How to re-torque a bolt?
#1
How to re-torque a bolt?
Hey folks. When re-torquing a bolt that is not tight enough, can one just tighten it straight away to spec or is it best to unscrew it a bit and then torque it to spec?
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If the bolt isn’t tight enough, just torque it to spec. That’s the way you would torque a freshly installed bolt anyway.
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It's sort of a decision you have to make for the unique circumstances that you are having and seeing for that particular bolt or nut that you want to tighten. Stiction is a thing sometimes. And if the bolt or nut is almost there but not quite if may not break free of the stiction for that last little bit of torque. Also, if the threads are not in good condition, corroded or contaminated with certain substances, then it' might be a good idea to loosen first. (better maybe undo it completely to clean it up and put a little grease on it)
Conversely when trying to undo bolts or nuts, I've sometimes found that if they won't turn to loosen, I can sometimes tighten them a tad more and get them to break free of whatever is keeping them from turning and then they loosen easily. Though seldom on a bicycle have I had to do this.
Conversely when trying to undo bolts or nuts, I've sometimes found that if they won't turn to loosen, I can sometimes tighten them a tad more and get them to break free of whatever is keeping them from turning and then they loosen easily. Though seldom on a bicycle have I had to do this.
Last edited by Iride01; 11-24-23 at 09:35 AM.
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I'm with the back off and retighten to torque spec crowd. That's what I was taught. What I violate is the dry bolt only when needing a torque spec rule. I add some sort of lube or locker to most all my threaded fasteners.
Funny story about bolt torque and experience and ego. As the whole small bolts replacing big ones and AL or carbon fiber constructs became the thing many/most pro mechanics were reluctant to use a torque wrench for tightening stems, bars, posts and such. They, as I was/am, very experienced with how strongly to tighten the various bicycle fittings that were the norm in the 1970s/1980s. "I know how tight to make it" was a common claim. For the LBS level of wrenching this was good enough most of the time, between the experience with both big and small bolts and that we tend to only touch a repair bike more than once or twice in a season a "good enough" tightness is fine. But at the pro ranks the bikes see nearly daily attention from the mechanics. At a Tour De France a Park Tool guy (I think he was a Park guy?) went around with his own torque wrench and was checking various teams bikes on his own. What he found was that at the start of the tour the mechanics had set the various torques about right, as though they did use a torque wrench before coming to the race. But as each day's stage wear and grime was washed off and checked for the hardware would get a small amount more tightening "just to make sure". By mid tour this guy found many fasteners were far tighter than they should have been.
This just reinforced my belief that the bolt/nut should be slightly loosened before retightening when checking for torque spec. And that even pros should learn new ways. Andy
Funny story about bolt torque and experience and ego. As the whole small bolts replacing big ones and AL or carbon fiber constructs became the thing many/most pro mechanics were reluctant to use a torque wrench for tightening stems, bars, posts and such. They, as I was/am, very experienced with how strongly to tighten the various bicycle fittings that were the norm in the 1970s/1980s. "I know how tight to make it" was a common claim. For the LBS level of wrenching this was good enough most of the time, between the experience with both big and small bolts and that we tend to only touch a repair bike more than once or twice in a season a "good enough" tightness is fine. But at the pro ranks the bikes see nearly daily attention from the mechanics. At a Tour De France a Park Tool guy (I think he was a Park guy?) went around with his own torque wrench and was checking various teams bikes on his own. What he found was that at the start of the tour the mechanics had set the various torques about right, as though they did use a torque wrench before coming to the race. But as each day's stage wear and grime was washed off and checked for the hardware would get a small amount more tightening "just to make sure". By mid tour this guy found many fasteners were far tighter than they should have been.
This just reinforced my belief that the bolt/nut should be slightly loosened before retightening when checking for torque spec. And that even pros should learn new ways. Andy
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AndrewRStewart
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#7
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If you're using a beam-type torque wrench, you can see how much a bolt is over-torqued; if you're using a click-type torque wrench, the only way to know that a bolt is at the correct torque (vs over-torqued) is to back off a bit and then tighten it.
Of course, if a bolt is visibly loose, then just have at it.
#8
I use a torque wrench on cars and on boat engines but seldom on bikes. Most of the bolts are so small that I tighten by hand with a small wrench. No vibration with a bike unlike motorized vehicles and if there is a worry then there are usually special washers designed to keep a fastener from loosening. Common with bike in the 1970's were broken bolts used to fasten the front derailleur to the bike frame. Being 8mm and hardened steel (and more brittle) if someone use a socket wrench they were going to apply enough torque to snap the head off.
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"If you're using a beam-type torque wrench, you can see how much a bolt is over-torqued" Koyote
Unsure about this as I believe you're also sensing the bolt's stiction or corrosion. I was taught that the torque wrench readout (and we could talk about the difference between a scale and a gage) is only valid while the bolt was turning. Andy
Unsure about this as I believe you're also sensing the bolt's stiction or corrosion. I was taught that the torque wrench readout (and we could talk about the difference between a scale and a gage) is only valid while the bolt was turning. Andy
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This is what I learned as well. The applied torque is supposed to be stretching the threaded part of the bolt (using the threads as an inclined plane). When the bolt isn't turning, there's static friction added to the torque wrench reading, which renders the wrench reading inaccurate. Also, the bolt's threads are generally lubricated to get the proper amount of stretch for a given applied torque.
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This doesn't actually answer the original question, but nicely shows what happens when a bolt is tightened. (
)
The consensus ^^ supports at least backing off, then re-torquing to spec.
The consensus ^^ supports at least backing off, then re-torquing to spec.
#13
It's sort of a decision you have to make for the unique circumstances that you are having and seeing for that particular bolt or nut that you want to tighten. Stiction is a thing sometimes. And if the bolt or nut is almost there but not quite if may not break free of the stiction for that last little bit of torque. Also, if the threads are not in good condition, corroded or contaminated with certain substances, then it' might be a good idea to loosen first. (better maybe undo it completely to clean it up and put a little grease on it)
#14
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Agreed on all but the very last point. Many fastener torque ratings are quoted dry - greasing will potentially let you stretch or strip the fastener before you reach the stated torque. This is possibly more applicable to diesel engines than bike parts, but is something to bear in mind.
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![WTF](images/smilies/wtf.gif)
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Now if we're talking about a cotter pin... Andy
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A good way to damage a crank arm's square taper is to retorque its bolt. Do it once during installation and forget it.
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How is it known that the bolt isn't tight enough if not using a torque wrench?
If you don't loosen a bolt first, you wouldn't know (unless using a non-click wrench) that your bolt could already be over-tightened (past the torque rating).
#19
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As a former lead bicycle mechanic, if I find it better to just re-torque it to the proper specs. However, if there is more than one bolt not at the correct torque specification, loosen then torque them all to spec. Stem bolts should have a little bit of blue Loctite on them to help prevent loosening. Some people use grease, but with grease, I find it easier to over-torque the bolts, than either dry or have blue Loctite.
#20
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I'm with the back off and retighten to torque spec crowd. That's what I was taught. What I violate is the dry bolt only when needing a torque spec rule. I add some sort of lube or locker to most all my threaded fasteners.
Funny story about bolt torque and experience and ego. As the whole small bolts replacing big ones and AL or carbon fiber constructs became the thing many/most pro mechanics were reluctant to use a torque wrench for tightening stems, bars, posts and such. They, as I was/am, very experienced with how strongly to tighten the various bicycle fittings that were the norm in the 1970s/1980s. "I know how tight to make it" was a common claim. For the LBS level of wrenching this was good enough most of the time, between the experience with both big and small bolts and that we tend to only touch a repair bike more than once or twice in a season a "good enough" tightness is fine. But at the pro ranks the bikes see nearly daily attention from the mechanics. At a Tour De France a Park Tool guy (I think he was a Park guy?) went around with his own torque wrench and was checking various teams bikes on his own. What he found was that at the start of the tour the mechanics had set the various torques about right, as though they did use a torque wrench before coming to the race. But as each day's stage wear and grime was washed off and checked for the hardware would get a small amount more tightening "just to make sure". By mid tour this guy found many fasteners were far tighter than they should have been.
This just reinforced my belief that the bolt/nut should be slightly loosened before retightening when checking for torque spec. And that even pros should learn new ways. Andy
Funny story about bolt torque and experience and ego. As the whole small bolts replacing big ones and AL or carbon fiber constructs became the thing many/most pro mechanics were reluctant to use a torque wrench for tightening stems, bars, posts and such. They, as I was/am, very experienced with how strongly to tighten the various bicycle fittings that were the norm in the 1970s/1980s. "I know how tight to make it" was a common claim. For the LBS level of wrenching this was good enough most of the time, between the experience with both big and small bolts and that we tend to only touch a repair bike more than once or twice in a season a "good enough" tightness is fine. But at the pro ranks the bikes see nearly daily attention from the mechanics. At a Tour De France a Park Tool guy (I think he was a Park guy?) went around with his own torque wrench and was checking various teams bikes on his own. What he found was that at the start of the tour the mechanics had set the various torques about right, as though they did use a torque wrench before coming to the race. But as each day's stage wear and grime was washed off and checked for the hardware would get a small amount more tightening "just to make sure". By mid tour this guy found many fasteners were far tighter than they should have been.
This just reinforced my belief that the bolt/nut should be slightly loosened before retightening when checking for torque spec. And that even pros should learn new ways. Andy
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You can usually just tighten the bolt right up to the recommended torque setting (called "spec") without loosening it first. Imagine the bolt is like a spring - tightening it straight to spec pushes the parts together with the right amount of force. Loosening first might damage the threads, so it's best to avoid unless a mechanic specifically tells you to do it for a certain job.
#22
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Loosening also obviously carries the danger of moving whatever the bolt is holding out of position.
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Of course it depends on how far under-torqued it is.
Figure that static friction can be significantly greater than sliding friction, so there will be "breakout" torque which is greater than the torque the bolt was tightened.
So, 2 scenarios, both calling for a torque of 100lbft. Also a friction difference of 20%
1- the bolt was last tightened to LT 70#'. It won't move until torqued to up to 84#', then you can continue to 100.
2- the bolt was tightened to 90#'. It won't move until you apply the breakout torque of 108#', then will jump to that torque, ending up overnight.
Proper technique is to torque bolts in a single smooth motion, so you're working with the sliding friction factored into the spec.
This is why it always takes greater torque to loosen a bolt than what it was originally torqued to.
Last edited by FBinNY; 05-28-24 at 09:40 PM.
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