Torque wrenches/leverage.

[Wallace]

HI,
2 questions, one short one long; I recently did a TB replacement on my TDI PD and found that getting everything apart wasn't too bad but fitting a big Torque wrench into confined spaces to get it all back together was quiet difficult. Also despite purchasing a fairly good wrench I have found that some of the VW values are so low that they are off the scale. So my first question is; are there smaller wrenches around or at least ones that have values at the lower end of the scale?
My second question is concerning leverage and Torque wrenches. I had to do the top mount bearings on my wife's car a couple of months ago, couldn't use the Torque wrench to re-tighten them as you need to hold the centre rod with an allen key, didn't think it was really that important, value is; Stage 1. 60nm, Stage 2. 90 degrees more (per Haynes manual), which is pretty tight if you ask me, so what I did was I tightened them just using a swan neck spanner as best I could . I have discovered since there is a tool called a Crows foot spanner for doing the job but I haven't managed to track one down yet. It's like the head of an open ended spanner with a small bit of the shank at the back and square section hole in it that can take a ratchet/Torque wrench (picture only seen on net). So guess what we broke a bearing last week , one of the new ones, so when I replaced it I thought I better get the Torquing thing right this time. No-one in my immediate area seems to do mechanics tools anymore so I came up with a couple of ideas as to what I could do, the strut top nut is 21mm which is the same as a plug spanner and gives you the extra height you need to clear the mounting plate, it also has a hex section at the top so can be gripped with a spanner, so I thought if I could fit somthing into the other end of the spanner that would take a square section I could use the Torque wrench on there.
Tried it today but it didn't work , Torque wrench was never going to click out and I think the reason is the extra leverage caused by the extra length of the spanner between the nut and wrench. If this is the case though then the Crows foot must suffer from the same difficulty. Having never seen one I don't know if they maybe come with instructions to reduce manufacturers values by a certain amount due to the length of the tool or even if it is possible to calculate a value to reduce the setting by X amount from the additional length....or am I talking crap?
Sorry this is so long but I would appreciate people's views on this, I didn't do any of this stuff at school and I am pretty much self taught a far as mechanics goes so I am learning all the time.
Thanks .
Wallace.

 

[Curious Chris]

What is the range on your torque wrench? I have nice SnapOn 3/8" drive that goes to hmmm 100 ft-lbs and is very compact.

Oh the crow foot is very available in the Etats-Unis. Or check out this Ebay link: http://cgi.ebay.com/16-PC-SAE-METRI...ryZ20773QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


For low end torque readings you want a lower range wrench so it will be accurate on the low end; or better put you are in the middle 50% of the wrench when you are using it. And when you use a crow foot you will want to lower it based on the centerline of the crow foot as you are making a class 1 lever that is multiplying the force.

 

[Wallace]

HI, Thanks for the reply, not sure I understand it 100% though, correct me if I am wrong. Basically I am right that the value would need to be reduced but I am not sure how I would do that based on what you say. Got the Torque wrench bit OK, I think I will need to acst the Snap on man when he is down at my local garage, already considered this anyway. I would need to check my current wrench to tell you the range acurately, will do this in the next couple of days though, thanks again.

 

[VW Vet]

Wallace,

I used a spark plug socket, allen wrench, and crows foot as you described. It worked well.
When using crows foot on a torque wrench, the correction factor is minimal. However, if you set the crows foot at a 90 degree angle to the torque wrench, the correction factor is zero.

 

[Wallace]

HI, I really should have the Crows foot I know and I think I am getting my head round the leverage thing which does make sense to me about the 90 degree thing. Say for example though I was going to do what i suggested with a normal spanner, is it possible to calculate a reduction or would I need a BA in Mathematics?

 

[DERV-NERD]

Your first question: You need a torque wrench that is 0 to 30nm's.

They go up in different sizes.
The next is 30 to 210Nm's and so on.

In the uk anyway.

 

[VW Vet]

Wallace,

Even if you use a spanner which is longer than a regular crows foot, setting it at 90 degrees to the torque wrench gives you a zero correction factor.

Edit to add: go here, http://www.motionpro.com/images/documents/08-0134.pdf to see the formula you need. It is on page 2 of the pdf.

 

[Wallace]

Thanks guys, my current Torque wrench starts at 30nm so I need the one below that, hopefully it will also be of smaller dimensions. Somtimes you just need someone to bounce ideas off and I have always found you guys to be great, Cheers.

 

[DERV-NERD]

Thanks guys, my current Torque wrench starts at 30nm so I need the one below that, hopefully it will also be of smaller dimensions.

It is.

 

[Curious Chris]

Well the second page of the pdf confirmed my hypothesis: when you put a lever arm on the end of the torque wrench you are increasing the applied torque! Oh you have to rotate farther but the torque is increased. Think about a wheel barrow.

 

[Powder Hound]

For those fine values, sometimes you just need to find one that is graduated in that scale. Or, possibly a smaller drive. That is, a 1/4" drive or one that is calibrated in inch-pounds instead of foot-pounds. Or if all you find is metric/ newton-meter stuff, then look for the range.

Another really important note is that many such wrenches are badly calibrated as you buy them. I tried one I just purchased and I think the torque values were double the scale.

 

[Curious Chris]

Ebay has great Snap On wrenches. I checked mine at work and it was spot on.

 

[DERV-NERD]

Another really important note is that many such wrenches are badly calibrated as you buy them.

Due to people not unwinding them after use!

Leaving a torque wrench set at 50nm's lets say, and putting it away like this for a month or so weakens the internals, which inturn alters the calibration.

 

[DanG144]

I would not go with using a crow's foot at 90 degrees. Use it straight out instead. A link to a calculator is below.

http://www.norbar.com/torquewrenchextensioncalculator.php

This would work for a crows foot or any other exterder.

I was taught that when you could not get the torque wrench into place that you should simply tighten another (non critical) bolt with the torque wrench, then use the same wrench you must use on the real bolt to get the feel for how much torque it takes to cause movement. If you are in an awkward position for the real bolt, try to duplicate the awkward position for the practice. This really works pretty well. Good enough for the nuclear navy.

Dan

 

[Lug_Nut]

The "90 degree means zero conversion adjustment" is false. The offset adjustment is by the amount of the hypotenuse over the length of the wrench alone.
A foot long wrench with a foot long (absurd) crow's foot adapter mounted 90 degrees to the torque wrench would put the nut at 1.414 feet from the wrench handle and would then need the inverse (.707) factor to the setting.

 

[VW Vet]

The "90 degree means zero conversion adjustment" is false. The offset adjustment is by the amount of the hypotenuse over the length of the wrench alone.
A foot long wrench with a foot long (absurd) crow's foot adapter mounted 90 degrees to the torque wrench would put the nut at 1.414 feet from the wrench handle and would then need the inverse (.707) factor to the setting.

You are wrong, sir.
The hypotenuse does not figure into it.
If the crows foot is positioned straight in front of the torque wrench, you would adjust your wrench to a lower value.
If the crows foot is positioned 180 degrees from that, you would adjust your wrench to a higher value.
At the 90 degree point, you would pass the correction factor of ZERO.
Go to this site http://www.motionpro.com/images/documents/08-0134.pdf and read what it says on page 2 about 90 degrees.
Edit to add: Go here http://www.engineersedge.com/manufacturing_spec/torque_wrench_2.htm to see an example of a "minus" calculation.
Also, every Air Force Technical Order I have used over the last 35 years has agreed with this. They even include diagrams showing the extension as a "plus" and a "minus". At 90 degrees it is neither plus nor minus!
Please, no arguing over this.
Edit again to add: http://home.jtan.com/~joe/KIAT/kiat_3.htm scroll down to the 90 degree figure.
And: http://www.trialsnuts.com/TORQUED.pdf see page 2 to see the effective length of an adapter at an angle.

 

[VW Vet]

To simplify using an extension on a torque wrench, there is no need to figure a correction if arranged as pictured:

 

[BugBug]

You are wrong, sir.
The hypotenuse does not figure into it.
If the crows foot is positioned straight in front of the torque wrench, you would adjust your wrench to a lower value.
If the crows foot is positioned 180 degrees from that, you would adjust your wrench to a higher value.
At the 90 degree point, you would pass the correction factor of ZERO.
Go to this site http://www.motionpro.com/images/documents/08-0134.pdf and read what it says on page 2 about 90 degrees.
Edit to add: Go here http://www.engineersedge.com/manufacturing_spec/torque_wrench_2.htm to see an example of a "minus" calculation.
Also, every Air Force Technical Order I have used over the last 35 years has agreed with this. They even include diagrams showing the extension as a "plus" and a "minus". At 90 degrees it is neither plus nor minus!
Please, no arguing over this.
Edit again to add: http://home.jtan.com/~joe/KIAT/kiat_3.htm scroll down to the 90 degree figure.
And: http://www.trialsnuts.com/TORQUED.pdf see page 2 to see the effective length of an adapter at an angle.

Verry well stated.
This may be a well known fact (or not):

• Never use a torque wrench to remove a bolt or tighten a left handed thread bolt, unless it is designed for bi-directional torque.
• Before putting the wrench away, reset it to zero.

The Auto Zone store here has a good selection of torque wrenches. 1/4", 3/8" and 1/2" with scales in lb/ft and nm. These are for right hand threads only. Snap-on has a couple special order torque wrenches that are bi-directional.
For conversion from metric to standard, go here.
Hope this helps.

EDIT: Question to VW VET. Would your calculation for torque2 still be acurate if the extension/wrench is longer than the torque wrench?

 

[DrSmile]

You guys are scary...

The only time I use a torque wrench is when I'm rebuilding a motor. Everything else is just finger tight, tight, or as tight as I dare... Once you wrench a while you trust your wrist a lot more than a silly torque wrench.

 

[BugBug]

DrSmile,

That silly torque wrench can keep things from falling off or worse yet breaking off if used correctly. Some experienced mechanics may be able to get away with your method 99 out of a 100 times. However, when you tighten a critical bolt, like one that holds your motor up or a glow plug in an aluminum head. You may want to think twice about your methods. Rework is at the least twice as expensive as the original job, plus additional parts.
Just trying to help ;-)

 

[DrSmile]

I readily admit I break and strip bolts and threads... but anyone who works on cars will, especially in the rustbelt where I am. Unless you chase EVERY thread, nut, and bolt before you assemble them the given torque specs are meaningless. Iron corrodes, aluminum corrodes, even stainless steel does. Even if it didn't, dirt will get in the threads and throw off the specs. Working on cars isn't like working in a clean room. I have a whole drawer full of lefty drills, extractors, stud and screw pullers, nut busters, taps, dies, and a lovely collection of helicoil kits. It's part of the job to need and use them.

 

[VW Vet]

BugBug,
Interesting question you have posed.
Using the formula to figure the torque for an extension, as soon as the effective length of the extension in the negative range is bigger than the torque wrench length, you would be loosening the nut. The point of pull (your hand) would be on the wrong side of the nut, applying a left turn to it. The answer to the calculation is a negative torque.
A standard, very short crows foot need not be calculated.

 

[lost1wing]

Before putting the wrench away, reset it to zero

I have a snap-on and a no name torque wrench and both instructions say to back off torque setting to a low setting but not zero. I guess you have to decide for yourself to follow printed instructions for your torque wrench or do it the way you were told.

 

[mechanicalbrew]

seems that it has already been answered, but if you keep the extension perpendicuar to the shaft of the torque wrench (as pictured above) it would be the same amount of torque (zero correction) at the nut. I am an engineering student and just got done taking statics. we did this exact same problem for homework. it may seem counter-intuitive, but it is correct.

the techicnical explanation is that when you are calculating a moment (torque), the x distance is multiplied by the force in the y direction (and the same the other way around) here you are taking a force in the y direction and moving it a distance in the y direction. the new distance would only come in to play if there was a force in the x-direction (which there is not)

Just in case anybody cares

 

[Lug_Nut]

(Easier to quote the drawing than to describe my point)
The force being applied to the wrench handle above is NOT radial to the fastener. Lengthening the extension exacerbates this angular application of force. A theoretical infinitely long extension will have the force applied to the wrench head actually applying no torque to the fastener, but only attempting to sheer it off. With that imaginary infinite length extension it will be necessary to apply force 90 degrees to the direction shown in the drawing, pulling the handle away from or towards the ratchet head, to actually apply torque to the fastener. Torque will be applied to the fastener although none is applied at the wrench head.
An extension of length EQUAL to the length of the wrench will require applying force at a 45 degree angle to the arrow as shown above to apply all the force onto the fastener. The amount of torque needed at the ratchet head to produce some torque at the fastener WILL be a factor based on the angle of the wrench to extension and the lengths of each.
As the ratio of wrench length to extension length increases (shorter extension), the difference between head torque and fastener torque become closer to equal. With a short extension it will be close enough that the inherent wrench inaccuracy become greater than the angular factor.

 

[BugBug]

(Easier to quote the drawing than to describe my point)
The force being applied to the wrench handle above is NOT radial to the fastener. Lengthening the extension exacerbates this angular application of force. A theoretical infinitely long extension will have the force applied to the wrench head actually applying no torque to the fastener, but only attempting to sheer it off. With that imaginary infinite length extension it will be necessary to apply force 90 degrees to the direction shown in the drawing, pulling the handle away from or towards the ratchet head, to actually apply torque to the fastener. Torque will be applied to the fastener although none is applied at the wrench head.
An extension of length EQUAL to the length of the wrench will require applying force at a 45 degree angle to the arrow as shown above to apply all the force onto the fastener. The amount of torque needed at the ratchet head to produce some torque at the fastener WILL be a factor based on the angle of the wrench to extension and the lengths of each.
As the ratio of wrench length to extension length increases (shorter extension), the difference between head torque and fastener torque become closer to equal. With a short extension it will be close enough that the inherent wrench inaccuracy become greater than the angular factor.

Good answer. That makes sense. Thank you.

 

[Lug_Nut]

the techicnical explanation is that when you are calculating a moment (torque), the x distance is multiplied by the force in the y direction (and the same the other way around) here you are taking a force in the y direction and moving it a distance in the y direction. the new distance would only come in to play if there was a force in the x-direction (which there is not)

Just in case anybody cares

Caught why you're wrong!
There IS displacement in the X direction. The pivot is about the fastener, not about the wrench head.
There is mostly motion in the Y+, but there is a motion in the X- also.
The further the fastener is from the handle because of lengthened extension, the more X- there will be relative to the Y+ motion. A very short extension will have little X-.

 

[mechanicalbrew]

right but there is no force in the x direction. and every time the bolt moves, the extension is still perpendicuar to the torque wrench. unless there is significant flex (some way that it would not be 90deg), the moment (torque) does not change. i could be wrong, but i would stand by torque 1=torque 2.

anyone else out there care to offer their assesment? i will look for the proof for those who want a definitave answer

 

[VW Vet]

right but there is no force in the x direction. and every time the bolt moves, the extension is still perpendicuar to the torque wrench. unless there is significant flex (some way that it would not be 90deg), the moment (torque) does not change. i could be wrong, but i would stand by torque 1=torque 2.

anyone else out there care to offer their assesment? i will look for the proof for those who want a definitave answer

All the proof needed has been presented earlier in this thread (including the part about the 90 degree angle arrangement being true).
In the practical world, (as opposed to the theoretical world with an infinately long extension ), with tools one actually has in the tool box, all one needs to know is the formula for recalculating torque works, and is accepted in the automotive and aviation industries. I don't know what else it would take to convince the naysayers. Unfortunately, those who don't know whom to believe are left not knowing what to do when they need to add an extension to their torque wrench.

 

[lost1wing]

After reading this thread, I got confused about what I thought to be the correct way to read a torque wrench with a crows foot. So I went to my tool room at work. I took a torque wrench and a crows foot to the certified calibration tool. The torque set on the wrench was 40 inch lbs The torque wrench was verified at 38.8 inch pounds (avg of five checks). Without moving my hand from the torque wrench, I installed the crows foot adapter at a 90 degree angle. Note that the crows foot length was 7/8 inch center to center. When the torque wrench clicked (still set at 40 inch lbs) the meter showed 39.2 inch pounds (avg of 5 checks).

My conclusion: No correction needed with this length crows foot. If a longer crows foot, say 2 inches was used, I would say a correction may be needed. I would definitely check in to it.

Edit was to put my numbers in the right place.