Left crankarm keeps loosening

Discussion in 'Mountain Bikes' started by MattLarson, Sep 12, 2004.

  1. MattLarson

    MattLarson New Member

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    My left crankarm and I are about to go to war.

    When I ride a couple miles, the left crankarm bolt starts to back out and the crank gets wobbly.

    The ride in question is a Giant Rainier (2003) with Truvativ cranks, and a taper style BB.

    I have tried blue loctite, and so has the LBS wrench. It gets annoying as all get out to ride a couple miles, stop, tighten the crank and go again.

    Any ideas out there?

    Matt
     
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  2. closesupport

    closesupport Banned

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    I HAVE HAD A SIMILAR PROBLEM WITH AN OLD HYPERDRIVE, THE PROBLEM ORIGINATED FROM A PERIOD OF TIME THAT I HADN'T TIGHTENED THE CRANK ARM UP, SO WHEN I WAS PEDALLING IT WAS ROCKING IN AND OUT, THIS CAUSED IT TO ROUND IN THE TAPER, THIS CAUSES THE CRANK ARM TO WORK LOOSE WHEN PEDALING, NOW YOU CAN EITHER TAKE IT OFF AND BEAT THE INSIDE (NEAREST TO THE FRAME SIDE) OF THE TAPER AND PUSH THE BARE BACK INTO PLACE THEN REPLACE, OR RENEW THE CRANK ARM.

    IF THAT DON'T WORK YOU WILL NEED TO REPLACE IT
     
  3. Mr_Kingkillaha

    Mr_Kingkillaha New Member

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    i had a crank arm fall comepletely off, and then i realized i didnt have the tools to put it back on. that was the most aggravating walk ive ever done.
    my problem was too many spacers, not enough clamping area. i dont know if that applies to yours tho.
     
  4. socalfeltrider

    socalfeltrider New Member

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    Unfortunately I think that you will need a new crank arm, like said above, the mating surface has been rounded out and the only solution is a new arm. Start fresh and check them periodicly (as tight as you can get it!)
     
  5. Juba

    Juba New Member

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    Mountain bike shops LUV people like yourself. Shops have the highest mark ups on replacement parts, and over-tightening parts is the third fastest way to wreck them (the first being wiping out, the second is using a high-pressure water hose to clean a bike).

    Tighten your crank bolts to the manufacturer's recomended torque. Square taper crankarms are one of the worst possible components to over-tighten. By over-tightening them, you are forcing the crankarm further up the spindle, which stretches the hole in the crankarm.

    Cheers,
    Juba
     
  6. closesupport

    closesupport Banned

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    try that with the bashing the bare on the rounded taper like i said! it does work once you have it beaten in properly, they don't work loose anymore.
     
  7. socalfeltrider

    socalfeltrider New Member

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    Hah Juba, that is quite funny and I just have to laugh. Just out of curiosity, what might the Manufacurer's recomended torque on a BB spindle nut or bolt be, AND how many bikes have you assembled and/or serviced in your time and (now think hard) how many times have you taken out your tiny torque wrench and used it????? If the answer is all the time or even most of the time I cannot imagine you were a very productive employee or even a usefull team mechanic in any arena because that is simply not protocol and honestly a waste of time!! I have assembled thousands of entry level IBD bikes, hundreds of pro-builds and countless hours as a technician for pro/semi-pro teams and I will tell you that you tighten them as tight as you can! NOW, saying that, i feel that no one would misconstrue "as tight as you can" by thinking you get a 250lbs muscle-head with a 4-foot cheater bar to bear down on it, if you know how to turn a wrench then you can "feel" how tight is tight...
    Feel free to contact me directly with any questions on this since this is a public forum and I am in no way trying to mix words or start controversy here.
     
  8. socalfeltrider

    socalfeltrider New Member

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    And, not to add insult to injury, but mountain bike shops do "LUV" me as I have been a service manager at many, and have not "wrecked" anything as of yet, and in the last decade have yet to see a crank arm wrecked do to over tightening, I use my tools properly and teach my techs to do the same. In addition, if done correctly washing a bike with a hose is the "best" way to clean a bike, you have obviously never been in a mechanic's area after a muddy race, even at a road event all of us hose off the bikes...
     
  9. Juba

    Juba New Member

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    Oh I don't know, bike mechanic for 6 years. During the fall/winter months when we were building bikes full-bore, call it 8-12 assemblies a day 5 days a week. When we switched into the spring/summer months when we doing mostly servicing and tune ups, call it anywhere from 5-15 per day, 5 or 6 days a week, depending on the mechanical issues. Team mechanic for 2 of those years. Ran a home based bike service company for close to 10 years, where I have about 25 steady customers, that got tune ups or bought upgrades every couple months. If you feel like doing the math on that, go ahead because I don't feel like opening up my calculator at the moment.

    And, when I was a newbie tech, I was a chronic "tighten it as tight as I can" kind of guy, who tore my fair share of threads out. With that kind of practice, believe me, no one in the place could install a heli-coil faster then I. But, after the senior tech wrapped a wrench across my knuckles a few times, the torque wrench became my best friend until I was well versed with what proper torque felt like.

    And since you asked so nicely, Truvativ square taper crank bolts are to be tightened not to exceed 42N~m (31ft~lbf, 429kgf~cm).

    Cheers,
    Juba
     
  10. Juba

    Juba New Member

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    Guess we Canadians put a little more elbow grease into tightening things up, cause I have seen my fair share.

    In Canada, pretty much all we have are muddy races. And I said high-pressure hose, like the kind you find in car washes. And if you are trying to argue that a high-pressure hose does not destroy bearings, well I am afraid I will have to let you live in your own fantasy world, as nothing I could possibly say on a message board could bring you back to reality.

    Cheers,
    Juba
     
  11. socalfeltrider

    socalfeltrider New Member

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    Well then Juba, I stand corrected, because in your (I did the math) 7500 bike builds and over 6000 serviced bikes I guess we have all learned that you "Canadians" are "too strong for your tools, and carelees with the aim of your hoses".
     
  12. Juba

    Juba New Member

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    We could go on bickering all day, care for a truce socalfeltrider?

    It is just I am leary of making the assumption that people always have common sense. No way to tell if the guy on the other side of the monitor is a 250lbs gorilla with a 4' cheater bar in his sweaty hands. I mean, when I say "as tight as you can get it" to my father, he instantly whips out his pneumatic impact wrench and smiles.

    Reminds me of the first time I got burned by assuming other people had common sense. Guy that phoned me up and asked if a Mavic 222 rim and 1.8mm spokes would build a good wheel for light duty XC, I said sure would. Guy came into the shop a couple weeks later, tacoed wheel in hand screaming at me. If the guy weighed a pound less then 325, I would have been amazed. I was about to say something along the lines of "don't you think it would have been common sense to mention that you were a wee bit horizontally challanged?" I mean, I was happy the guy was getting into mountain biking, but come on.

    Cheers,
    Juba
     
  13. socalfeltrider

    socalfeltrider New Member

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    A truce would be great.
    Bickering back and forth (especially online) is pointless and was certainly not my intention here. sharing ideas and knowledge is how we all learn, and after reading through some of your other posts, I have no doubt that you know what you are talking about (I ride and work on dirt bikes as well and I read your post about suspension sag and you are right on the money). I may have jumped the gun a bit in thinking that things that seem simple, and are common sense to someone who has experience, may be confusing or misleading to others. All of my posts are only meant to help. I will continue to try to do that, but thanks for pointing out that it may not be the best idea to assume that everyone has skill or experience, and that some are new to this.
     
  14. closesupport

    closesupport Banned

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    no but it does reck decals, you gotta admit that, to really a presure wash is okey, if your bike has no decals i have 2 sets of suspension forks that the decals have been ruined by jet or high pressure hoses.

    but my mtb no longer has them and i can use them whenever, but when it comes to my road or TT then there is nothing like the loving care and time that i spend cleaning them, with soap and water, use of a nice soft tooth brush to get into those hard to reach areas, dry to get rid of the dirt, then whipe down with mr muscle degreeser whipes, polish silver areas, then apply a thin layer of vaseline to silver areas after oiling moving mechanical parts.
     
  15. tyler_derden

    tyler_derden New Member

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    Are you sure you have tightened the bolts properly? Crank bolts require a lot of muscle to tighten properly- look at the park tools site for typical crank bolt torque specs. Use a torque wrench to tighten it to proper tension and it should stay put.

    I got a used bike and the girl I got it from told me that the crank bolts needed periodic tightening. Stange, I thought. I later figured out that the BB was not original equipment, but was a little shorter, so torqueing the crank bolts properly made the cranks hit the chain stay on the left side of the bike. I found this out -you guessed it- when I used a torque wrench to properly tighten the bolts.

    TD
     
  16. closesupport

    closesupport Banned

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    OKEY! Like i stated earlier, only you know if at any period of time before it started happeing had you had your crank arm off! if so then tere is a great possibility that you didn't tighten it adequately and it has rounded the inside of the taper on the flat edge.

    if you pull and push at the crank you will undertsand where i mean, this now rocking motion; that the crank arm has now got the ability to do is what causes the crank arm to work loose.
     
  17. King Fisher

    King Fisher New Member

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    I am not so sure about the tight as you can get it method because if you have a crank bolt that is tighter than 30 footpounds it may break off making your bottombracket next to impossible to repair without an extractor set:eek: I only know this because I had to extract a broken bolt from an almost new totally awesome shimano taper spindle BB:mad: It took hours!:mad:

    King Fisher
     
  18. Leon

    Leon New Member

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    I have had the same problem but with a race face splined crank. Today during a two hour bike ride I had to tighten it four times.
    From what I have read I need a new crank ?
     
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