Olives that aren't

[nicknorman]

53 minutes ago, WotEver said:

So I put the bolt in, torque it up, take it out and measure it? 

Err no, you need to have access to both ends of the bolts, obvs

It’s something my helicopter maintenance colleagues did for some of the more critical bolts. And of course it then makes you realise that what keeps bolt tension is (amongst other things) bolt stretch. Especially if you have dissimilar materials with different thermal expansion coefficients. In such cases it can be better to have a thinner bolt that stretches more, thus keeping things in tension even under adverse thermal expansions, rather than a thicker bolt that doesn’t stretch much under the required tightness force and thus could completely release is tightness under adverse thermal conditions.

Edited November 27, 2017 by nicknorman

[RLWP]

59 minutes ago, WotEver said:

So I put the bolt in, torque it up, take it out and measure it? 

It's exactly what the angular tightening does. Half a turn on a bolt with 1mm pitch extends it by 0.5mm.

Richard

[WotEver]

21 minutes ago, RLWP said:

It's exactly what the angular tightening does. Half a turn on a bolt with 1mm pitch extends it by 0.5mm.

I think I saw something like that in an Ann Summers book once...

31 minutes ago, nicknorman said:

Err no, you need to have access to both ends of the bolts, obvs

It’s something my helicopter maintenance colleagues did for some of the more critical bolts. And of course it then makes you realise that what keeps bolt tension is (amongst other things) bolt stretch. Especially if you have dissimilar materials with different thermal expansion coefficients. In such cases it can be better to have a thinner bolt that stretches more, thus keeping things in tension even under adverse thermal expansions, rather than a thicker bolt that doesn’t stretch much under the required tightness force and thus could completely release is tightness under adverse thermal conditions.

Interesting, thanks

I love mechanichy things. I miss servicing my own car (apart from the getting cold and wet bit). 

I used to help service the Stampes and Tigers at The Tiger Club in my late teens - loved it. 

[nicknorman]

46 minutes ago, RLWP said:

It's exactly what the angular tightening does. Half a turn on a bolt with 1mm pitch extends it by 0.5mm.

Richard

Not exactly. The angular method moves the bolt head in a specified amount. But it doesn’t tell you the tension on the bolt because it depends on how compressible whatever it is you are bolting up is. Measuring the bolt stretch is the gold standard - although of course it’s often unfeasible to get to both ends of the bolts with a measuring device.

Engine-wise it’s sometimes used for big end bolts, eg http://www.hotrod.com/articles/using-rod-bolt-stretch-tool/

Edited November 27, 2017 by nicknorman

[MtB]

1 hour ago, WotEver said:

So I put the bolt in, torque it up, take it out and measure it? 

 

A technique I thought up many years ago but don't generally use these days is to tighten the bolt until the thread strips, then back off an eighth of a turn.  

[WotEver]

18 minutes ago, Mike the Boilerman said:

 

A technique I thought up many years ago but don't generally use these days is to tighten the bolt until the thread strips, then back off an eighth of a turn.  

Yes, backing off would be important because you’d not want to damage anything. 

[dmr]

I thought the angle tightening thing was because the bolts are so tight that they have gone beyond their "elastic" region and are on the threshold of yield and so torque is no longer a good measure of tightness, and this is the reason why that cylinder bolts tightened in this way must be used only once. ????

Dave

[MtB]

37 minutes ago, dmr said:

I thought the angle tightening thing was because the bolts are so tight that they have gone beyond their "elastic" region and are on the threshold of yield and so torque is no longer a good measure of tightness, and this is the reason why that cylinder bolts tightened in this way must be used only once. ????

Dave

 

Hmmm this raises another thought that has swum around my mind unverbalised for decades. 

The yield threshold exists not only in tension but in torque too. I wonder sometimes if a torque yield threshold is ever approached (or exceeded) when winding up a poorly lubricated bolt to a high torque setting.

[dmr]

8 hours ago, Mike the Boilerman said:

 

Hmmm this raises another thought that has swum around my mind unverbalised for decades. 

The yield threshold exists not only in tension but in torque too. I wonder sometimes if a torque yield threshold is ever approached (or exceeded) when winding up a poorly lubricated bolt to a high torque setting.

Thinking back to my early days of car fixing, I reckon that most bolt failures where torsion failures whilst undoing rusted in bolts. I say early days because I once graduated from minis to VW campers the bolts stopped failing!   I think failures due to over-tightening are also torsion. I have lost touch with modern cylinder heads a bit of late, but   some of the early "angle tightening bolts" were narrowed between the head and top of the thread, I assume control the stretch. I expect that Richard, or some other mech engineer, will tell us that there is a simple relationship between stretch, torsional deformation, and bolt diameter.

.............Dave

[RLWP]

9 minutes ago, dmr said:

Thinking back to my early days of car fixing, I reckon that most bolt failures where torsion failures whilst undoing rusted in bolts. I say early days because I once graduated from minis to VW campers the bolts stopped failing!   I think failures due to over-tightening are also torsion. I have lost touch with modern cylinder heads a bit of late, but   some of the early "angle tightening bolts" were narrowed between the head and top of the thread, I assume control the stretch. I expect that Richard, or some other mech engineer, will tell us that there is a simple relationship between stretch, torsional deformation, and bolt diameter.

.............Dave

Yes, there is

As I said earlier, the rotation of the head directly to the extension of the bolt through the thread pitch. We can safely ignore the compressibility of the things being bolted together because of the bulk of material compared to the bolt diameter. The compressibility will be orders of magnitude smaller than the bolt stretch

The necked part of the bolt is designed to stretch and is often ground to reduce surface stresses. As long as the bolt isn't overtightened, there is a straight line relationship between the tension in the bolt and the distance it is stretched - this is basic spring stuff due to Hookes law

There is no permanent deformation either. You want the bolt to be acting as a spring

So you've got a simple relationship between the bolt head rotation, the amount of stretch in the bolt and the holding down force

Richard

Edited November 28, 2017 by RLWP

[dor]

56 minutes ago, RLWP said:

The necked part of the bolt is designed to stretch and is often ground to reduce surface stresses. As long as the bolt isn't overtightened, there is a straight line relationship between the tension in the bolt and the distance it is stretched - this is basic spring stuff due to Hookes law

There is no permanent deformation either. You want the bolt to be acting as a spring

So you've got a simple relationship between the bolt head rotation, the amount of stretch in the bolt and the holding down force

Richard

Interesting point this.  We are always told that you shouldn't re-use cylinder head bolts/studs, yet if there is no permanent deformation, and they truly do act as a spring, they should be reusable.  In my A35/mini days it wasn't unusual to have the head off an engine several times, and I never replaced the studs.

On my Vetus engine, one of the head bolts sheared and I was strongly advised to replace all the bolts. However it seems that the Vetus engines were prone to shearing head bolts as the original Mitsubishi bolts had a lower tensile strength (as indicated by the number on the top) than later ones.  I think the old ones had an '8' on them, the replacement ones a '12'.

[dmr]

1 hour ago, RLWP said:

Yes, there is

As I said earlier, the rotation of the head directly to the extension of the bolt through the thread pitch. We can safely ignore the compressibility of the things being bolted together because of the bulk of material compared to the bolt diameter. The compressibility will be orders of magnitude smaller than the bolt stretch

The necked part of the bolt is designed to stretch and is often ground to reduce surface stresses. As long as the bolt isn't overtightened, there is a straight line relationship between the tension in the bolt and the distance it is stretched - this is basic spring stuff due to Hookes law

There is no permanent deformation either. You want the bolt to be acting as a spring

So you've got a simple relationship between the bolt head rotation, the amount of stretch in the bolt and the holding down force

Richard

Have a look at TTY bolts in Google, I was right, some bolts are indeed tightened past their elastic limit which explains the angle tightening thing and the use only once.

Scary stuff and appears most common with modern engines and Ali heads so not likely to cause worry to proper boat engines like your Listers. I do note that my JD3, even with an iron head, has "use once" head bolts so sleepless nights for me worrying about this.

Modern automotive engineering does some very worrying things in the name of progress. I believe some con rods are made in one piece and then the bottom deliberately broken off to fit the shells.

...............Dave

[bizzard]

32 minutes ago, dor said:

Interesting point this.  We are always told that you shouldn't re-use cylinder head bolts/studs, yet if there is no permanent deformation, and they truly do act as a spring, they should be reusable.  In my A35/mini days it wasn't unusual to have the head off an engine several times, and I never replaced the studs.

On my Vetus engine, one of the head bolts sheared and I was strongly advised to replace all the bolts. However it seems that the Vetus engines were prone to shearing head bolts as the original Mitsubishi bolts had a lower tensile strength (as indicated by the number on the top) than later ones.  I think the old ones had an '8' on them, the replacement ones a '12'.

The thing is you don't want to stretch or torque them more than once. Each time they're used again they get weaker, they're tightened to their elastic limit as it is.  A bit like keep bending a bit of metal back and forth between the fingers, it  gets weaker and weaker with stretch and eventually snaps, especially when cold.  With the stud and nut head fastenings the nuts thread distorts slightly to apply the slight stretch being not as hard as the high tensile stud. The nuts should be renewed sfter one use, although we very  often didn't.  The use of washers is another which has largely been eliminatede on high stress things like head bolts by useing a larger pressure area under the head  of the bolt and being accurately machined matching an accurately machined area around the heads bolt holes. Eliminating washers also reduces any tendancy for the bolts to come undone having only one contact area instead of two. Ford was one of the first engine makers to eliminate washers on high stress fittings.

[MtB]

1 hour ago, dor said:

Interesting point this.  We are always told that you shouldn't re-use cylinder head bolts/studs, yet if there is no permanent deformation, and they truly do act as a spring, they should be reusable.  In my A35/mini days it wasn't unusual to have the head off an engine several times, and I never replaced the studs.

On my Vetus engine, one of the head bolts sheared and I was strongly advised to replace all the bolts. However it seems that the Vetus engines were prone to shearing head bolts as the original Mitsubishi bolts had a lower tensile strength (as indicated by the number on the top) than later ones.  I think the old ones had an '8' on them, the replacement ones a '12'.

 

Point of order here.

Did you head bolt really shear, or did it snap? Shear force is the sideways 'cutting' force, such as applied to material by a guillotine of pair of scissors for example. There is torsional 'shear' component to bolt rusted in as Dave mentioned earlier. Did you head bolt break spontaneously or during removal?

 

[bizzard]

Way back in 1956 the Mk2 Ford Consul engine of 1703cc and then the 6 cyl engines too had hefty head bolts using washers, but of not the modern stretch type, their head gaskets were of thinish sheet shim steel , embossed around the cylinder, water and oli holes, they worked well and rarely blew the gasket, quite accurate engineering I'd say. Other vehicle engine makers used the same, the old 6 cyl twin cam Jaguar engines too which used studs and nuts to hold the head on. The 3500 Rover V8 was the same, but used bolts., As did the old 6 cyl Aston Martin Lagonda engine for example.  All the early BMC's used copper asbestos gaskets, studs and nuts, more recent ones used the sticky Halilite type of gasket along with many other manufacturers.

[dor]

6 minutes ago, Mike the Boilerman said:

 

Point of order here.

Did you head bolt really shear, or did it snap? Shear force is the sideways 'cutting' force, such as applied to material by a guillotine of pair of scissors for example. There is torsional 'shear' component to bolt rusted in as Dave mentioned earlier. Did you head bolt break spontaneously or during removal?

 

It broke of its own accord.   I was looking at the engine and saw a hole where a bolt head should be.  I found the bolt under the engine; it had sheared about halfway along.

I took the head off to be able to get to the remains of the bolt which was about half an inch proud of the block.  It was barely finger-tight, so much so that I suspect if I had realised how easy it was to turn I could probably have extracted it with a magnet without having to take the head off.

ETA: I used the term "sheared" through common usage - you are quite right that technically it didn't shear.

Edited November 28, 2017 by dor

[Stephen Jeavons]

Methinks you guys need to fire up a separate post about tightening bolts.

My OP about olives is clearly a distant memory. It's been interesting though

[bizzard]

Olive Oyle had elastic stretch legs. Bluto when he kidnapped her sometimes tied knots in them to stop her escaping.

[Jen-in-Wellies]

28 minutes ago, Stephen Jeavons said:

Methinks you guys need to fire up a separate post about tightening bolts.

My OP about olives is clearly a distant memory. It's been interesting though

If you heat up a 22mm compression olive then the words

Ash nazg durbatulûk, ash nazg gimbatul, ash nazg thrakatulûk, agh burzum-ishi krimpatul

appear. Well known fact.

Jen

 

[jonesthenuke]

On 11/27/2017 at 13:13, Mike the Boilerman said:

 

They haven't changed. They've been like that in proper "Wade" brand fittings for as long as I can remember. Nor does the thread almost strip when tightening them.

Are you a competent LPG installer? It doesn't sound like it.

Wade may be traditional and will work if assembled correctly but I would not call them "proper". For that I would use Swagelok or an equivalent, though you won't like the price!

[jonesthenuke]

18 hours ago, nicknorman said:

Not exactly. The angular method moves the bolt head in a specified amount. But it doesn’t tell you the tension on the bolt because it depends on how compressible whatever it is you are bolting up is. Measuring the bolt stretch is the gold standard - although of course it’s often unfeasible to get to both ends of the bolts with a measuring device.

Engine-wise it’s sometimes used for big end bolts, eg http://www.hotrod.com/articles/using-rod-bolt-stretch-tool/

For big bolts where you want to measure stretch a standard method is to drill a small hole down the center for most of the length. You can then use a depth guage to measure the stretch from one end.  Same sort of idea with heated bolts. Drill hole down the centre to insert a heater. Tighten the nuts to remove all slack when cold. Heat the bolt to make it expand, tighten the nuts again to remove the slack and allow the bolt to cool. The temperature the bolt is heated to defines the stretch and consequent force in the fastener. Te advantage is that you do not need to apply huge torque.

Apologies that this is going off the thread, its hardly the technology required for a narrow boat!

[jake_crew]

4 hours ago, Jen-in-Wellies said:

Ash nazg durbatulûk, ash nazg gimbatul, ash nazg thrakatulûk, agh burzum-ishi krimpatul

Interesting, 40+ years since I last heard it, I recognised that quote straight away !

Edited November 28, 2017 by jake_crew
spleling

[Chewbacka]

3 hours ago, jonesthenuke said:

For big bolts where you want to measure stretch a standard method is to drill a small hole down the center for most of the length. You can then use a depth guage to measure the stretch from one end.  Same sort of idea with heated bolts. Drill hole down the centre to insert a heater. Tighten the nuts to remove all slack when cold. Heat the bolt to make it expand, tighten the nuts again to remove the slack and allow the bolt to cool. The temperature the bolt is heated to defines the stretch and consequent force in the fastener. Te advantage is that you do not need to apply huge torque.

Apologies that this is going off the thread, its hardly the technology required for a narrow boat!

There was a company that made washers with dimples/bumps on the mating surface that would progressively collapse as the clamp load increased.  When the washer was flat the clamp load/bolt tension was correct.  Not sure if you can get them any more.  

[David Mack]

1 hour ago, Chewbacka said:

There was a company that made washers with dimples/bumps on the mating surface that would progressively collapse as the clamp load increased.  When the washer was flat the clamp load/bolt tension was correct.  Not sure if you can get them any more.  

Google " load indicating washers".