An Observation

[dnschmidt]

Conventional wisdom is that you use a torque wrench to prevent OVERTIGHTENING of fasteners. What I have actually seen in practice is that normally technicians UNDERTIGHTEN bolts and nuts. An example:

A friend of mine is a motorcycle madman. He's got about 10 of these mostly Honda dirt bikes (always the latest, greatest up to datest models) but a couple of Harley's for the street as well. He works on them all the time. I recently sold him several torque wrenches. On a recent cylinder head gasket job he broke out one of his new torque wrenches and in every case the tightness that he though was sufficient for the head bolts was significantly under by at least a half of a turn to get to Honda's torque specifications. He was EXTREMELY hesitant to actually turn the bolts to the specifcation that they were suppose to be torqued to.

I've seen this in many other situations as well. My contention is that unless you're talking about a true "Crudey Rudy" most people undertorque rather than overtorque.

 

[B_Bimmer]

Small impacts and the need for speed means I almost always see too tight and the consequences of it, pulled threads and broken bolts. Therefore I find I generally err on the side of slightly loose as well and hence use a torque wrench for anything critical.

 

[zmotorsports]

I've noticed on a few occasions that the factory torque specs seem a bit on the light side as well.

One place I've noticed them in particular is on the LB7 Duramax fuel injector return lines at the injector. The OEM torque spec is 12 ft/lbs but I've found by testing with a vacuum tester that many will leak at this torque and if you simply put it together at that spec there is a highly likely chance that you'll fill your crankcase with return fuel. I have found that in order to get these to seal up properly the torque needs to be increased to about 18 ft/lbs. which is about another 35-degrees on the banjo bolts.

This is across multiple vehicles, not just an isolated scenario so I'm sure there are a multitude of other similar scenarios.

 

[kelpaso1]

Sounds like he does not know what he is doing nor understands how to use a torque wrench properly. Most bike headbolt torque is in the low ft/lb range. I don't use my 1/2 inch torque wrench for bike head bolts. Usually use a 3/8 for head bolts and a 1/4 inch wrench for top and side cover bolts that are in the inch/lb spec.

 

[will335i]

There is a lot that the ley person doesn't understand about proper torqueing and the importance of doing so.

One of the biggest is that you can continue to tighten nuts and bolts past the set torque with a torque wrench. Just because you set it at x-ftlbs doesn't mean it is going to stop turning it that just that is where the wrench clicks.

If you want an accurate torque you need the threads to be lubricated and to torque in stages.

 

[richfinn]

I don't work on motorcycles, but how can you tell if a typical TTY bolt on a car has been over or under torqued?

I guess you could measure the length??

Most damage I have encountered as a mechanic is through overtorquing, stripped threads or sheared bolts

I've seen stuff fall off cars because the bolts had zero torque applied mind you!!!

 

[unslow1]

I know that on lug nuts it seems to me like the torque spec is too tight. They do have a reputation for coming loose on some wheels so it's best to torque it.

 

[M6erfan]

My conventional wisdom has always been, follow the manufacturers specs. That way the torque value is neither under or over (if your torque wrench is accurate and proper technique is used) spec. It's pretty simple really, but I'm a simple guy.

 

[cvairwerks]

In the aviation world, it's the other direction....stuff way overtorqued all the time. Lots of times we find stuff that should be torqued to 25 in/lbs, is more like 40-60 in/lbs...

 

[Spacey_G]

If you want an accurate torque you need the threads to be lubricated and to torque in stages.

Well, when you tighten a fastener accurate torque is not even the real goal, accurate pre-load is what you're after. And a torque wrench, even under ideal conditions, is not a particularly accurate way of achieving that goal. Completely different methods are used where it really matters.

 

[Legion Prime]

If you want an accurate torque you need the threads to be lubricated and to torque in stages.

Eh, only if the torque spec specifies lubricant. It's more important for the threads to be clean in my opinion. Torquing in stages across fasteners is to prevent part deformation rather than accurize torque values. More accurate torque values can be found either by measuring fastener stretch (not always feasible) or with a hybrid, measuring to a lower torque value then turning the fastener a number of degrees.
Torque wrenches I think are more needed with smaller fasteners due to the reduced torque capacity. The difference between 5 in/lb and 15 in/lb really isn't much and can be the difference between an assembled part and one which used to be threaded. Lug nuts on the other hand have been hammered on by techs with air guns for decades and while it CAN cause problems it's usually the poor guy changing a flat on the road rather than part failure. Some parts though, regardless of size, from zmotorsports fuel lines to head bolts should always be torqued with an instrument as both over and undertightening can cause big problems.

 

[M6erfan]

If you want an accurate torque you need the threads to be lubricated and to torque in stages.

Threads only need to be lubricated if the specs call for it. Some specs specify dry threads. And there's the K-factor of the lubricant used. . .

 

[LeeG]

Although NEC 2017 has a torque requirement for electrical connections, you almost never see an electrician with a torque screwdriver. When I added some outlets to my garage, I was surprised at how much torque was required to meet spec.

 

[LXCam]

Sounds like your buddy needs his arm recalibrated D.

 

[dacan23]

M8 or M10 and below I may undertighten but anything larger not usually. Problem is with aluminum blocks and heads even using my in-lb torque wrench its easy to over tighten things 35nm/25ft-lbs and below, they are just too soft easy to strip the threads or if theres a bottom to the hole I have snapp

 

[woody 73]

I always follow the manufactures guidelines, but the thing I understand (about using anything on the threads) is a no-no; but I still use a little anti -seize (which they tell me is a no-no). I get it, but I still use it on all the wheel studs.

I know I am going to burn in hell for using it but it sure is easy the next time I need to remove those nuts.

Just my observation.

 

[Spacey_G]

Woody - I don't think there's any harm in a little anti-seize on studs. If you torque to the same number you'll technically be stretching the stud a little more, but as long as you don't break anything my sense is it's fine.

I've twisted a stud right off trying to remove a lug nut I didn't know was seized, so I see the benefit too.

 

[M6erfan]

I always follow the manufactures guidelines, but the thing I understand (about using anything on the threads) is a no-no; but I still use a little anti -seize (which they tell me is a no-no). I get it, but I still use it on all the wheel studs.

I know I am going to burn in hell for using it but it sure is easy the next time I need to remove those nuts.

Just my observation.

No issue with anti-seize on the threads, I use it often. Especially with stainless or titanium threaded in aluminum. Your can of anti-seize should have the K-factor printed on it. Easy to adjust torque setting accordingly.

 

[Rinspeed]

Conventional wisdom is that you use a torque wrench to prevent OVERTIGHTENING of fasteners.

Actually in my opinion when it comes when components that really need properly torqued fasteners it's not to prevent overtightening it's to ensure consistency among a group of fasteners.

 

[nadogail]

IMHO, a torque wrench properly used will indicate you have tightened a fastener to design specifications with a degree of uniformity.

 

[dnschmidt]

Judging from these responses I don't think most people understood what I was trying to say. My comment had little or nothing to do with torque wrenches what I stated was that from experience I have observed that most people (who are not using torque wrenches to tighten things but feel) tend to fasten bolts and nuts LESS TIGHT than they should when they are simply doing it by feel. Once they properly use a torque wrench they find that they need to additionally tighten the bolt beyond what they thought was tight enough by feel.

 

[SuperCat]

Although I find that the people I know tend to over torque by feel, my own experience is the opposite, I tend to under torque by feel. I know why - I don't want to strip threads or break off a bolt head. So, I use a torque wrench and do the best I can to put the torque value right on the money and no more. I guess I'm just the overly careful paranoid type. Lol.