Bicycle Mechanics - Crank Bolt Torque - new crank vs broken in - square taper

My new Campy crank has a suggested ~28.5 ft lbs for the crank bolt torque when installing. I installed it to 20ft lbs and it seems very solid. The crank and bolt were hand tight and I went a few full turns past that with seating the crank arm on the spindle to get to 20 ft lbs of torque.

Getting to my question... in a few crank bolt torque threads on this site, I'd read that when removing and reinstalling a crank, you don't need to torque it to the full specification when reinstalling. Is this correct?

Appreciate any input.

somegeek

No.

Torque it to the full specification every time. What "feels" solid to your hand is not relavant to the forces your legs will put on it.

Thanks for the replies all. Will do! :)

Is this correct?


100% incorrect.

I'd be a pretty confused OP at this point!

Operator, you seem to be saying that the torque required on reinstallation is less than that required on initial installation. If that's what your saying, please explain why.

Road Fan

My new Campy crank has a suggested ~28.5 ft lbs for the crank bolt torque when installing. I installed it to 20ft lbs and it seems very solid. The crank and bolt were hand tight and I went a few full turns past that with seating the crank arm on the spindle to get to 20 ft lbs of torque.

Getting to my question... in a few crank bolt torque threads on this site, I'd read that when removing and reinstalling a crank, you don't need to torque it to the full specification when reinstalling. Is this correct?

Appreciate any input.

somegeek

The only place I've ever seen anything like that recommendation is here (http://www.bbinstitute.com/DX%20Demo%20Chap%2020.pdf) and it's only for one specific type of crank from one specific manufacturer. In the torque table for Race Face spline-fit cranks it says to torque them to 480 in-lbs for first installation and 420 in-lbs for reinstallation. But for everything else, including Race Face square-fit cranks, it just gives a range of torque values for each type to use for all installations.

As long as you have a 100% working torque tool, and you know how to apply it, then follow manufacturer's recommendation.

I have seen friends using a torque tool as if it was a cheater pipe, extremely scary.

The difference between 20 and 28 is a tab more, so it is not that much. That is why is better to take some items to a lbs, then again I have also seen mechanics who rarely use a torque tool and are excellent mechanics.

Is better to be safe than sorry.

I'd be a pretty confused OP at this point!

Operator, you seem to be saying that the torque required on reinstallation is less than that required on initial installation. If that's what your saying, please explain why.

Road Fan

Let me put it plainly - the torque is the same for every installation of a crank. That is the torque the crank is spec'ed to - this is usually around 35nm.

then again I have also seen mechanics who rarely use a torque tool and are excellent mechanics.

Is better to be safe than sorry.

Excellent mechanics know when a torque wrench is needed and when they are not. If you aren't predominantly working on high end carbon fibre parts/road bike then there won't be many cases where it is really *needed*.

Just ask sheldon brown.

Let me put it plainly - the torque is the same for every installation of a crank. That is the torque the crank is spec'ed to - this is usually around 35nm.

Thanks, that is clearer.

Excellent mechanics know when a torque wrench is needed and when they are not. If you aren't predominantly working on high end carbon fibre parts/road bike then there won't be many cases where it is really *needed*.

Just ask sheldon brown.

Not to invoke Sheldon when he's not here to be beaten up, please.

Capt. Bike never did seem to take into account that noobs have no idea what 35 Nm feels like or what it takes to apply it. He seemed more concerned with "bike repair for everyman" meaning as few special tools as possible.

To refute the idea that a torque wrench is only really needed "on high end carbon fibre parts", I invite you to count the number of posters here with square-taper cranks ruined because the bolt was under-torqued.

Not to invoke Sheldon when he's not here to be beaten up, please.

Capt. Bike never did seem to take into account that noobs have no idea what 35 Nm feels like or it takes to apply it. He seemed more concerned with "bike repair for everyman" meaning as few special tools as possible.

To refute the idea that a torque wrench is only really needed "on high end carbon fibre parts", I invite you to count the number of posters here with square-taper cranks ruined because the bolt was under-torqued.

Oh trust me, the "torque wrench" is not needed applied to experienced mechanics only. If you are starting out and have no idea what proper torque feels like, then you learn it by using one and by experience.

I have no idea what 35 nM feels like and have installed many cranks. None have fallen off.

Obviously 35 Nm is "tight enough" to you. Doesn't matter what you call it, it's the same tightness.

Now try to convey that to a noob without resorting to trial and error - or arm wrestling.


(And yes, operator, I agree. But the "noob" argument is less subject to ..er.. subjectivity.) ;)

If there not needed,why do they make them!You can make a guess,but that's all it is.And people wonder why their cranks fall off and why square tapers get bigger over time.35lbs of torque will not broach a forged aluminum crank arm.

Has anyone experienced an properly torqued assembly fail due to the torque spec? Why take a chance? The metric of success is not "none have fallen off" (under torqued). Look, we dealing with dissimilar materials and different size fasteners. Only a mechanic who has years of experience and calibrates himself once in awhile can be trusted with properly assembling any fastener. The risk of not using proper torque either way, is damage either immediate or over time due to stress.

BTW, did you know when lubricating a faster you should cut the torque value to as much as 50%?

oh my gosh---- torque till your eyes turn blue---- I would never use a torque wrench on a bicycle---
bolts with cheap threads and soft nuts and frames with sloppy taps--- Material ranging from
Manganese to titanium to various grades of aluminum and steel--- all put together en mass with
5 colors of loctite--- ya, you guys are missing the big picture--- show me a bicycle with chevy heads and a leaking water pump...... and I'lll stop drinking..............................

Ready to stop huh:

http://tbn0.google.com/images?q=tbn:e15dQbm4C6oJ::www.alumrad.com/BossHossRad.JPG (http://www.google.com/imgres?imgurl=http://www.alumrad.com/BossHossRad.JPG&imgrefurl=http://www.alumrad.com/gallery.htm&h=427&w=640&sz=68&tbnid=e15dQbm4C6oJ::&tbnh=91&tbnw=137&prev=/images%3Fq%3Dboss%2Bhoss&hl=en&usg=__UEy9o7HqRHTXs85oS_iDpf_PImU=&sa=X&oi=image_result&resnum=7&ct=image&cd=1)


There you go....have fun at AA meetings.....

Ready to stop huh:

http://www.daytonabosshoss.com/showroom2t.jpg (http://www.daytonabosshoss.com/showroom2.jpg)

There you go....have fun at AA meetings.....

stop... thats your dads old plastic model motorcycle collection... urp........ya....zz, urp.

None have fallen off is my metric of success. Not sure of a better one, as that is the goal as far as I can tell.

Opps,didn't think they made those,did ya? LOL!

How does one "suggest" torque--- when torque spec is a specific number?-- I love torque wrenches--- and I would suggest anyone get to know how to use one-- but on an old bicycle?

Bicycle torque specs often are a range of numbers rather than a specific number. The reference books I checked gave ranges for some cranks and specific numbers for others. One book recommended (or "suggested") an approximate value of 350 in-lbs for cranks that didn't have manufacturer's specs available, so that's what I used on my old bike.

ok, for all you gearheads that work on MOTOR cycles and cars---- use a gd torque wrench......
If your not strong enough to torque down a 14mm crank bolt with a simple ratchet----
I can see a manuf. setting specs for a carbon isis crank-- great
but, come on, anybody who works on custom projects has no Idea what the spec is-- the variation is too much-- the trial and error in setting your own values is worthless to me,( dead dog time).

Ya know-- torque setting is not always about how "tight" but
"just right" for the tolarance of the part!-- forget about the thing falling off or creeking-- think about it failing under load or heat--- when you torque to spec-
gen its to uniformly seal...........

o..... and I'lll stop drinking..............................

I rather doubt it.

:innocent:

..but, come on, anybody who works on custom projects has no Idea what the spec is-- the variation is too much-- the trial and error in setting your own values is worthless to me,( dead dog time).

Ya know-- torque setting is not always about how "tight" but
"just right" for the tolarance of the part!-- ....

You don't understand how a threaded fastener works. The threading *stretches* the fastener so that - like a spring - it applies force on the clamped parts. The amount of clamping force is determine by the designer when he specifies the fastener. The torque value is that required by the fastener to stretch some, but not too much. Accordingly, most torque specs can be determined simply by looking up the size and material of the fastener.

I say "most" because there are some applications where the safe clamping force isn't limited only by the fastener. Seat post and stem clamps apply radial pressure to the post and stem, and the torque range of the fastener might be greater than the part can handle. But for something like a crank bolt the parts being clamped are irrelevant.

If you want to really muddy the water ,we can include "torque-to-yield" fasteners.

A torque wrench is really a way of setting bolt stretch.That's why there are different torque settings for the same bolt,if it is dry,with different types of lubes,threads are clean,that kind of stuff.The correct way to tighten a bolt is by a given amount of stretch,but a "torque wrench" that measures stretch is LOTS of money.Those are not needed unless you have some big money on the line,think space shuttle.They use an inducer to measure the lenght of the fastener.I have one I use at work but it's used mainly for design and prototype work,not for production.

Oh that's interesting. I wondered how they did that on blind bolts. I can hear the dollar signs from here.


Please, let's just forget about torque-to-yield. :innocent:

Yeah, torque-to-yield is a very specialized application. It primarily started out in the automotive industry to lower costs, weight and add more options in cylinder-head designs. Tell-tale signs are specs. in torque-angles rather than regular torque ratings. I've seen these bolts with holes in them to measure the stretch without having access to the back side. TTY bolts also cannot be re-used.

No, we don't have to worry about TTY bolts on bikes. :)

No, we don't have to worry about TTY bolts on bikes. :)

I'd say most bike fasteners tightened to no where their near maximum torques values.

No properly specified or installed fastener is. But over-torquing is probably more prevalent on bicycles than under-torquing simply because the fasteners are relatively small.

We use the example of the crank bolt because it generates so much traffic here (the cause being non-obvious from the effect).