Singlespeed & Fixed Gear - Crank arms and torque

Do most of you just judge the torque on the crank arms bolts when installing? Or do you actually use a torque wrench? I hand tightened mine and then gave each one an extra "push" so I could feel the crank arms squeeze up on the BB spindle. I've rode it a few times and it feels great, I'm just not sure if it's too tight (ruin the crank arms?) or too loose.

Do most of you just judge the torque on the crank arms bolts when installing? Or do you actually use a torque wrench? I hand tightened mine and then gave each one an extra "push" so I could feel the crank arms squeeze up on the BB spindle. I've rode it a few times and it feels great, I'm just not sure if it's too tight (ruin the crank arms?) or too loose.

Not only can too tight ruin the crank arms, but too loose will ruin the crank arms. So can re-tightening the crank arms after they're already installed.

This is why a torque wrench is a good idea. A 20 dollar tool can save you from ruining a couple hundred dollars in cranks. You can get by without one on cheap cranks (I installed a 50 dollar set of cranks without a torque wrench because I didn't mind if I messed em up) if you just tighten them down really well. It's a lot more common to have them too loose than too tight.

Easy enough. I'm looking on tool sites for the appropriate one. I'm guessing I'll need an adapter that lets me use the 8mm allen wrench tip needed for the Sugino crank bolts. Could somepoint me in the right direction?

I'm guessing one of these + an adapter?

http://search.harborfreight.com/cpisearch/web/search.do?keyword=torque+wrench&Submit=Go

Yeah. Pretty much any torque wrench rated to the appropriate torque will work.

Not only can too tight ruin the crank arms, but too loose will ruin the crank arms. So can re-tightening the crank arms after they're already installed.

This is why a torque wrench is a good idea. A 20 dollar tool can save you from ruining a couple hundred dollars in cranks. You can get by without one on cheap cranks (I installed a 50 dollar set of cranks without a torque wrench because I didn't mind if I messed em up) if you just tighten them down really well. It's a lot more common to have them too loose than too tight.

Could somebody explain how overtightening can ruin the arms? Can it deform the metal? Or is it more a matter of stripping out the spindle?

Could somebody explain how overtightening can ruin the arms? Can it deform the metal? Or is it more a matter of stripping out the spindle?

It can cause the crank itself to crack at the taper. Like this

http://pardo.net/pardo/bike/pic/fail/FAIL-005.html

You'd have to put a lot of torque into tightening it, but it's not totally uncommon.

Do I need a 1/4 or 3/8? And where would one get the right adapter to go from socket wrench to allen head?

Do I need a 1/4 or 3/8? And where would one get the right adapter to go from socket wrench to allen head?

The adapter can be found at any hardware store most likely. I know for a fact Sears has them. Ace, Home depot, places that cater to automotive tools would def. have them.

The 1/4 or 3/8 thing, do you mean the driver (the square part the sockets fit on)? In that case, 3/8 is THE standard for the sizes of sockets you will find that need to be used on a bike. If you're referring to something else, then... I don't know.

i tightened the cranks on using a short wrench with some gusto. i think im going to go loosen them now.

I have DA w/Octalink so I don't stress it but>>>>

I posted a question on another forum re: torque wrench and it seems that the 1/2 of the people that don't own one say you don't need it and the 1/2 that do own it say you can't do without it so..

YMMV seems to be the norm and tighten w/ caution.

ive never used torque wrench and never had a problem. if i worked in a shop i would, as i have the respocibility of other people bikes and money on my head. but otherwise just do it up real tight, but to the point where i know there is still a little more i could give it if i put all my weight on it.

I have DA w/Octalink so I don't stress it but>>>>

I posted a question on another forum re: torque wrench and it seems that the 1/2 of the people that don't own one say you don't need it and the 1/2 that do own it say you can't do without it so..

YMMV seems to be the norm and tighten w/ caution.

I have one, and use it on occasion. The only times I ever use it are when I install my mtb's bb or cranks. The cranks on my fg are steel, so I'm not as worried about stress cracking them as with my aluminum ones. It's good to have if you do a lot of service on your bike, i.e. removing cranks often for travel etc, so that you don't repeatedly over tighten, but you don't need one if you just use common sense. For instance, you don't simply finger tighten the bolt that holds your cranks on, but you also don't jump up and down on the wrench trying to get it as tight as humanly possible. Use common-sense and you will be fine without one.

I also find that after installing a crank it's a good idea to check the crank arm bolt's tightness after a couple rides to make sure it didn't break loose.

I also find that after installing a crank it's a good idea to check the crank arm bolt's tightness after a couple rides to make sure it didn't break loose.

This is a lot more likely to ruin your cranks, don't do this. The bolt isn't breaking loose, the arms are settling on the taper. By re-tightening you're over-tightening the bolts.

From Jobst Brandt



Failure from "over-tightening" is caused by repeated re-tightening of properly installed cranks. In use, an aluminum crank squirms on its taper and, because the retaining bolt prevents it from moving off the taper, it elbows itself away from the bolt and up the taper ever so slightly. The resulting loss of preload, after hard riding, can be detected by how easily the bolt can be turned.

Loss of crank bolt preload is greater on left than the right cranks, because left cranks transmit torque and bending simultaneously while right cranks transmit these forces separately. The left crank transmits driving torque through the spindle to the right crank and chainwheel while the right crank drives the chainwheel directly. Besides that, the right crank transmits torque to the spindle only when standing on both pedals. Doing this with the right foot forward (goofy footed) is the only time the spindle transmits reverse torque.

Mechanics, unaware of why crank bolts lose preload (and commensurate crank tightening), have re-tightened bolts until cranks split. No warnings against re-tightening properly installed cranks are evident although it is here where the warning should be directed rather than at lubrication.

This is a lot more likely to ruin your cranks, don't do this. The bolt isn't breaking loose, the arms are settling on the taper. By re-tightening you're over-tightening the bolts.

From Jobst Brandt

That doesn't address what to do about "loss of bolt preload" though, lubrication of the threads maybe? I'll take my chances in cracking my crank, to forgo it rounding out and screwing me anyway.

It can cause the crank itself to crack at the taper. Like this

http://pardo.net/pardo/bike/pic/fail/FAIL-005.html

You'd have to put a lot of torque into tightening it, but it's not totally uncommon.

my friend CJ did that to a pair of records once. makes you wonder what campy was putting into its cranks...

This is a good reason to have a good relationship with your LBS. I took my cranks down to my LBS and they torqued it to spec for free. Better safe than sorry.

or you could buy a torque wrench... hands down, that + part research is your safest bet.

the guy i mentioned in the previous post worked at a shop, and is actually pretty experienced.

There's also a significant difference between tightening the cranks on a road bike and on a fixie, due to the different stresses involved.

If you're using a fixie on the street, you're going to be putting substantial pressure on the crank in both directions, so you're going to need to tighten the crank bolts a lot more often, especially if you're a heavier rider.

Don't crank them down so tight you split the crank, but do tighten them back up after every ride or two.

There's also a significant difference between tightening the cranks on a road bike and on a fixie, due to the different stresses involved.

If you're using a fixie on the street, you're going to be putting substantial pressure on the crank in both directions, so you're going to need to tighten the crank bolts a lot more often, especially if you're a heavier rider.

Don't crank them down so tight you split the crank, but do tighten them back up after every ride or two.

There's no difference between tightening cranks bolts on a roadie or a fg. Torquing the bolts to spec is the same no matter what type of bike.

Have you been paying attention how crank bolts are overtightened and split a crankarm? Just keep tightening up those crank bolts every few days, you're doing it right.