# Do professional mechanics really do this?



## cactusfarmer (Nov 8, 2003)

I have a question for all you pro mechanics out there. Listed throughout my FSM, there are torque specs listed for every little bolt on my engine. Do professional mechanics really torque every single bolt? Sometimes I'm lucky if I can get a socket or wrench on a bolt, much less a tourque wrench. I understand torquing the important things like headbolts etc., but what about little things like your thermostat cover bolts that are a PIA to get to? Just wondering.


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## lshadoff (Nov 26, 2002)

I use a torque wrench on every bolt I can get a socket on. With an aluminum block engine, it is too easy to strip the threads out by overtightening. Of course, certain ones are critical to tighten correctly, like head bolts, rod bolts, and cam bracket bolts (which seem to snap rather easily).

Lew


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## BII (May 13, 2004)

Well, it depends. I've seen my dad work on engines (owns his own shop, has been a technician for almost 20 years), he uses a torque wrench on every engine bolt that is absolutetly critical to have to spec. The one's that don't he usually senses when it's tight enough. I guess after 20 years or wrenching you can do somethings by feel.


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## Zen31ZR (Mar 24, 2004)

Head bolt torque is very important, as is intake manifold bolt torque, and most all internal engine things  ....Otherwise, I tend to do everything else (outside the engine) by feel. Feel can get you in trouble too though, especially with bolts that have been heat stressed, like exhaust manifold bolts. They tend to break rather easily if reused or even slightly over tightened. Same thing with bolts smaller than 10 mm. And like Ish said, you don't really want to mess around on an aluminum block. Some places are impossible to fit a torque wrench into, so I usually limit the torque I can put on a small bolt by using a "shorty" wrench, or even 1/4 drive on the really small stuff.


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## Jeff (Oct 17, 2002)

I need to buy a torque wrench...but I agree with the essential engine bolts that should be spec-torqued.


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## cactusfarmer (Nov 8, 2003)

lshadoff said:


> I use a torque wrench on every bolt I can get a socket on. With an aluminum block engine, it is too easy to strip the threads out by overtightening. Of course, certain ones are critical to tighten correctly, like head bolts, rod bolts, and cam bracket bolts (which seem to snap rather easily).
> 
> Lew


When using a torque wrench does it matter if you are using an extension or a u-joint connection? And if does, how are you supposed to allow for these factors? Sometimes I wind up with some pretty strange ratchet/extension/u-joint combinations to tighten some of my bolts. I can't help but think it would effect your torque wrench reading with all the stuff hooked onto it. Of course, I'm sure there are better ways of going at bolts than I do, but sometimes, it just seem no matter what, you gotta put some pretty strange stuff together to get the bolt tight.


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## ifoam (Dec 16, 2004)

cactusfarmer said:


> When using a torque wrench does it matter if you are using an extension or a u-joint connection? And if does, how are you supposed to allow for these factors? Sometimes I wind up with some pretty strange ratchet/extension/u-joint combinations to tighten some of my bolts. I can't help but think it would effect your torque wrench reading with all the stuff hooked onto it. Of course, I'm sure there are better ways of going at bolts than I do, but sometimes, it just seem no matter what, you gotta put some pretty strange stuff together to get the bolt tight.



im more than sure extensions dont affect it, not sure about u-joints, but i doubt they do


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## cactusfarmer (Nov 8, 2003)

?Zen31ZR? said:


> Some places are impossible to fit a torque wrench into, so I usually limit the torque I can put on a small bolt by using a "shorty" wrench, or even 1/4 drive on the really small stuff.


I like that thinking. I've been looking for an excuse to buy a 1/4 drive set and a shorty set. Now I can explain to my wife why it's so important that I have those tools in my box.


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## cactusfarmer (Nov 8, 2003)

ifoam said:


> im more than sure extensions dont affect it, not sure about u-joints, but i doubt they do


Seems like back in my Army days, we had a tech-bulletin of some sort that covered allowances for extensions on torque wrenches. Of course I wasn't a mechanic and didn't actally work on vehicles (I just kept up with the parts) so I don't remember for sure. Then again, those were 52-ton tracks and not little Nissan cars so that might have had something to do with it.


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## RBI*04 (Sep 10, 2004)

i dont torque anything to spec. unless its something to do with the engine its self (like you all said before head bolts etc.) i havent use a torque wrench on any bolt on my car.


and i think youre going a little overboard if you torque down your lugnuts


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## Radioaktiv (Feb 12, 2004)

i torque my lugnuts
guess im a nerd


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## BII (May 13, 2004)

Radioaktiv said:


> i torque my lugnuts
> guess im a nerd


That's actually a great thing to do, wheel studs are a MF to replace.


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## 94econobox (Dec 1, 2004)

cactusfarmer said:


> When using a torque wrench does it matter if you are using an extension or a u-joint connection? And if does, how are you supposed to allow for these factors? Sometimes I wind up with some pretty strange ratchet/extension/u-joint combinations to tighten some of my bolts. I can't help but think it would effect your torque wrench reading with all the stuff hooked onto it. Of course, I'm sure there are better ways of going at bolts than I do, but sometimes, it just seem no matter what, you gotta put some pretty strange stuff together to get the bolt tight.


For extensions it doesn't matter. For u-joints, it won't matter either unless you're trying to make some extreme angle and it ends up binding. Where you can run into trouble is if you do anything to lengthen the wrench (i.e. use crow's feet, etc)


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## BIRM_200SX (Dec 8, 2004)

Welllll.... We're supposed to. Not many do, sadly. Fortuantely, I wasn't one of them.


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## KA24Tech (Feb 2, 2004)

I torque every drivetrain and chassis bolt to spec. I have many different torque wrenches in my tool box. It is also important to have the torque wrench calibrated periodically to insure accuracy. For critical engine fasteners like the headbolts and rod bolts, I use the torque angle method or stretch gauge with a dial indicator which is much more accurate than a digital torque wrench. ARP bolts has a good tech article on why each of these tension methods are better or worse than the others.
http://www.arp-bolts.com/pages/tech/fastener.html
I don't do the "feel" torque because after replacing your 2000th broken stud or bolt especially the M6 or M8 bolts in the car because someone before you had an "off day" or several people did, then you start to torque more fasteners as a regular practice. I always torque suspension fasteners because if one of those pieces fails it could mean an accident or worse. The wheels are an ALWAYS torque item because not only is it a way to double check your work but it saves the rotors from warpage because of uneven preload from the different torque values on each lugnut. 
It maybe "overkill" to some but it makes for a safer more reliable vehicle after it leaves the shop because the job was done properly.
An extension on either side changes the torque values. Like the extension on a torque wrench multiplies the torque because the leverage changes. The correct torque measurement is going to be with your hand on the hand grip. The torque measurement changes when a socket extension is used as well but it is decreased. Also no reliable torque value can be obtained with a u-joint because the fulcrum angles change thus it is no longer measuring with any physical constant.

Troy


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## cactusfarmer (Nov 8, 2003)

KA24Tech said:


> I torque every drivetrain and chassis bolt to spec. I have many different torque wrenches in my tool box. It is also important to have the torque wrench calibrated periodically to insure accuracy. For critical engine fasteners like the headbolts and rod bolts, I use the torque angle method or stretch gauge with a dial indicator which is much more accurate than a digital torque wrench. ARP bolts has a good tech article on why each of these tension methods are better or worse than the others.
> http://www.arp-bolts.com/pages/tech/fastener.html
> I don't do the "feel" torque because after replacing your 2000th broken stud or bolt especially the M6 or M8 bolts in the car because someone before you had an "off day" or several people did, then you start to torque more fasteners as a regular practice. I always torque suspension fasteners because if one of those pieces fails it could mean an accident or worse. The wheels are an ALWAYS torque item because not only is it a way to double check your work but it saves the rotors from warpage because of uneven preload from the different torque values on each lugnut.
> It maybe "overkill" to some but it makes for a safer more reliable vehicle after it leaves the shop because the job was done properly.
> ...



A lot of great stuff there. You're the guy I want to work on my car.


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## KA24Tech (Feb 2, 2004)

Texas is a healthy drive from Denver...

Troy


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## cactusfarmer (Nov 8, 2003)

KA24Tech said:


> Texas is a healthy drive from Denver...
> 
> Troy


Might be worth the drive for that kind of quality mechanicing. 

So, how do you determine the correct torque wrench when you add an extension?


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## S14240SR (Aug 20, 2004)

Radioaktiv said:


> i torque my lugnuts
> guess im a nerd


I heard that torquing lugnuts incorectly can cause rotors to warp during track use


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## KA24Tech (Feb 2, 2004)

S14240SR said:


> I heard that torquing lugnuts incorectly can cause rotors to warp during track use


It can cause rotors to warp during regular street use too.

Troy


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## KA24Tech (Feb 2, 2004)

cactusfarmer said:


> So, how do you determine the correct torque wrench when you add an extension?


On the socket side if you add an extension, the forces applied to the wrench have two different directions horizontally (the direction you are pulling with the hand grip) and vertically (changing with the distance from the fastener). If you can stabilize the extension so that the the socket end of the torque wrench movement is minimumalized then most of the torque applied at the hand grip reaches the fastener. However the further away from the fastener the more the extension twists which gives a false reading. An extension constructed of a a more rigid material such as an impact extension will transmit the more of the actual torque applied than a chrome alloy steel.

If you use an extension on the hand grip end there are even torque wrenches made to add that of very precise dimensions.

The best thing to do is not use an extension. If you need one on the handle, get a bigger torque wrench.

Troy


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## lshadoff (Nov 26, 2002)

KA24Tech said:


> On the socket side if you add an extension, the forces applied to the wrench have two different directions horizontally (the direction you are pulling with the hand grip) and vertically (changing with the distance from the fastener). If you can stabilize the extension so that the the socket end of the torque wrench movement is minimumalized then most of the torque applied at the hand grip reaches the fastener. However the further away from the fastener the more the extension twists which gives a false reading. An extension constructed of a a more rigid material such as an impact extension will transmit the more of the actual torque applied than a chrome alloy steel.
> 
> If you use an extension on the hand grip end there are even torque wrenches made to add that of very precise dimensions.
> 
> ...


If an extension twists, then the torque wrench must be turned further until the desired torque is achieved. However, whatever the torque wrench is reading is transfered to the fastener (assuming that the extension is in a direct line with the fastener).

If the extension is really weak, then it will twist and not allow the desired torque to be applied, it will just keep twisting until it breaks, and the torque wrench will never reach the desired reading.

Lew


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## KA24Tech (Feb 2, 2004)

If the torque wrench is even one degree off of the center axis the torque reading is affected as the extension gets longer the error rate increases because the area in the arc increases thus smaller movements are larger changes in the arc angle. This off axis condition results in loss of mechanical advantage because the motion is no longer linear. Therefore a torque wrench applying one reading will be an undetermined amount lower than the actual torque applied.
The torque wrench and the user are only as accurate as the wrench is calibrated and the manner in which it is used. If the wrench is set to a certain level then it clicks or reads what it has applied to at the end of the wrench itself. The length, thickness and material flex is how they design a torque stick so that it will apply a relatively accurate 80 or 100 ft-lb from an impact applying a 300+ ft-lb input. Material strength and loss of mechanical advantage I said it changed because of flex in the material of course that is proportional to the amount of torque applied. I suggested the chrome-moly as a less rigid material not rubber-like but I didn't say I was a materials engineer either. 

Troy


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## lshadoff (Nov 26, 2002)

The torque specs for most bolts in the B14 FSM are approximately +/15% or more. For example the torque spec for the nuts on the exhaust manifold are 27-35 ft-lb. This is a 22% allowable variation.

There is an excellent web site about torque wrenches which includes a diagram of the error due to having the angle of the torque wrench extension deviate from 0 degrees:

http://home.jtan.com/~joe/KIAT/kiat_3.htm









From the graph it would take an angle of around 10* to produce this much error.

EDIT: Here is the quote which goes with the diagram:

_"From time to time people have asked me if it is OK to use an extension with a torque wrench. The answer is yes. Using an extension or reducer with a torque wrench does not affect the accuracy. Others have asked if it is OK to use a universal joint with a torque wrench. The answer is NO. Universal joints change the torque as the drive angle increases. I checked this out with my torque tester. The results are shown in Figure 8c. Don’t use universal joints with torque wrenches."_

Lew


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