory as I've just had. On the K series, which does have long stretch bolts down to the crankcase, didn't Dave Lacey (a Rover specialist) say here that these could be reused provided the stretch section had not gone beyond a certain length? It obviously needs some definite information and careful measurement, by micrometer or vernier as we're talking very small extensions. I'd suggest checking with a Rover dealer once the bolts are out.
Regards
John S
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its done! thanks again all. following the advice i bought a breaker bar and it didnt need much force from there on. the breaker bar was about 1 foot long. so i can assume from there that head bolts are even tighter on other models. once a full turn had been completed the bolts could be loosenned by hand - which makes me wonder if the bolts were as tight as they should have been, but thats another thread!
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John,
My ancient memory is telling me that stretch bolts should never be taken into their plastic region. They are stretched into 'yield' which is situated in a narrow margin between the elastic and plastic phases. That's not to say that they will return to their original specification when undone; in fact I would be surprised if they do, having been taken to the very margin of plasticity.
My comments about the K-series possibly being different was based on the fact that more stretch can be obtained on long bolts than on short ones, therefore the K-series bolts *may* not need to be taken into yield and therefore *may* not need renewing every time. If that is indeed the case, then what DL says sounds very feasible.
When our diesel engine company introduced angle tightening many years ago, a closely defined yield point could be achieved only by adding Boron to the steel composition. This non-torque system overcame many problems, including the avoidance of different clamping loads depending on surface finishes and level of lubrication; also the need to re-torque after a period of running. I think it was a bigger step forward than was generally appreciated.
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Dizzy
It's a fine point, and I'm sure you're right they don't go far beyond the elastic limit. If they did it would be hard to guarantee clamping load ad the load/ extension curve would be dropping rapidly. However, by definition, once they exceed yield and don't return to the original size then that is plastic deformation.
Regards
John S
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cant comment on what you have done.I said 300mm to prevent any harm to you plus it would be nearer to your possible height ie the most pressure is applied at close to or near your height.bent over the engine and using force usually will not give max force.as far as I am aware stretch bolts should never be reused but then that is up to you.could mean replacement of head gasket and bolts thats without any further damage if you see what I mean.think you was lucky in releasing them though. wish all were the same?
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Rover K Series head bolts are initially torqued to 25nM, then spun 180 degrees in turn and then another 180 degrees. Quite suprisingly, this doesn't feel that tight when doing this.
I've never had one of these bolts snap or shear or even refuse to undo - you do need a breaker bar to initially shift them. Really, a 1/2" rather or T Bar should shift them.
Now, from memory (I could confirm if required) the way of telling is a bolt is fit for service is to measure a section (fat, top section) of the bolt - if it is more than 91mm it is NOT fit for use.
A set of these bolts will cost you around £100 - I've yet to have to replace a set...
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groups.msn.com/honestjohn - Pictures say a thousand words.....
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