Technical 1.6 16v gasoline head bolts stretch bolts or not?
- Thread starter Arlo
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Technical 1.6 16v gasoline head bolts stretch bolts or not?
What vehicle is this in? I wasn't aware that FIAT made a 1.6 16v petrol engine :chin:
If my memory serves me correctly stretch bolts do not have to be renewed on every use. They are good for a limited number of torque cycles. They are designed to stretch and provide a designed retraction/clamping force just like an elasctic band.
Again from memory stretch bolts are torqued to a set value (in sequence) and then one or two stages of angular turns.
Non stretch bolts, at least on cyclinder heads, are normally be replaced.
Again from memory stretch bolts are torqued to a set value (in sequence) and then one or two stages of angular turns.
Non stretch bolts, at least on cyclinder heads, are normally be replaced.
PS
Back in the days of Marina, Mini, etc, (BMC A/B series) We always reused head bolts/studs. Then along came stretch bolts, which as I understand it are tightened into their "elastic range" so tightened to the point of deformation? - and our boss decided that he wasn't going to chance having to redo any job because a bolt fails just because he was trying to save a few "bob". Stretch bolts being used not just for head fixings of course. I also subscribe to this point of view - why risk the possibility of having to "do it all again" or maybe suffering catastrophic damage with the potential of a considerably more expensive bill to sort out, just because you were too mean (and we Scots are supposed to know about being mean aren't we?) to buy a set of bolts? Even if a bolt snaps as you tighten it, although perhaps you're not going to suffer an overheated engine, you're going to waste time taking the head off again to get the broken fixing out and then the block threads are going to be stressed through another, unnecessary, tightening cycle. So I myself, would always renew stretch bolts (feardy me).
If you are doing a head job something that very few people ever check for is "pulled threads" in the block. I first became aware of this phenomenon when I was in my Hillman Imp era - Imps had/have aluminium cylinder blocks so are particularly prone to this problem. What I'm talking about is that sometimes the threads will be pulled up proud of the block surface by a very small amount which will affect the clamping action when the head is torqued down and, if bad, can give you early warning of a thread that is likely to strip on tightening. It's easy to check for. With the studs/bolts removed lay a fine flat file on the surface of the block and rub it lightly to and fro. Remove the file and look at the holes. If there is a bright ring round the hole then the thread is pulled. If it's only a small ring you will probably get away with slightly chamfering the edges of the hole using a large drill bit. If it looks visibly pulled before you use the file You're probably best to helicoil it. I remember working on an engine once where I noticed when checking for this that the threaded holes, all of them, had been "relieved" by drilling out the top millimetre or so of thread - thus the thread started just under the surface of the block. It looked very professionally done so I think it was part of the manufacturing process, I thought it was a good idea. On the Imps, if you were building any thing other than a "stock" motor, it was common to automatically helicoil the threads and to make sure the helicoils were installed just below the block face.
Here are a couple of links to get you thinking. The second also brings up the subject of angle tightening vs torque tightening which I hope you may find interesting.
https://en.wikipedia.org/wiki/Torque-to-yield_fastener
PS Just love that torque wrench - never seen one that looks quite like that, have you? BMW really know how to take the money off you don't they?
Back in the days of Marina, Mini, etc, (BMC A/B series) We always reused head bolts/studs. Then along came stretch bolts, which as I understand it are tightened into their "elastic range" so tightened to the point of deformation? - and our boss decided that he wasn't going to chance having to redo any job because a bolt fails just because he was trying to save a few "bob". Stretch bolts being used not just for head fixings of course. I also subscribe to this point of view - why risk the possibility of having to "do it all again" or maybe suffering catastrophic damage with the potential of a considerably more expensive bill to sort out, just because you were too mean (and we Scots are supposed to know about being mean aren't we?) to buy a set of bolts? Even if a bolt snaps as you tighten it, although perhaps you're not going to suffer an overheated engine, you're going to waste time taking the head off again to get the broken fixing out and then the block threads are going to be stressed through another, unnecessary, tightening cycle. So I myself, would always renew stretch bolts (feardy me).
If you are doing a head job something that very few people ever check for is "pulled threads" in the block. I first became aware of this phenomenon when I was in my Hillman Imp era - Imps had/have aluminium cylinder blocks so are particularly prone to this problem. What I'm talking about is that sometimes the threads will be pulled up proud of the block surface by a very small amount which will affect the clamping action when the head is torqued down and, if bad, can give you early warning of a thread that is likely to strip on tightening. It's easy to check for. With the studs/bolts removed lay a fine flat file on the surface of the block and rub it lightly to and fro. Remove the file and look at the holes. If there is a bright ring round the hole then the thread is pulled. If it's only a small ring you will probably get away with slightly chamfering the edges of the hole using a large drill bit. If it looks visibly pulled before you use the file You're probably best to helicoil it. I remember working on an engine once where I noticed when checking for this that the threaded holes, all of them, had been "relieved" by drilling out the top millimetre or so of thread - thus the thread started just under the surface of the block. It looked very professionally done so I think it was part of the manufacturing process, I thought it was a good idea. On the Imps, if you were building any thing other than a "stock" motor, it was common to automatically helicoil the threads and to make sure the helicoils were installed just below the block face.
Here are a couple of links to get you thinking. The second also brings up the subject of angle tightening vs torque tightening which I hope you may find interesting.
https://en.wikipedia.org/wiki/Torque-to-yield_fastener
PS Just love that torque wrench - never seen one that looks quite like that, have you? BMW really know how to take the money off you don't they?
Last edited:
Sorry guys ... bad hair day :yuck:
My post should have read:
My post should have read:
s130 said:
