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  1. #1
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    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.

  2. #2
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    Quote Originally Posted by gutsofgold View Post
    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.
    Last edited by elTwitcho; 03-25-09 at 10:36 AM.
    Rich

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    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/cpis...ench&Submit=Go

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

  5. #5
    Senior Member pyroguy_3's Avatar
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    Quote Originally Posted by elTwitcho View Post
    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?
    Erwin Schroedinger will kill you like a cat in a box. Maybe.

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    Quote Originally Posted by pyroguy_3 View Post
    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.
    Rich

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    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?

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    Senior Member pyroguy_3's Avatar
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    Quote Originally Posted by gutsofgold View Post
    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.
    Erwin Schroedinger will kill you like a cat in a box. Maybe.

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

  10. #10
    Senior Member tmh657's Avatar
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    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.

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    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.

  12. #12
    Senior Member pyroguy_3's Avatar
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    Quote Originally Posted by tmh657 View Post
    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.
    Erwin Schroedinger will kill you like a cat in a box. Maybe.

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    Quote Originally Posted by pyroguy_3 View Post
    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.
    Rich

  14. #14
    Senior Member pyroguy_3's Avatar
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    Quote Originally Posted by elTwitcho View Post
    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.
    Erwin Schroedinger will kill you like a cat in a box. Maybe.

  15. #15
    partly metal, partly real sp00ki's Avatar
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    Quote Originally Posted by elTwitcho View Post
    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...
    Quote Originally Posted by bonechilling View Post
    Road [racing] is one of the only sports where adult men can compete in a non-scholastic setting, so inevitably 8/10 racers are fiercely-competitive nobodies. It's fun as hell, but it's also the foremost refuge of defeated and aging jocks, turned middle-management types.

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    Lurker yoyosup's Avatar
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    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.

  17. #17
    partly metal, partly real sp00ki's Avatar
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    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.
    Quote Originally Posted by bonechilling View Post
    Road [racing] is one of the only sports where adult men can compete in a non-scholastic setting, so inevitably 8/10 racers are fiercely-competitive nobodies. It's fun as hell, but it's also the foremost refuge of defeated and aging jocks, turned middle-management types.

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    Senior Member bigvegan's Avatar
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    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.

  19. #19
    Senior Member lukewall's Avatar
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    Quote Originally Posted by bigvegan View Post
    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.
    Quote Originally Posted by Jabba Degrassi View Post
    And I can't help but lol at the "heavier-set" riders I see on the trails riding around on $5000 speed machines. Nothing funnier than someone paying $4000 to shave 5 lbs when they're packing an extra 50...

  20. #20
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    One of the biggest mistakes I have noticed through the years is the misunderstanding of two different metals forced to be together. Take the tapered cranks for instance. The correct torque used on the first assembly is a big deal. I have been restoring bicycle for many year now there is a big difference between a parts changer and a mechanic.

    On new alloy cranks to a steel tapper spindle it is paramount you do it correct the first time. make sure you free ball to get that 50 to 75 years of use out of it.
    well any way the aluminum cranks stretch when placing them on and this is what they are suppose to do. And blue loc-tite is a must. I never lubricate the tapper.
    You want the electrolysis to happen. That is aluminum oxide and it will swell the crank and actually make a better fit.
    remember we are building this for customers and want them to last. if it is hard getting them off 10 years down the road take the bolt off hit it with oil. wait a day and then little heat with a torch and it will walk off.
    The main reason used crank installations fail is from the mechanic not letting the metal go back to shape. And the mechanic not marking the crank arm and spindle.
    Remember it has changed the moment you put 500 pounds of muscle pushing down on it.
    I like to put my cranks in the freezer. Yes in the freezer and my spindle.this makes my aluminum stiffer and it makes my spindle smaller. "Or wait 8 hours" This allows the alloy crank to shrink back.
    The fact is that crank is not a virgin and will never be the same. It is up to you to look at it as your putting it on make sure you get at least 26 nm on them. the aluminum will warm up faster than the steel spindle slowly it will all meld together. This has never let me down after learning it from another old time bicycle mechanic.
    Trust me you do not want to ruin a old set of TA cranks they are hard to replace. As far as old steel cranks the number one reason is the mechanic did no lube them put them on vibrate them with a drift then re torque them ride it then re torque .

    as far as today's truvative or shimano type that use a bolt not a nut. It's the splines on the cartridge bottom bracket get ruined they made them this way sorry guys. I have a old suntour cartage bottom brackets that still going down the road. the threads on the newer cartridge get stressed out. you should run a tap down them clean them up then and new bolts loc-tite.
    if you look at the newest cranks sets out today they look like what we had from the 1800's slide through and tighten one side up. yes they like to think it is new. fact is it is easier to assemble.
    if you read all this thank you old timer
    Flats Fixed.

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  22. #22
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    Quote Originally Posted by bigvegan View Post
    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.
    Actually if you have to tighten them after installation it to late the damage is done. steel against aluminum the aluminum is ruined or the splines on in the cartridge have been stretched out.
    you may get lucky on a tapper crank like I did on my old motobecame vitus tubing supper touring able to feel it get loose take the arm off clean it up loc-tite the nut on.
    a fixie does not make a defference ok a fit is a fit, if it came loose you did something wrong or it was already damaged prior to installation. I really do not want to go into the actual physics of why your statement should be reconsidered
    but it simple physics. What you want is a one peace forged crank arm for the chain ring side Right side. The pressed fit ones will work loose Chain ring not the crank arm. not always but I have seen it.
    As far as needing a torque wrench that's the difference between a mechanic and a parts changer. And understanding torquing a used crank 35 nm factory standard may ruin it.
    If the crank set comes loose something was wrong with the installation. if chain rings come loose measure the bolts I get the shorties in that are .25 mm to long and I have to grind them down. very common on that big name fixie company.

    as far as stress trust me the only thing that gets tweaked is the frame nothing like old steel.
    FlatsFixed

  23. #23
    pro in someone's theory prooftheory's Avatar
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    Quote Originally Posted by FlatsFixed View Post
    One of the biggest mistakes I have noticed through the years is the misunderstanding of two different metals forced to be together..
    One of the biggest mistakes I've noticed through the years is not recognizing that thread is 5 years old and that no one is likely to read what you say and find anything valuable in it.
    Last edited by prooftheory; 07-08-14 at 03:36 PM.

  24. #24
    Senior Member hockeyteeth's Avatar
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    Quote Originally Posted by FlatsFixed View Post
    Put your Hollowtech II cranksets in the garbage and/or freezer and admit Shimano stole that tech from 1800s farriers.
    Wow. That was one of the craziest fulminations I have ever read on this site.

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    Rockwell hardness

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