Why So Much Disdain For Using Torque Tools

[Trav]

I have a question I would like to ask about torque wrenches.
Here at BITOG it seems any time anyone suggest using one for spark plugs, oil drain plug, lug nuts, etc the comments begin to fly.
“My feel is good enough”
“I have been doing this for years I can tell”
On an on like they are in some way feeling like a noob or posses less skill for using one, some seem to be actually insulted if asked if they torque the fastener and get very defensive like someone just challenged their experience or skill.

Manufacturers spend time and money putting together torque specs for a reason, in over 35 years of working with fasteners every day my feel is a good as anyone’s but I still don’t count on my feel to be exact or good enough to guess at specs.
Personally I feel I have done a better job when I use the torque wrench and even mark critical fasteners after I torque them.

Is this an American thing? You know close enough for this job or just a feeling of being inferior for some reason?
In Europe the sign of a good mechanic or a craftsman is one that reads specs and uses them. Those who use the good enough routine are considered poor or second rate.

Don’t get me wrong I am not judging one way or another, it’s just a question.
IMHO if I spend good money on quality torque tools I want to use them for what they were intended.

 

[scurvy]

I don't get it either, Trav.

If the manufacturer thought hard enough about it to put a torque spec in the factory manual, that says to me that it's incumbent on me to follow it.

 

[Eddie]

Misplaced Ego thing.

 

[rationull]

I can see the attitude that you don't *need* to use torque tools in most cases, such that if you don't have them around or accessible you can still do the job. However, I'm with you in that I don't get why it seems to be discouraged so much when it is possible to use them.

I have two torque wrenches -- a big clicker for lug nuts and other high torque items and a small beam one for low torque items. Since I bought them, and the manuals list torque specs, why not use them?

From reading some comments you'd think they were a serious pain to use or something. I don't get it.

 

[Mr Nice]

Quote:
IMHO if I spend good money on quality torque tools I want to use them for what they were intended.


Thats probably cause you make a living and need torque tools, unlike Joe the plumber type DIY at home mechanics working on their car.

 

[river_rat]

My guess is that many cannot afford them in this country(?)
Just a guess.

 

[dave munson]

On one hand, it's the lack of a quality mechanical orientated education.

On the other hand, if the device is made in China, should standard torque values be used or tightened as hard as possible with a plastic toy wrench?

 

[eljefino]

What is typical breakaway torque? 2x what you should get it down to? Can muscle memory remember this, if you're doing the whole job in a sitting? I don't label my piles of parts and bolts either even when doing something big like a FWD clutch. Just put them down, carefully, with a zen memory of what they do.

There are charts for standard torque for standard fasteners. So one 8mm bolt should feel like the next.

Rust adds to both breakaway torque and what you should redo it to. I'm not putting all new fasteners in every time something comes apart.

I use a torque wrench for axle nuts, head bolts, and anything with a few threads going into aluminum.

Something mission critical that keeps the wheels on will have a cotter pin/castle nut system or other locking device. Lugnuts I go by feel, and check aluminum rims the next day.

 

[Pablo]

That must be a new thing. The attitude on BITOG used to be that your torque wrenches should be used for all threaded fasteners, calibrated at least annually, preferably every six months, traceable to NIST and that you certainly could not trust a torque tool in the as purchased conditions.

Times do change.

 

[Stu_Rock]

Originally Posted By: Trav
some seem to be actually insulted if asked if they torque the fastener and get very defensive like someone just challenged their experience or skill.
It is a challenge to their experience and skill.

I would make that challenge.

 

[jstutz]

I have been working on cars for many years and i still use torque wrenches when doing transmission pans, diff covers, intake stuff ect. Not because i dont think i can guess close enough, but because i just like to know it is done exactly correct. I dont however use them on my oil drain plugs as none of mine are sensitive to torque and i know better than to over tighten them. To each there own. My father in law has rebuilt so many engines and vehicles it is crazy and i dont think he has ever used a torque wrench except for maybe head bolts or something very sensitive.

 

[tonycarguy]

For important things like wheel nuts, I use a torque wrench. For oil drain plugs, I don't use a TW because I go by feel and even if my feel is a little off, it's no big deal.

The reason the mfr posts torque values is because it's more specific than saying, "Tighten the oil drain bolt kinda like this much" -- you can't specify it in a book without stating a precise value. Just like a food recipe will tell you to use 1/2 cup sugar because it can't just say "well, add kinda like this much sugar". Experienced chefs never measure

 

[sandy_d]

I don't understand this resistance to using the torque wrench either. As long as the tool is decent quality and you can trust the calibration on it I would certainly think it would be in anyone's best interest to use it.

After all when they assembled your vehicle the bolts were torqued with a professional air tool that is properly calibrated and functions just like a manual torque wrench.

I think if you have anything to worry about it is the careful threading of the fastener before you tighten it down. Sometimes personal experience can mean the difference between a properly installed fastener and a cross threaded one.

 

[spasm3]

I use a torque wrench on things that need it. Head bolts intake bolts axle nuts and always always on my wheels( never a warped rotor since i do this, i take it with me to the tire shop!). I just never need to break it out for oil pan bolts and spark plugs.

 

[justinf89]

I use a torque wrench for whenever I can find a value. Can't say my harbor freight wrench is very accurate but I've stripped too many threads over the years so I use it from now on.

 

[IndyIan]

I guess I change my wheels at least twice a month in the summer for autocross, and my torque wrench is a the same length as the lug wrench so after a while I just use the same pressure on the lug wrench as I do using the torque wrench.
Spark plugs I have enough practice with too, but something that is critical like head bolts and I have little experience with, I'll break out the torque wrench.

 

[demarpaint]

I guess I'm guilty, or at least partially guilty. I use a torque wrench for just about everything that I can find a published spec on. I don't use it for the oil drain plug though, maybe I should. I've been changing oil since the 70's and never stripped a drain plug, but I've removed some I could swear were torqued down with an impact wrench to the max.

Great topic!

 

[JOD]

I'm one of the loudest deniers of torque wrenches, so I should probably explain my position in detail. Before I answer your question though, I want to clarify two things:

1. when I talk about the problems inherent to "torque tools", I'm talking about the typical 'torque wrench', not an angle torque gauge/tool or a tool that actually measures the tension of the joint. For some joints where the joint tension is critical (a car head gasket would be an example), those tools or methods are helpful, if not imperative.

2. I'm not 'against' torque wrenches per se, but I feel that for most applications they range from redundant to counterproductive, depending on the application.

Another thing I should probably mention is that this isn't theoretical mumbo jumbo for me. I've dealt with it in my professional life for most of my adult life, and it's that experience (and a lot of research after having poor results with torque wrenches) which has led me to this conclusion. This experience has been in the bicycle industry though, not automotive. Before anyone says "well, those are just bikes", keep in mind that the tolerances are much, much closer, the materials are several orders of magnitude closer to their yield/failure point, and many of the interfaces are more critical, with fewer safeguards in place. In other words, if your 130 gram magnesium stem's titanium bolt shears off your 180 gram handlebar, you're almost certain to need dental work. The only thing analogous in the automotive world would be high-end racing parts designed to fall apart after the finish line.

OK, with that out of the way, here's why I don't really care for torque wrenches, and use them sparingly: they imply a level of precision which isn't even remotely close to reality.

That's the Cliff's notes. If you want the long version, I'd suggest giving this guy's blog a read, where he details his thoughts more eloquently than I can: LINK

Here's the crux of the issue: many people tend to thing that bolt friction (nut factor, or K)=joint tension. It doesn't, it's simply an estimated proxy for it. Other people realize this, but don't actually understand just how much variance there is between nut factor and actual joint tension. There are volumes written on this subject, but basically nut factor can misrepresent actual joint tension by several HUNDRED percent, depending on the variables. In a perfect world, such as the example in this guys blog (using virgin surfaces and aerospace-grade fasteners), the variance is up to 100%!! Take a 10 year old, corroded cylinder head and a new spark plug (whose plating's friction coefficient is completely unknown), and all bets are off. That's why when people argue about the most accurate brand of torque wrench, I have to roll my eyes; it's like asking "what's the best truck scale to measure these feathers". It doesn't really matter if the accuracy of your torque wrench is 10% or 1%, and if you believe that does, you simply don't understand the relationship between K and bolt tension.

I have to say, many of the responses to your question simply reinforce my belief. People seem to look derisively on those who don't use torque wrenches as being "amateur", or "letting their ego get in the way". Obviously, they feel that using a torque wrench provides a more accurate, or professional result. The reality is that typically that's simply not the case. The fact is, for most joints there is a very, very wide range of acceptable tension, and "operator feel" is typically well within the acceptable range for most joints--and of similar accuracy to K. In other words, the guy who says "it's tight enough" is just about as likely to get it right (or wrong) as the guy using a torque wrench.

 

[Stu_Rock]

Fair enough, but I'm still not changing my opinion. Especially for small fasteners (specifically, the small wrenches used on them), it's difficult to have a good "arm sense" for torque. If you asked a population of wrenchers to tighten by feel to a specific torque, I bet that the range of torque values you would get would be at least a factor of 2 (or 50% to 200% of the requested value), which is larger than the errors observed in your link. I also expect similar results for large wrenches with low torque (spark plugs in aluminum heads).

In cars, I view the torque wrench as having three main purposes, with different fasteners having different needs:
1. prevention of overtorque in fasteners that would be bad if broken (spark plugs)
2. prevention of undertorque in things that can loosen themselves (wheels, things with actuators)
3. consistency (things with gaskets, wheels/preventing rotor warping)

For #1, engineers should account for at least a factor of 2 in the joint tension. For #2, the tension is not really what matters. Rather, it's the loosening torque. For that, the torque wrench reading is a very good proxy. Something that is constrained by both #1 and #2 is poorly designed (Ford modular v8 spark plugs; many Chrysler suspension fasteners).

#3 is a big problem. I agree that joint tension is not necessarily consistent (as an aside, we noticed it firsthand at my old job where we frequently did an ASTM test procedure that called for a torque wrench, but we also had a load cell in the fixture that measured tension directly). But you are still more likely to be consistent with a torque wrench than without. More directly, I contend that the last sentence in your post is almost certainly provably incorrect.

 

[JOD]

Originally Posted By: Stu_Rock
Fair enough, but I'm still not changing my opinion. Especially for small fasteners (specifically, the small wrenches used on them), it's difficult to have a good "arm sense" for torque. If you asked a population of wrenchers to tighten by feel to a specific torque, I bet that the range of torque values you would get would be at least a factor of 2 (or 50% to 200% of the requested value), which is larger than the errors observed in your link. I also expect similar results for large wrenches with low torque (spark plugs in aluminum heads).



John Bickford would disagree, and he's researched this exact question in detail. These are his results:

Torque control with hand wrench - 30%
Small air torque tool - 35%
Click type torque wrench - 60-80%
Turn of nut - 15%
Load indicating washers - 15%
Strain gaged bolts - 1%
Air powered impact wrench - 100-150%
Bolt stretch - 3-15%
Ultrasonic - 1-10%
Operator feel - 35%

You can read more of the methodology of how he determined this in his "Handbook of Bolts and Bolted Joints". It really is a great read, if you're interested in this stuff, and you're an insomniac. This particular part is on page 674--you can probably find it on Google books. I think Bickford's research is sound, and he's pretty much the preeminent guy in this field.

Originally Posted By: Stu_Rock
you are still more likely to be consistent with a torque wrench than without. More directly, I contend that the last sentence in your post is almost certainly provably incorrect.


I think that Bickford has, in fact, proven to the contrary, at least to my satisfaction. I'd urge you to read the full text sometime when you're really bored, and make your own determination--no need to take my word for it. For a joint that is really tension-critical, like head gaskets (as you mentioned), that's why manufacturers typically include angle torque specs, or utilize TTY bolts. Why? Because it's much more accurate.