| [ Total Views: 824 | Total Replies: 21 | Thread Id: 96811 ] |
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 donn
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| posted on May 9th, 2012 at 09:36 AM |
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Realy dumbo question re tension wrench
So I'm refitting the preasure plate to the flywheel, the book says 2.5kg/m or 18 ft/lb
My tension wrench dosn't have kg/m it has newton meters (same thing ?)  or ft/lbs so I'm using that but it only has markings down to 22.1 ft/lbs, so I set it a little below that however I need to put
a hell of a lot of preasure on it and it still dosn't register, I'm thinking that the t/wrench is stuffed  but to check it I set it back at 88.5 ft/lb and it "clicks" it easy. Am I reading the scale wrong?
 can I just do the preasure plate bolts up tight (do they realy
need to be tensioned acuratly?)
Please answer AFTER the laughing is finished. 
Thanks
Don
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bajachris88
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| posted on May 9th, 2012 at 10:08 AM |
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there are 10 newtons of force in a kg.
If you wanna be really specific, 9.81 newtons per kg of mass given Earth's gravity at sea level lol. 
so 2.5kg/m is approx 25 newtons/metre (25 N/m)
(ô_!_/ô) (ô_!_/ô)
69' baja: kombi box, thing spindles, irs, disc front, type 3 rear drums, 2 inch lift kit, 31x10 rears.
New engine in process: 94mm p&bs, 74mm C/w chomol Crank, 35.5x39 SP heads, turbo. Wierd combo, hopeful torque monsta! |
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modulus
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| posted on May 9th, 2012 at 10:57 AM |
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| Quote: | Originally
posted by donn
can I just do the preasure plate bolts up tight (do they realy need to be tensioned acuratly?)
Don
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It's not easy to get the tension even by hand, especially as 2.5 kg m is not much at all, so it is by far best to use a torque wrench within its
calibrated range. An adequate quality torque wrench will cost less than pulling the engine again to prematurely replace the clutch.
Specifics:
1)
1 newton metre = 0.7375621 pound-foot (often "foot-pound")
1 kilogram-force metre = 9.80665 Nm[4][5]
1 pound-foot (often "foot-pound") = 1 pound force foot ≈ 1.3558 Nm
1 inch ounce-force = 7.0615518 mNm
1 dyne centimetre = 10−7 Nm
2)
Note that the units are Newton metres or foot pounds (or Newton-metres or pound-feet etc.) *not* newtons/metre or ft/lb i.e. it is not ft per pound or
Newtons per metre etc. The unit in SI measurements (Australia's standard) is the Newton-metre. Furthermore Mr. Newton did enough for physics to
deserve his leading capital letter.
3)
The threads should be clean and well oiled to get accurate results; if memory serves, Dangerous Dave has written here previously on the large
variances caused by lack of lubrication.
hth
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donn
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| posted on May 9th, 2012 at 01:40 PM |
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Ok, as usual some good advise there, and I now know why it takes less force to "click" the t/wrench at the 22 mark than the 88 mark, on this
t/wrench once the tension is set lower than the last mark then it no longer operates as a t/wrench, so that bit is solved. The book says to set the
bolts at 2.5 kg/m, so close enough to 25 Newton-metres as noted by bajachris88, my t/wrench only goes down to 30 Newton-metres (3.06 kg/m) would that
be close enough.
Yours in paranoia
Don
Oh. and my apologies to Mr. Newton, in my bewilderment I had forgotten that "Newton" was a persons name, high school was a long time ago  , rest assured that I will not forget again , and the point about cleaning and lubricating the thread and the lbs/ft
are also noted.
Thanks
Don
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modulus
A.k.a.: Peter Hill
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| posted on May 9th, 2012 at 02:46 PM |
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| Quote: | Originally
posted by donn
my t/wrench only goes down to 30 Newton-metres (3.06 kg/m) would that be close enough.
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Certainly far better than tightening by guess.
hth
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donn
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| posted on May 9th, 2012 at 02:57 PM |
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So at 30 Newton-metres I reckon I could tighten them tighter by finger, just dosn't seem tight enough, maybe I should stick to being a chipie 
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modulus
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| posted on May 9th, 2012 at 03:29 PM |
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| Quote: | Originally
posted by donn
So at 30 Newton-metres I reckon I could tighten them tighter by finger
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Yep, that's about right.
hth
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Lucky Phil
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| posted on May 11th, 2012 at 01:35 PM |
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Theoretically, all bolts should be tightened with a tension wrench, but how tedious is that?
Most people simply use the tension wrench for critical stuff like head studs etc.
On VW's, however, a lot of tensions are much less than other makes.
So I use a tension wrench a lot more when working on them.
One day, when fitting an aircon to a new mitsubishi, I checked all bolts with a tension wrench after tightening by feel out of curiosity.
The destructions had all the bolt tensions in it and all but one (the 4 compressor bolts) were within spec.
Also be aware that tension wrenches can go out of whack and should be checked periodically.
The ones that go click have an internal spring and should be completely set to zero when you finish with them.
Store them with pressure on the spring and it will change the reading.
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donn
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| posted on May 11th, 2012 at 08:46 PM |
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Thanks Phil, I'm doing a few other things B4 I put the motor back in so it's still hanging in mid air, I'm thinking I might bump the tension up a
bit as it just dosn't seem tight enough, surely a bit tighter can't hurt,(I hope)
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68AutoBug
A.k.a.: Lee Noonan
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| posted on May 11th, 2012 at 11:54 PM |
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Hi Donn
first , there are NO dumbo questions...
We all had to learn sometime... and most of Us are still learning.
I probably would have just used a socket and breaker bar Donn
and done it nice and tight...
which isn't as tight as using a big long tension wrench..
another way is to cut a spanner in half.. and use your left hand
only joking.. as I do have a couple of half spanners but they are used where the longer one wouldn't fit..
I've only got a big long torque wrench too.. lol
LEE
- [size=4]Helping keep Air Cooled VWs on the road - location: SCONE in the Upper Hunter Valley - Northern NSW 320 kms NNW of SYDNEY--- [/size]
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68AutoBug
A.k.a.: Lee Noonan
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| posted on May 11th, 2012 at 11:58 PM |
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| Quote: | Originally
posted by Lucky Phil
Theoretically, all bolts should be tightened with a tension wrench, but how tedious is that?
Most people simply use the tension wrench for critical stuff like head studs etc.
On VW's, however, a lot of tensions are much less than other makes.
So I use a tension wrench a lot more when working on them.
Also be aware that tension wrenches can go out of whack and should be checked periodically.
The ones that go click have an internal spring and should be completely set to zero when you finish with them.
Store them with pressure on the spring and it will change the reading.
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I have one that clicks the pin Phil...
it was retensioned or whatever just before I got it and its not used Much.. My Son uses it more than Me..
Can You tell me whether its OK to use the tension wrench to undo bolts???
I told My Son Not to use it that way , as its not designed to be used that way.. and I thought it would throw it out doing it backwards..??
Lee
- [size=4]Helping keep Air Cooled VWs on the road - location: SCONE in the Upper Hunter Valley - Northern NSW 320 kms NNW of SYDNEY--- [/size]
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homer
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| posted on May 12th, 2012 at 07:17 AM |
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Hi Lee.
Unless it is a ratcheting torque wrench do not use it in the reverse direction at all. Even the ratcheting wrenches are designed to tighten left hand
threads. I calibrate torque wrenches as part of my job and have seen some wrenches in a bad way after being used the wrong way.
Cheers
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cam070
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| posted on May 12th, 2012 at 07:27 AM |
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You should buy a small torque wrench. I recently ordered a 3/8 inch from amazon.com and had it delivered for less than $30.
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modulus
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| posted on May 12th, 2012 at 09:26 AM |
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| Quote: | Originally
posted by donn
... it just dosn't seem tight enough, surely a bit tighter can't hurt,(I hope)
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Yes it can. The recommended torque settings aim at stretching the metal in the screw but keeping that stretch in the elastic zone for that metal. If
you overtighten, even though you don't reach breaking point, you can move into the plastic zone where the screw's metal is permanently stretched.
The result is that, rather than "snugging it up a bit more securely", you actually *reduce* the longitudinal force between the screws threads and
the female screw's threads; the screw is more likely to become loose. But, in the end, it's your clutch, your time, your responsibility.
hth, but starting to doubt it.
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donn
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| posted on May 12th, 2012 at 05:58 PM |
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Cool, thanks modulus, so I think I'll get a new (smaller) tension wrench and do a double check, I havn't gone any further with it, maybe it would be
a good idea to get new bolts, whatcha reckon / advise.
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volumex
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| posted on May 12th, 2012 at 07:57 PM |
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I've had to do a bit of research into bolt design, and it was fascinating. Short answer is torque is a very poor way to measure bolt force. We
tested the bolts on a DN750 flange, and to get identical bolt force, the torque varied from 170 Nm to 540 Nm. IIRC about 80% of the torque goes into
overcoming friction, the rest into bolt stretch.
The Ajax Fastener handbook puts the accuracy of torque wrenches at ±30%, which is a big improvement over operator feel at ±50% but still nowhere
near accurate.
I would aim to get reasonably accurate, but don't bust a foof foof valve aiming for perfection.
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waveman1500
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| posted on May 13th, 2012 at 12:10 AM |
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| Quote: | Originally
posted by volumex
I've had to do a bit of research into bolt design, and it was fascinating. Short answer is torque is a very poor way to measure bolt force. We
tested the bolts on a DN750 flange, and to get identical bolt force, the torque varied from 170 Nm to 540 Nm. IIRC about 80% of the torque goes into
overcoming friction, the rest into bolt stretch.
The Ajax Fastener handbook puts the accuracy of torque wrenches at ±30%, which is a big improvement over operator feel at ±50% but still nowhere
near accurate.
I would aim to get reasonably accurate, but don't bust a foof foof valve aiming for perfection.
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What this man says is absolutely true. All torque settings are a fairly rough estimate, so it's just silly to say that 30Nm is way too much and will
be dangerous on a bolt specced at 25Nm. Besides which, all engineering values have a tolerance on them, and I'd be willing to guess that the spec is
probably 25 +/- 5Nm, in which case 30Nm is in spec.
I don't even own a torque wrench and have done plenty of work on my car, including changing clutches, as well as engines, steering bits, brakes and
so forth. It really isn't that critical. To be honest, the wheel bolts are a far more safety-critical joint, but how many people tension their wheel
bolts/nuts up with a torque wrench every single time?
Another thing to think about, is that doing the bolts up too tight is always better than too loose. When you do the bolt up too tight, you always put
adequate clamp load into the joint, so the bolt should never fail unless it does so as you are doing it up. If you do the bolt too loosely, the
clamping load is inadequate, so in operation the two mating surfaces can separate, stretching the bolt and potentially breaking it.
I wouldn't bother with new bolts unless the old ones have damaged threads. In terms of changing bolts, the friction coefficient of the coating on
them or the surface finish can cause huge variations in clamp load for an identical torque value. When I was working in engineering at Holden, they
were having issues with torque settings of the handbrake tensioner bolts. All handbrakes were torqued to a set value with a super-accurate electric
gun. It turned out that the bolt supplier had two different batches of electroplating, one of which was a slightly different colour. The batches got
mixed up and shipped. For the exact same torque value, one colour of zinc plating produced a handbrake that was too loose, and the other was nice and
tight. This was specified and supplied as the same material, the coatings were extremely similar. That tiny change in coating type gave a big enough
difference in friction coefficient to significantly change the bolt tension which was achieved from the same torque value.
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donn
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| posted on May 13th, 2012 at 11:49 AM |
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just knew I should have stayed with being a chippie, drive a couple more nails if it dosn't seem good enough.
I dream of a day when a chicken can cross a road without being asked for it's motive!
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68AutoBug
A.k.a.: Lee Noonan
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| posted on May 13th, 2012 at 06:37 PM |
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Excellent info waveman1500 and volumex
all makes sense too...
and what about a dry bolt and a lubricated bolt??
We all know why they don't make 10mm spanners 500mm long don't We??
as You would be snapping some bolts off..lol
I usually use new 8.8 or 10.9 hi tensile bolts on My beetle..
I used zinc plated hi tensile bolts for all My mud guard bolts,,
lol with never size...
LEE
| Quote: | Originally
posted by waveman1500
| Quote: | Originally
posted by volumex
I've had to do a bit of research into bolt design, and it was fascinating. Short answer is torque is a very poor way to measure bolt force. We
tested the bolts on a DN750 flange, and to get identical bolt force, the torque varied from 170 Nm to 540 Nm. IIRC about 80% of the torque goes into
overcoming friction, the rest into bolt stretch.
The Ajax Fastener handbook puts the accuracy of torque wrenches at ±30%, which is a big improvement over operator feel at ±50% but still nowhere
near accurate.
I would aim to get reasonably accurate, but don't bust a foof foof valve aiming for perfection.
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What this man says is absolutely true. All torque settings are a fairly rough estimate, so it's just silly to say that 30Nm is way too much and will
be dangerous on a bolt specced at 25Nm. Besides which, all engineering values have a tolerance on them, and I'd be willing to guess that the spec is
probably 25 +/- 5Nm, in which case 30Nm is in spec.
I don't even own a torque wrench and have done plenty of work on my car, including changing clutches, as well as engines, steering bits, brakes and
so forth. It really isn't that critical. To be honest, the wheel bolts are a far more safety-critical joint, but how many people tension their wheel
bolts/nuts up with a torque wrench every single time?
Another thing to think about, is that doing the bolts up too tight is always better than too loose. When you do the bolt up too tight, you always put
adequate clamp load into the joint, so the bolt should never fail unless it does so as you are doing it up. If you do the bolt too loosely, the
clamping load is inadequate, so in operation the two mating surfaces can separate, stretching the bolt and potentially breaking it.
I wouldn't bother with new bolts unless the old ones have damaged threads. In terms of changing bolts, the friction coefficient of the coating on
them or the surface finish can cause huge variations in clamp load for an identical torque value. When I was working in engineering at Holden, they
were having issues with torque settings of the handbrake tensioner bolts. All handbrakes were torqued to a set value with a super-accurate electric
gun. It turned out that the bolt supplier had two different batches of electroplating, one of which was a slightly different colour. The batches got
mixed up and shipped. For the exact same torque value, one colour of zinc plating produced a handbrake that was too loose, and the other was nice and
tight. This was specified and supplied as the same material, the coatings were extremely similar. That tiny change in coating type gave a big enough
difference in friction coefficient to significantly change the bolt tension which was achieved from the same torque value.
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waveman1500
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| posted on May 13th, 2012 at 10:08 PM |
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The difference between a dry and lubricated bolt is reasonably significant as well. It's listed in engineering manuals and such. Just for example, I
quickly looked up a table of calculations on a bolt supplier's webpage. For a 3/4" bolt to be at optimum tension, they calculated a torque value of
409ft.lb dry, 450ft.lb zinc-plated and 205ft.lbs waxed/lubricated.
http://www.zerofast.com/torque.htm
As volumex said, applied torque is such a rough estimate of bolt tension that it's really only good enough to be used for non-critical applications.
For a joint where the bolt is tensioned to near it's yield point, you would use a torque+angle spec at a minimum, or ideally you would measure the
actual bolt stretch as you would on a con-rod bolt.
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 matberry
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| posted on May 14th, 2012 at 07:56 AM |
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At a gasket makers seminar in the 90's, we were told and shown, the clampforce is changed by a factor of 7 between a dry bolt and a properly
lubricated bolt at the same torque !!!!! Lube, lube, lube.......
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
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waveman1500
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| posted on May 14th, 2012 at 03:55 PM |
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Having said that though, most bolt torques in car manuals are quoted dry, so they should be tensioned dry.
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