Do I really need a torque wrench for cranks and BB?

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Do I really need a torque wrench for cranks and BB?

Postby adaml » Fri Jan 11, 2013 2:15 pm

As the title says, I'm going to install a UN55 square taper bottom bracket and Alivio crank into an alloy MTB frame. Is a torque wrench really necessary? I was thinking of torquing the crank bolts by using a cheater bar and pushing it hard and the BB itself by using the cheater bar and whaling on it.
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by BNA » Fri Jan 11, 2013 2:29 pm

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Re: Do I really need a torque wrench for cranks and BB?

Postby il padrone » Fri Jan 11, 2013 2:29 pm

No.

Try not to overdue it with extender bars. Good solid pressure on a conventional wrench or 12" shifter should be more than enough.
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Re: Do I really need a torque wrench for cranks and BB?

Postby mitzikatzi » Fri Jan 11, 2013 2:44 pm

As mentioned the bottom bracket needs to be snug not super tight. I would not be "whaling on it".

The "crank bolts". I have a 8mm allen key about 200mm long. I read somewhere that this will only allow about the correct torque to be applied (provided you don't go silly). Again don't "whale" on it. You can force the soft alloy arms onto the steel shaft of the bottom bracket. Check the bolts after a couple of short rides.

If you don't know how to do bolts up by feel you might be better off with a torque wrench.

Some say do not apply any "lube" to the shaft before installing the crank arms.
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Re: Do I really need a torque wrench for cranks and BB?

Postby il padrone » Fri Jan 11, 2013 2:47 pm

I always lube my tapir :lol:

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Re: Do I really need a torque wrench for cranks and BB?

Postby rustychisel » Fri Jan 11, 2013 4:46 pm

that is a mighty fine tapir, sir, and I agree.
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Re: Do I really need a torque wrench for cranks and BB?

Postby Mustang » Fri Jan 11, 2013 5:06 pm

INVEST in all the tools you need, its a lot more satisfying knowing you have done the best job you can. I enjoy looking at my growing tool box, it must have saved me heaps.
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Re: Do I really need a torque wrench for cranks and BB?

Postby grantw » Fri Jan 11, 2013 6:09 pm

Yes, the right tool for the job is always better. I find with most bike tools you only have to use them once or twice before they have paid for themselves in shop fees or "oops" parts that you have to replace.
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Re: Do I really need a torque wrench for cranks and BB?

Postby il padrone » Fri Jan 11, 2013 6:21 pm

Been working on my own bikes for over 30 years. I have lots of specific bike tools. But I've never owned or used a torque wrench. All my bikes are steel or alloy... no carbon. Have not had any 'oops' moment for many a long year.

Before the advent of mass-market carbon frames and parts, torque wrenches were virtually unheard of.
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Re: Do I really need a torque wrench for cranks and BB?

Postby grantw » Fri Jan 11, 2013 8:50 pm

I kinda got the feeling from the OP that the original premise was:-

torque wrench = more leverage
therefore substitute long piece of pipe on wrench + heave as hard as I can to fit BB

as opposed to

torque wrench = specified torque applied.

Right tool for the job = win :)
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Re: Do I really need a torque wrench for cranks and BB?

Postby wqlava1 » Fri Jan 11, 2013 8:52 pm

il padrone wrote:Been working on my own bikes for over 30 years. I have lots of specific bike tools. But I've never owned or used a torque wrench. All my bikes are steel or alloy... no carbon. Have not had any 'oops' moment for many a long year.

Before the advent of mass-market carbon frames and parts, torque wrenches were virtually unheard of.

As someone who has had a $15 K-Mart 0-150lb torque wrench for 34 years for my early cars, and a theoretically better Warren & Brown 0-80lb clicker for 30 years for my motorbike, I naturally look out for the right torques and they are there and have been specified. My deeper interest in bikes has only been the last 7-8 years, but I have readily found sources of the cassette, BB and crank torques (the only ones that I have really needed to use regularly). For example in Barnett's manual, an early version of which I found years ago scanned on some Russian site.

Those 3 are all around 30-40 ft/lb, which is a comfortable pull but by no means needs any cheater bar for people of normal strength with common tools. A 200mm allen key on your crank bolts needs just about 30kg assuming that you will only be able to get the force applied a cm or 2 from the end - which is quite likely at the limit of comfort! A long handle exerting pressure on a plastic BB end nut may well strip it (and the lightweight metal for the UN55 BB is not noticeably stronger than the plastic they had for the UN54), and likewise if you ever tighten the weak-looking lockring on an aluminium freehub, you wonder which one would strip first (I do, anyway).

But if you just pull on all 3 pretty firmly and have worked out what about 30-40lb/ft feels like, you will probably be fine.....
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Re: Do I really need a torque wrench for cranks and BB?

Postby Mulger bill » Fri Jan 11, 2013 9:53 pm

I don't use a torque wrench on pedals, crank tapers or BBs, I just tighten to snug then add a fraction more, never had a problem.

Isn't the handedness of BB and pedal threads that way for a reason?
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Re: Do I really need a torque wrench for cranks and BB?

Postby wqlava1 » Fri Jan 11, 2013 10:15 pm

Mulger bill wrote:I don't use a torque wrench on pedals, crank tapers or BBs, I just tighten to snug then add a fraction more, never had a problem.

Isn't the handedness of BB and pedal threads that way for a reason?



I think the handedness is for safety, to avoid them self-undoing when the older type BBs with loose bearings run out of lubricant and lock up, and the rider keeps pedalling.
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Re: Do I really need a torque wrench for cranks and BB?

Postby RonK » Fri Jan 11, 2013 10:43 pm

It's a balancing act with bb's - you don't want over tighten them, but if they are not tight enough they may creak or click.

Much more important with the UN55 is the sequence of assembly and tightening. You need to screw in the bb nearly all the way home, then start the left side cup, return and fully tighten the right side, then the left side. Use plenty of grease.

BTW, if you don't like the plastic left side nut, you can buy an aluminium replacement. Just make sure you order the correct size according to the bb shell width.
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Re: Do I really need a torque wrench for cranks and BB?

Postby ball bearing » Sat Jan 12, 2013 9:41 am

I reckon that a torque wrench is an essential tool for bikes, especially if you work on dual suspensions. The torque values are critical when doing up the swing arms. I also use my torque wrenches on my carbon road bike. As for the BB, if you have ever tried to remove a BB that has been over-tightened you will understand how valuable a torque wrench is. Damaged BB shell threads are enough to make a grown man cry.

I think that most bike mechanics who insist that their tighten-up and back off a bit is good enough is anywhere near accurate would be surprised how far off their bush-mechanic skills are when it comes to proper torque of components.

I have four torque wrenches going from my tiny Warren & Brown one to my big Snap-on.
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Re: Do I really need a torque wrench for cranks and BB?

Postby Mulger bill » Sat Jan 12, 2013 9:52 am

ball bearing wrote:I reckon that a torque wrench is an essential tool for bikes, especially if you work on dual suspensions.

Absolutely. The main reason I got mine tho' it has paid for itself over most of the rest of the fleet too.
Still not sure whether it's needed for cassette lockrings... :?
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Re: Do I really need a torque wrench for cranks and BB?

Postby ball bearing » Sat Jan 12, 2013 9:56 am

Mulger bill wrote:
ball bearing wrote:Still not sure whether it's needed for cassette lockrings... :?


I guess it is a individual thing - I find that doing up the lockring to 40Nm is usually the only surefire way of eliminating play and saving the hub threads at the same time.
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Re: Do I really need a torque wrench for cranks and BB?

Postby rkelsen » Sat Jan 12, 2013 10:38 am

RonK wrote:BTW, if you don't like the plastic left side nut, you can buy an aluminium replacement.

That's flippin' awesome! The plastic LH cup always looks a bit off, and they're too easy to strip as well. This is going straight to the pool room... or maybe my just Bookmarks list... 8)
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Re: Do I really need a torque wrench for cranks and BB?

Postby il padrone » Sat Jan 12, 2013 6:52 pm

ball bearing wrote:I reckon that a torque wrench is an essential tool for bikes, especially if you work on dual suspensions.

OP said nothing about his dual suspension requirements :|
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Re: Do I really need a torque wrench for cranks and BB?

Postby ball bearing » Sat Jan 12, 2013 9:05 pm

il padrone wrote:
ball bearing wrote:I reckon that a torque wrench is an essential tool for bikes, especially if you work on dual suspensions.

OP said nothing about his dual suspension requirements :|


Says he who never owned or used a torque wrench. ; )

Doesn't hurt anything to have the right tool - and if you have it you might as well use it on the BB and other assorted bits. Hell, I even know people who think a workstand is an unnecessary tool and they hang their bikes from an old inner tube. Hey, if it works it works - I know how I like to do things, I'm happy that you know what works for you.
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Re: Do I really need a torque wrench for cranks and BB?

Postby wqlava1 » Sat Jan 12, 2013 9:28 pm

rkelsen wrote:
RonK wrote:BTW, if you don't like the plastic left side nut, you can buy an aluminium replacement.

That's flippin' awesome! The plastic LH cup always looks a bit off, and they're too easy to strip as well. This is going straight to the pool room... or maybe my just Bookmarks list... 8)

If you have a look at the price, its USD20 plus postage from the UK (must sell mostly to the US). I buy UN55 BBs from Bike24, usually once I have a need for a couple of hundred dollars' worth of stuff, for approx $18 or $19, with the 20 euros postage spread over all the items. It's not worth getting the aluminium one unless you will definitely be pulling the BB in and out on a regular basis, and even then you'd wait to see if you could save the supplied cup.

What usually wrecks a cup for me is when it has accumulated crap in the castellations/grooves of the cup and I don't take time to clean them out perfectly to let the tool seat fully, or when I don't position the frame optimally and use my best engaging tool on a comfortable long 1/2" drive extension so as to apply force exactly around the BB. Any angle on the tool is fatal for the cup.
Last edited by wqlava1 on Sat Jan 12, 2013 9:40 pm, edited 1 time in total.
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Re: Do I really need a torque wrench for cranks and BB?

Postby wqlava1 » Sat Jan 12, 2013 9:35 pm

il padrone wrote:
ball bearing wrote:I reckon that a torque wrench is an essential tool for bikes, especially if you work on dual suspensions.

OP said nothing about his dual suspension requirements :|


Yes, but this thread has been going a while, we have elicited a variety of flavours of good advice based on different experience, and it has wandered in a few related directions. I just think back a few days to a thread about a failed fork that I started. Early on, it got some good technical commentary (including from your good self), then the conversation broadened, whilst still staying vaguely related. It's how people are, and it's how the forum is commonly used, and maybe it's what some people find appealing.
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Re: Do I really need a torque wrench for cranks and BB?

Postby dontazame » Sat Jan 12, 2013 11:32 pm

I find that doing up the lockring to 40Nm is usually the only surefire way of eliminating play and saving the hub threads at the same time

I find 40nm for cassettes hard to guess (with the nm jump and using bigger tools) and its where using a torque wrench gives me the most peace of mind.
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Re: Do I really need a torque wrench for cranks and BB?

Postby il padrone » Sat Jan 12, 2013 11:49 pm

I'd say that during the 70s, 80s and for much of the 90s if you'd have walked into a LBS workshop you'd have been hard-pressed to find a torque wrench. I know there was no sign of any in the couple of shops I had some work in during this time, and none at the bicycle assembly line I worked with for a couple of years. We did have torque settings on the air-wrenches, but they were not used for BBs nor crank-bolts.
Last edited by il padrone on Sun Jan 13, 2013 10:43 am, edited 1 time in total.
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Re: Do I really need a torque wrench for cranks and BB?

Postby alex » Sun Jan 13, 2013 4:11 am

il padrone wrote:I'd say that during the 70s, 80s and for much of the 90s if you'd have walked into a LBS workshop you'd have been hard-pressed to find a torque wrench.


you wouldnt have found an EFTPOS terminal for much of that time in those shops either, guess they are useless too!
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Re: Do I really need a torque wrench for cranks and BB?

Postby il padrone » Sun Jan 13, 2013 8:18 am

Torque wrenches existed, but were not regarded as essential to being able to work on bikes.

Same could not be said for EFTPOS.
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