Over-tightening of bolts and nuts by powertools

[ThosL]

The challenge of removing certain bolts and nuts in trying to do my own mechanical work got me thinking about how it is so easy for mechanics to over-tighten then with the power tools at their disposal.  So the next guy, especially those working on their vehicles who don't have power tools are then in a fix and can't get parts off!!  

 

Have there been any studies on possible risks that would come from under-tightening? Frankly it looks like overkill is the name of the game in society these days with all the security state, insurance, and paranoia in general of "what might happen" if reasonable actions were permitted.  And I doubt that lightly tightened things would come off.  

[=CC=]

I guess it would depend on the part.  I wouldn't want to drive around with lightly tightened suspension bits, or lug nuts. 

[heartless]

There are torque specs for every bolt/nut for a reason, and they should be followed.

Over torquing will break things, under torquing will allow things to work loose. Either situation is not good.

 

even lug nuts have a torque spec.

[ThosL]

Is there any commercial or other counter, push-back if a mechanic "kills" the bolts or nuts?  Have any studies been done to show real risks if the tightening is not cinched down fully?  

[Numbchux]

And I doubt that lightly tightened things would come off.

 

Vibration is powerful at working hardware loose. That's why many suspension components have cotter pins (tie rod ends, ball joints, old-gen axle nuts), or use locking nuts (sway links, new gen axle nuts). That's why virtually every fastener on an airplane has safety wire through it (my wife works at Cirrus Aircraft).

 

Not to mention corrosion. A fastener torqued to the minimum spec becomes rusted solid.

 

On most hardware, there's a fine line between adequately torqued and broken. So I don't think mechanics are just slamming their impact wrench on everything and hammering it home. Even with the right tools and experience to extract a broken bolt, it's still a crappy job, and most mechanics are paid by the job, which means broken bolts come out of their pocket.

 

 

Ever had something major fall off your car? I've had a couple wheels fall off, a brake drum (which, of course, took the wheel with it), ball joint, brake caliper. Not to mention many close saves. I'll take every minute of struggling with tough hardware over one of those.

Edited March 30, 2018 by Numbchux

[ThosL]

Good analysis, thanks.  I think we should all be using neverseize, teflon tape and similar products when necessary.  I would just hope mechanics would be mindful of necessary vs. excess force.  

[GeneralDisorder]

If they were over torqued they would be stretched, stripped, or broken. Sounds like you need a bigger cheater pipe.

 

GD

[idosubaru]

Have there been any studies on possible risks that would come from under-tightening?

 

 

 

And I doubt that lightly tightened things would come off.

No. That’s why there are torque values.

Wheels, axle nuts, crank shaft bolts are frequently known to loosen and come off.

 

What are you looking for - a study that says loose bolts can make things fall off? That’s foggy and unclear what and why you’re asking.

 

in some sense there is no answer or it depends on what, why, how much, etc

[Gloyale]

I will say that on subes in particular, i encounter many previously over tightened bolts.

 

Usually it's the Timing belt covers, or water pump bolts.  Those little M6 going into aluminum or captive plastic get blown out by even a 1/4" drive air or electric ratchets.  Those little M6 bolts don't ever need ore than about 7 ft/lbs tops.  No fun.  got to helicoil to fix the stripped threads.  But I've seen a few where the "ear" of the block that the timing covers bolt too snapped off.

 

also seen timing belt tensioner bolts, and idler bolts too tight to the point of stripping.  Power steering pump bracket bolts too.

 

Many folks are not used to working with small fasteners going into aluminium.

[forester2002s]

When I buy new tires, I invariably find that the wheel lug-nuts have been overtightened.

 

So it's a routine for me, that every time my car comes back from a shop:

 

- I untighten the lug-nuts using a socket & T-bar;

- Then I retighten using the car's spare-wheel wrench.

 

That way, if I have to change a tire on the road-side, I can at least get those lug-nuts loose.

[rocketman]

When it comes to lug nuts, I use a torque wrench, mostly so Roters don't warp.

[ThosL]

I have never had a bolt vibrate loose; I tighten reasonably, don't make a point of killing it.  So the whole idea is reasonable force; mechanics are much more aware of torque specs which become critical in certain applications.