Torque Angle Gauge
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You realise this is just an angle gauge, and the torque setting has to be applied first, of course!
(Not trying to be patronising here)
John
(Not trying to be patronising here)
John
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To be honest they're all a bit fiddly to use, well any I've tried.
Just a suggestion: If you wanted to Tipex both the head bolts the cylinder head (as John says after you have preloaded the bolts with the torque wrench). If the angles are 30, 60 or 45 degrees you can watch the mark on the bolt in relation to the mark on the head. For example one face on the bolt will be 60 degrees, if you get my drift?
Just a suggestion: If you wanted to Tipex both the head bolts the cylinder head (as John says after you have preloaded the bolts with the torque wrench). If the angles are 30, 60 or 45 degrees you can watch the mark on the bolt in relation to the mark on the head. For example one face on the bolt will be 60 degrees, if you get my drift?
Lol, yes I'm aware the bolts need torquing down first! But it begs the question, why don't the manufacturers just put final torque values alone, like they always used to? I can't see how one way would be any more accurate than the other, relying, as they both do, on torque wrench accuracy albeit at different forces. Are wrenches less accurate at higher torques? If not what's the point?
Think of the bolt as a spring......if it is stretched it can exert more of a clamping force when it tries to retract - but of course overdoing it exceeds the elastic limit or yield of the bolt and it snaps.
Tightening bolts using the degree method is more accurate than using a torque wrench alone.
This is why new head bolts must be used after a rebuild, as they have become stretched first time round, and the tightening force may not be accurate second time or the bolts could snap.
Don't ask me how I know Many other bolts which use a 'pinching' method during their use should be renewed too - especially front strut to hub ones.
John
Tightening bolts using the degree method is more accurate than using a torque wrench alone.
This is why new head bolts must be used after a rebuild, as they have become stretched first time round, and the tightening force may not be accurate second time or the bolts could snap.
Don't ask me how I know
Many other bolts which use a 'pinching' method during their use should be renewed too - especially front strut to hub ones.John
Well we didn't need the degree method in the olden days when I was on the spanners... And we reused the head bolts. A cynic might suspect an artificial backdoor subsidy for the bolt industry. Anyway, I've ordered the cheap Bergen one, hopefully that will do the job. Thanks chaps.
And we reused the head bolts. A cynic might suspect an artificial backdoor subsidy for the bolt industry. Anyway, I've ordered the cheap Bergen one, hopefully that will do the job. Thanks chaps.
Applying torque to fixings is not just the case of setting a torque wrench and away you go, lots of things need to be considered for example, the amount of thread that is working on the bolt, the material of the threads either of the bolt or the material it is going into, is there lubricant on the threads, is a washer being used, what type is it or material its made from.
As Burnerman has mentioned, applying the degree method most of the above does not have to be considered if using new fixings because it has all been calculated into the yield of the bolt.
Most people have problems when applying torque as recommended in the manual because the torque figures given are for a new build with the correct fixings and threads that have not been either pre-stressed or over stressed or even lubricated. How many of us have taken off a cylinder head and had oil run down into the fixing holes and rebuild without washing the oil out. A torque value is calculated to overcome friction, stretch the fixings material, to apply a certain load on the interface to name a few criteria.
As Burnerman has mentioned, applying the degree method most of the above does not have to be considered if using new fixings because it has all been calculated into the yield of the bolt.
Most people have problems when applying torque as recommended in the manual because the torque figures given are for a new build with the correct fixings and threads that have not been either pre-stressed or over stressed or even lubricated. How many of us have taken off a cylinder head and had oil run down into the fixing holes and rebuild without washing the oil out. A torque value is calculated to overcome friction, stretch the fixings material, to apply a certain load on the interface to name a few criteria.
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I'd say there's an equation for it, somewhere?
Since the late 1980s, head bolt design has changed, and we now torque down the head bolts to the point that they yield into their plastic range, rather than just sitting in their elastic range as previously.
Once in the plastic range, changing the strain doesn't have much impact on the stress exerted in the bolt, which likewise means that the clamping force isn't greatly altered. By tightening down to an angle, not a torque, you are ensuring that the bolt has yielded into the plastic range and is at the correct strain as specified by the manufacturers.
Using these types of head bolts does mean that they likely need replacing when you remove them, as you risk straining the bolt too far when you re-install, and them snapping. The major benefit is they stop car manufacturers from having to call each car in at 1000 miles to re-torque the head bolts, which would involve some considerable work on today's engines.
You beat me to it! Yes, that's exactly it. Torque-to-yield bolts exploit an unusual property in steel, which most other materials don't exhibit. Once it has yielded, you can turn it quite a long way without the clamping force changing very much. That's the place the manufacturers wants to be.
It's not just about re-torquing after 1000 miles (I think that was more to do with the gasket material relaxing), but getting an even clamping load on the joint. As has been said, the problem with trying to measure clamping load from torque, is that you have to assume that all the resistance the torque wrench is overcoming, is actually translated into clamping force. Obviously, if you have one, perfectly-lubricated bolt (both in the threads and under the head / washer) and do it up to a torque of "x" you get a clamping force of "y". If you apply the same torque to one with a bit of swarf down the thread, or less lubrication, or a bit of something under the head, you'll get a smaller clamping force. With torque-to-yield, the tightening torque is a relatively low one, to get the bolt "seated" and then the tightening is done on angle (which (assuming the pitch of the bolt thread is the same on all of them) is much more accurate. Also, once the bolt has yielded, the torque won't change much as the angle changes, so it's not accurate enough doing it on torque alone - there would be too much danger of snapping some of the bolts.
It's not just about re-torquing after 1000 miles (I think that was more to do with the gasket material relaxing), but getting an even clamping load on the joint. As has been said, the problem with trying to measure clamping load from torque, is that you have to assume that all the resistance the torque wrench is overcoming, is actually translated into clamping force. Obviously, if you have one, perfectly-lubricated bolt (both in the threads and under the head / washer) and do it up to a torque of "x" you get a clamping force of "y". If you apply the same torque to one with a bit of swarf down the thread, or less lubrication, or a bit of something under the head, you'll get a smaller clamping force. With torque-to-yield, the tightening torque is a relatively low one, to get the bolt "seated" and then the tightening is done on angle (which (assuming the pitch of the bolt thread is the same on all of them) is much more accurate. Also, once the bolt has yielded, the torque won't change much as the angle changes, so it's not accurate enough doing it on torque alone - there would be too much danger of snapping some of the bolts.
There certainly seemed to be a correlation from Fords of that era, and I cannot see much change in the design of gasket material taking place on what were effectively the same engines as they had before.
When the initial thermal cycling takes place, during the first 1000 miles, the gasket material relaxes slightly and the clamping force is reduced. I suspect that, as with any gasket, if the clamping force is too low, it will start leaking. This is very much likely to occur using the classic torque tightening method. By obtaining an accurate and even clamping force in the first place, however, using TTY bolts, you reduce the risk of the clamping force reducing to the point where the gasket will leak.
Unfortunately that doesn't prevent manufacturers specifying silly angles like 16 deg then 81 deg
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