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Discussion Starter · #1 ·
Everyone now and again I read a post from someone who talks about "checking the torque" on their already-tightened bolts. Is there really any logic to doing that? I've never really understood the practice. The only way to measure torque is to be moving the bolt, so "checking the torque" must translate into "loosening and retightening". And what would be the sense in going over my bike and loosening and retightening everything?

I suppose I could run through with an allen wrench and check quickly for obviously loose bolts, but I wouldn't use the phrase "checking the torque" to describe doing that.

I do keep an eye open for loose bolts or other things that might me amiss. But once I torque a bolt down, I leave it alone unless there's an obvious problem.
 

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Actually it's really simple....

all you are doing when checking torque is, with a click type torque wrench, setting the wrench to the proper torque setting, and ckecking that the wrench clicks and observing the bolt. You're looking for movement or the feel of movement of the fastener before the wrench clicks. With a beam type wrench it's pretty much the same except you are visually observing the torque reading. Checking torque doesn't require loosening fasteners and the retightening them. The idea is to check that the fastener is tightened to the proper torque without making it any tighter than it already is. It's a simple concept and very easy to do. I've never found a fastener on a bike that will tighten on it's own. There are components that will, freewheels, pedals, etc. but not a fastener. If any thing they come loose from vibration etc. So on torque critical parts it makes perfect sense to check em with a torque wrench. Back in the day the most common fastener to loosen was the nondriveside crank arm bolt on a square taper bb. I used to check crank bolts at least once a month, and you KNEW that the nondrive side would be loose (not dangerously so, but deffinately under torqued). So checking it with the torque wrench and bringing it back up to spec just made sense.

Bottom line is, you're simply checking torque critical bolts with the torque wrench to make sure they are still in spec. It's easier and faster than checking with an allen wrench, finding a loose one and having to switch to the torque wrench to get it right. It saves you from switching tools when you find a loose one. And it's more accurate than using an allen and trusting to your fingers to tell you that your crank bolt was 50 lb/in low, or that your disc caliper mounting bolts had loosened up 15 lb/in. :thumbsup:

Good Dirt
 

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People seem to sometimes get confused about "checking torque." I knew I had read something about it, and just found the description I had read in "Zinn & The Art of Mountain Bike Maintenance."

Torque should be measured while the bolt or nut is rotating. So checking torque on a stationary bolt (nut) doesn't make a lot of sense. The reason for this is something termed static friction, or the amount of force required to get that bolt (nut) rotating by overcoming friction. Static friction isn't included in torque requirements for a fastener.

Sometimes the force required to overcome static friction is greater than the required torque on a fastener. So if you are torquing a fastener that isn't rotating, for example "checking" it, you run a good chance to undertorque because of static friction.

If you are concerned about the torque on a certain fastener, the recommended practice is to loosen it, and then torque it using a constant steady pull until you reach the required torque.

I hope this makes sense.

edit: That's what I get for trying to write something technical too late at night
 

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Discussion Starter · #5 ·
4slomo said:
Sometimes the force required to overcome static friction is greater than the required torque on a fastener. So if you are torquing a fastener that isn't rotating, for example "checking" it, you run a good chance to overtorque because of static friction.
And that is essentially what led me to ask the question. I recently read a post by someone who'd stripped a key bolt whilst "checking torque".
 

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4slomo said:
Sometimes the force required to overcome static friction is greater than the required torque on a fastener. So if you are torquing a fastener that isn't rotating, for example "checking" it, you run a good chance to overtorque because of static friction
I also have this suspicion of over-tightening from checking. Didn't actually know the technical details involved, (and this following example doesn't seem to relate to the static friction explanation), but it seemed that sometimes when i torque a bolt to spec, and torque it again straight after, it would still rotate some more, even when the first time the pointer was at the right mark.
 

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Checking the torque on a bolt without turning it says nothing for the actual tightness of that bolt. All it says is that the static friction is greater than the torque required. This is typical because of rough surfaces binding, galling, and corrosion. The part, however, can still have a low enough actual torque value to cause damage, slip, and loosen further as stresses are placed upon it, though I think that would be hard to find on a properly maintained mountain bike.

On the other hand you don't want to further torque an already correctly tightened bolt, for obvious reasons like damaging the part (cracked stem face plates anyone...), breaking the bolt, or stripping the threads.

These two obvious common sense issues translate into loosening fasteners before torquing them to spec again. This is not something I typically do before each ride, but I check on occasion with basic maintenance, chasing down creaks, or changing out parts.
 

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4slomo said:
...
Sometimes the force required to overcome static friction is greater than the required torque on a fastener. So if you are torquing a fastener that isn't rotating, for example "checking" it, you run a good chance to overtorque because of static friction.
...
This is wrong.

The static friction means that it requires a larger torque to move the bolt than what it was torqued at.

So, if you have a torque wrench and you torque a bolt to 35 in-lbs and then you "check it" you should hit 35 in-lbs without it moving. Your check really only tells you that your previous torque plus the static rotational resistance add up to at least 35 in-lbs.

Having fasteners move on another round of torque is very very common through multiple bolt systems, depending on the configuration it could take 3-10 rounds of torque to get everything equal and to spec. I go back an forth between my two pinch-bolts on my cranks at least 5 times before I'm satisfied they are properly torqued.

Also, you should consider lube. If a bolt is lubed it will create a larger clamping force than a non-lubed bolt for the same torque. I know most specs don't call out if there is lube, since most bolts are recommended to be lubed I always assume lubed.

Torque can loosen over time through vibration and "torque relaxation". Vibration is the main problem with bikes and for bolts prone to it that is where thread locker comes in handy.

So in summary, checking torque is a good practice as it tells you if you have a decent loss of torque for some reason, but it doesn't guarantee that that bolt is torqued all the way to spec.
 
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13pumps said:
rechecking the torque on bolts is an every day occurrance in aviation. if there is a range check at the low end.
Care to elaborate for those of us who are not airplane mechanics? Do you loosen then tighten, or just "check." I suppose if it's good enough on an airplane, it's good enough for my bike...
 

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nepbug said:
So, if you have a torque wrench and you torque a bolt to 35 in-lbs and then you "check it" you should hit 35 in-lbs without it moving. Your check really only tells you that your previous torque plus the static rotational resistance add up to at least 35 in-lbs.
That is how I have always checked torque on my bikes. I am wondering two things now:

1) How much of a difference the rotational resistance makes if the bolt is clean and not muddy/rusty. (obviously depends on the fastener size, thread size, original torque, etc.)

2) How much leeway (+/-) is really built into the torque specs?
 

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BumpityBump said:
That is how I have always checked torque on my bikes. I am wondering two things now:

1) How much of a difference the rotational resistance makes if the bolt is clean and not muddy/rusty. (obviously depends on the fastener size, thread size, original torque, etc.)

2) How much leeway (+/-) is really built into the torque specs?
For number one a lot of things come into play, but a good rule of thumb I go buy is that it takes approximately 10% more torque to overcome static friction of a torqued bolt.

For number two, it depends on a lot of things again. In most industrial applications there is a good amount of leeway in there before the bolt breaks, but in biking where weight, fastener size, etc come into play a bit more I would suspect your factor of safety isn't as high as other applications.
 

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sddave111 said:
What about checking bolts which have threadlocker? If I check the torque and the bolt moves, have I just ruined the effect of the threadlocker (ie - do I now need to remove bolt to clean & reapply)?
I occasionally check the shock pivot bolts on my bike. They were installed with thread locker. I just give them a slight righty-tighty twist to see if they move. If they do, I unscrew them all the way, reapply thread locker and torque to spec. (On one of my bikes, I put medium thread locker on the pivot bolts prior to building it up. I've never had any of them loosen enough to fail the above test so as to require new thread locker.)

But you're right - if you loosen the bolt and then re-torque it, that defeats the purpose of the thread locker. That's why I only check to see if the bolt is loose. I don't apply enough torque to break the bond, only enough to tighten it slightly if it's quite loose.
 

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I roadrace sport bikes (with motors) and I do most of my own wrenching. I've been told that you don't 'check' torque per se, if you torqued it properly to begin with you can check to see if it's tight. But, if you are concerned about the torque then loosen it and re-torque it. Also, you definitely don't figure out the torque value by taking a wrench to it to see what it comes to. Besides on a motorcycle ya safety wire stuff that needs to be torqued... don't want it coming loose at 150.
 

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Actually it's really simple....

all you are doing when checking torque is, with a click type torque wrench, setting the wrench to the proper torque setting, and ckecking that the wrench clicks and observing the bolt. You're looking for movement or the feel of movement of the fastener before the wrench clicks. With a beam type wrench it's pretty much the same except you are visually observing the torque reading. Checking torque doesn't require loosening fasteners and the retightening them. The idea is to check that the fastener is tightened to the proper torque without making it any tighter than it already is. It's a simple concept and very easy to do. I've never found a fastener on a bike that will tighten on it's own. There are components that will, freewheels, pedals, etc. but not a fastener. If any thing they come loose from vibration etc. So on torque critical parts it makes perfect sense to check em with a torque wrench. Back in the day the most common fastener to loosen was the nondriveside crank arm bolt on a square taper bb. I used to check crank bolts at least once a month, and you KNEW that the nondrive side would be loose (not dangerously so, but deffinately under torqued). So checking it with the torque wrench and bringing it back up to spec just made sense.

Bottom line is, you're simply checking torque critical bolts with the torque wrench to make sure they are still in spec. It's easier and faster than checking with an allen wrench, finding a loose one and having to switch to the torque wrench to get it right. It saves you from switching tools when you find a loose one. And it's more accurate than using an allen and trusting to your fingers to tell you that your crank bolt was 50 lb/in low, or that your disc caliper mounting bolts had loosened up 15 lb/in. 👍

Good Dirt
If you set your torque wrench to the specified torque for the fastener you're checking and the wrench clicks and there is no movement of the fastener, how do you know the fastener was not over-torqued? The only way to accurately check the torque of a suspected fastener is to loosen it and re-torque it. In aviation any device or tool that measures anything must be calibrated. A click type torque wrench that has been dropped could have damage and should be checked for accuracy.
 

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just check it
----------------------
I have a seatpost wedge bolt on Giant XTC frame, and after some rides it unwinds a bit...set to 10.2nm,
I find it around 8nm sometimes

every few rides I slap the torque wrench on and retighten to spec. after 4 or 5 rounds it then stays put at 10.2
(or whatever it wants to be at...I get a click, I stop)

after this game of chase the bolt....
it only does the unwinding act again if I have to actually loosen it with a wrench, then it does the every few rides game until it decides to stay put. weird but whatever...wedges suck but I am stuck with it
 

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just check it
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I have a seatpost wedge bolt on Giant XTC frame, and after some rides it unwinds a bit...set to 10.2nm,
I find it around 8nm sometimes

every few rides I slap the torque wrench on and retighten to spec. after 4 or 5 rounds it then stays put at 10.2
(or whatever it wants to be at...I get a click, I stop)

after this game of chase the bolt....
it only does the unwinding act again if I have to actually loosen it with a wrench, then it does the every few rides game until it decides to stay put. weird but whatever...wedges suck but I am stuck with it
Try adding a dab of chain lube to the bolt before torqueing it next time.
 
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