Forum home Road cycling forum Workshop

Crank thread stripped

nibnob21nibnob21 Posts: 207
edited December 2014 in Workshop
I bought a Cube Peloton Race the other day from CRC and took it out for the first time this morning.

I bought some Shimano R540 pedals to go with it as I've used them on my other bike with no issues. I screwed them in to the cranks as far as I could by hand and then gently tightened them up with an allen key. All looked good and they were fully screwed in.

I'd been happily cruising along for approx 7 miles when all of a sudden the left pedal felt offset. I quickly stopped and could see it was undone by a couple of turns or so. I thought it was a bit strange but easily tightened it back up by hand, as foolishly I had brought no tools with me. Just a hundred yards or so down the road it went funny again. censored , I thought, this isn't right. This time it was undone by less than before but wasn't budging by hand at all.

A couple of guys cycling passed stopped to help so we unscrewed the pedal with their tool to inspect. Pedal thread seemed ok, crank thread looked a bit suspect. We screwed the pedal back in gently on both sides and it was going in fine until just one or two threads were left when it wouldn't go in any further. At this point it became evident the crank arm thread had been stripped in places.

With the damage done and being 7 miles from home I had no choice but to do it back up and cycle gently home. I'm just wondering whether it's likely this is down to a defect with the original part as for 7 miles it was fine then it suddenly went.

Is it even possible to buy just the left crank arm (Shimano 105)?
Would I have a leg to stand on if I went back to CRC and requested a replacement left crank do you think, seeing as the bike is brand new?

Thanks.
«1

Posts

  • k-dogk-dog Posts: 1,652
    As you've said the problem is that you fitted the pedals - so the implication is that you crossed the threads a bit so ur worked loose.

    However CRC have a really good warranty procedure so it's worth contacting them. At the worst you can have it helicoiled at a good shop.

    Had almost the sane thing happen to me once - and I'm confident it was fitted properly - so it can happen that there is a flaw with the threads.

    LBS replaced the crank free of charge.
    I'm left handed, if that matters.
  • nibnob21nibnob21 Posts: 207
    k-dog wrote:
    As you've said the problem is that you fitted the pedals - so the implication is that you crossed the threads a bit so ur worked loose.

    However CRC have a really good warranty procedure so it's worth contacting them. At the worst you can have it helicoiled at a good shop.

    Had almost the sane thing happen to me once - and I'm confident it was fitted properly - so it can happen that there is a flaw with the threads.

    LBS replaced the crank free of charge.

    This is what I thought, with regards to the fact I fitted the pedals it doesn't exactly look good on me. I'm confident I fitted them correctly, backed up by the fact that for 7 miles with a mix of hard and gentle riding there were zero issues with the pedal.

    In the comfort of my home with my tools to hand I have managed to get the pedal back on straight and tight, but obviously the damage to the crank thread had already been done, so I'm not exactly full of confidence the same won't just happen again when I'm out on a ride.

    I'll contact CRC and see where that gets me. In terms of a brief search online it doesn't seem as though you can even buy the cranks separately, so I hope this doesn't end up costing me a fortune :(
  • imposter2.0imposter2.0 Posts: 11,387
    It won't cost a fortune - just take the crank arm to a decent machine shop and get a helicoil or timesert repair. Job done.
  • lesfirthlesfirth Posts: 1,207
    [quote="nibnob21

    I bought some Shimano R540 pedals to go with it as I've used them on my other bike with no issues. I screwed them in to the cranks as far as I could by hand and then gently tightened them up with an allen key. All looked good and they were fully screwed in.

    .[/quote]

    In my opinion the source of the problem is " gently tightened them up". You can not get sufficient tightening torque being gentle with an allen key. Worst case is a helicoil at a good LBS. No worries.
  • nibnob21nibnob21 Posts: 207
    lesfirth wrote:
    nibnob21 wrote:

    I bought some Shimano R540 pedals to go with it as I've used them on my other bike with no issues. I screwed them in to the cranks as far as I could by hand and then gently tightened them up with an allen key. All looked good and they were fully screwed in.

    .

    In my opinion the source of the problem is " gently tightened them up". You can not get sufficient tightening torque being gentle with an allen key. Worst case is a helicoil at a good LBS. No worries.

    Sorry for my mix up, allow me to rephrase. I gently screwed them in by hand first until they were fully in, then properly tightened them up with the allen key. I always use this method of 'hand first' then 'allen key at the end' to avoid cross threading; never had issues in the past.
  • k-dogk-dog Posts: 1,652
    He's still right though - you want a pedal wrench. You can't get enough leverage with an Allen key.
    I'm left handed, if that matters.
  • imposter2.0imposter2.0 Posts: 11,387
    k-dog wrote:
    He's still right though - you want a pedal wrench. You can't get enough leverage with an Allen key.

    Unless, of course, you have pedals (like Time, etc) which only have an allen key fitting. Pedals just need to be firmly nipped up into the cranks - they don't need to be wrenched 'gorilla-style'....
  • Monty DogMonty Dog Posts: 20,614
    This isn't a warranty claim issue because the user installed the pedals - it'll cost £10-15 at a bike shop to fix plus a valuable lesson for the future.
    Make mine an Italian, with Campagnolo on the side..
  • Manc33Manc33 Posts: 2,157
    How can a pedal thread that is going in stripped... get screwed in by hand?

    Either you have hands like Superman or you're not telling us something. :lol:
  • k-dogk-dog Posts: 1,652
    ^either there was something wrong with the thread or it wasn't tight enough then backed out slightly. Once it's get a little loose then it ruins the hole.
    I'm left handed, if that matters.
  • lesfirthlesfirth Posts: 1,207
    Imposter wrote:
    k-dog wrote:
    He's still right though - you want a pedal wrench. You can't get enough leverage with an Allen key.

    Unless, of course, you have pedals (like Time, etc) which only have an allen key fitting. Pedals just need to be firmly nipped up into the cranks - they don't need to be wrenched 'gorilla-style'....

    Shimano think they should be tightened to 35 to 55 newton meters. That is not "nipped up" in my book!
  • imposter2.0imposter2.0 Posts: 11,387
    Doesn't alter the fact that a lot of pedals don't have flats for wrench fitting....
  • lesfirthlesfirth Posts: 1,207
    Imposter wrote:
    Doesn't alter the fact that a lot of pedals don't have flats for wrench fitting....

    I am sorry I may be a bit dim but I fail to see the relevance of that statement.
  • imposter2.0imposter2.0 Posts: 11,387
    lesfirth wrote:
    Imposter wrote:
    Doesn't alter the fact that a lot of pedals don't have flats for wrench fitting....

    I am sorry I may be a bit dim but I fail to see the relevance of that statement.

    If you have another read of the thread, you will see that someone earlier said that an allen key was not sufficient to tighten the pedal threads and that a pedal spanner was needed. There are a few pedal manufacturers that appear to disagree with that - which was my original point.
  • keezxkeezx Posts: 1,316
    Another reason to stay with Shimano SPD SL pedals.
  • rafletcherrafletcher Posts: 1,235
    Keezx wrote:
    Another reason to stay with Shimano SPD SL pedals.

    What nonsense. For the record I've never torqued up a pedal (be it Look, SPD and SPD-SL, Time or Speedplay) - just tightened by hand. (In fact I've only ever torqued stuff that I fit to carbon frames, everything else I've judged myself) Then the fact that they have opposing threads (like "English" BB cups) means the action of pedalling keeps them tight. I've never had one come loose in the last 30 years.

    To the OP - it could be that there was dirt/swarf in the thread of the crank when you assembled the pedal - the crank threads are very soft and easily deformed. Take it to a bike shop and get them to chase out the thread with a tap first, and see if that works. If not then it'll need helicoiling or replacing.
  • keezxkeezx Posts: 1,316
    rafletcher wrote:
    Keezx wrote:
    Another reason to stay with Shimano SPD SL pedals.

    What nonsense. For the record I've never torqued up a pedal (be it Look, SPD and SPD-SL, Time or Speedplay) - just tightened by hand. (In fact I've only ever torqued stuff that I fit to carbon frames, everything else I've judged myself) Then the fact that they have opposing threads (like "English" BB cups) means the action of pedalling keeps them tight. I've never had one come loose in the last 30 years.

    Did I say something else? Don't even own a torque wrench,
    Nothing broke or came loose in 50 years.
  • crankycrankcrankycrank Posts: 1,830
    nibnob21 wrote:
    Is it even possible to buy just the left crank arm (Shimano 105)?
    Would I have a leg to stand on if I went back to CRC and requested a replacement left crank do you think, seeing as the bike is brand new?
    1st I'd take it back to CRC and see what they say. I wouldn't blame them if they refuse to replace the crankarm but you never know. If no luck just do as Imposter mentioned and have a thread insert installed. If done properly it will be stronger than the original alu threads. Also check the pedal threads very closely to make sure they're not damaged in any way before screwing into your new/repaired crankarm.
  • Monty DogMonty Dog Posts: 20,614
    The cost of sending crank back to CRC = tenner = same cost of getting a Helicoil fitted: Why bother?

    Loads of Allen key bit sets available with 3/8" or 1/2" square drive for plenty leverage - regular allen keys aren't suitable
    Make mine an Italian, with Campagnolo on the side..
  • imposter2.0imposter2.0 Posts: 11,387
    If you need extra leverage, just hang a ring spanner on the end of the allen key...
  • Manc33Manc33 Posts: 2,157
    Imposter is right, you can't get the leverage on a standard sized allen key.

    Just get a 3/8" square socket spanner and a set of hex sockets.

    http://www.its.co.uk/pd/AK656-Sealey-He ... wgodf3MAeQ

    I am getting a pair of pedals like this myself soon (if they ever get here, from you know where).

    Oh and don't sign up to anything on that ITS site, they spam you quite a bit and you can't unsubscribe - because Yahoo! thinks it is keeping you spam free by not allowing you to unsubscribe. :roll: Yep, its illegal to not put an unsubscribe link on emails from commercial websites, but it is all perfectly legal for your email provider to then stop you from unsubscribing. Its a conspiracy, but then what isn't. :twisted:
  • imposter2.0imposter2.0 Posts: 11,387
    Manc33 wrote:
    Imposter is right, you can't get the leverage on a standard sized allen key.

    I didn't say that.
  • Manc33Manc33 Posts: 2,157
    Imposter wrote:
    Manc33 wrote:
    Imposter is right, you can't get the leverage on a standard sized allen key.

    I didn't say that.

    It is what you meant - I merely clarified it for you.

    I think you probably must know it isn't possible to tighten a bolt up to 40 Nm by hand using only a 3" allen key.

    https://www.youtube.com/watch?v=rxfzm9dfqBw
  • imposter2.0imposter2.0 Posts: 11,387
    Manc33 wrote:
    Imposter wrote:
    Manc33 wrote:
    Imposter is right, you can't get the leverage on a standard sized allen key.

    I didn't say that.

    It is what you meant - I merely clarified it for you.

    I think you probably must know it isn't possible to tighten a bolt up to 40 Nm by hand using only a 3" allen key.

    https://www.youtube.com/watch?v=rxfzm9dfqBw

    As usual, you're not making any sense - don't presume to tell me what I meant. I'm not specifically recommending using a ring spanner - it's just another way of getting leverage on an allen key, if you need more force for any reason. I've always tightened my pedals into the threads fairly lightly - never lost one yet.
  • cyclecliniccycleclinic Posts: 6,865
    I also never torque up pedals. Just get then tight by hand with the spanner or allen key bit. They self tighen when pedalling so it works fine. Also apply anti seize to the threads.

    Any good shop will have the cyclus pedal thread destroyer/cutter. This destroys the old stripped thread and cuts a larger new threrad into which you screw in and loctite a bush which will accept you pedal. Tapping the existing threads is not a good fix if they have been stripped. If CRC do anything it is a good will guesture but I don't think it is fair on them seeing as it most likely your mistake. Learn the lesson suck it up and get it fixed. If your LBS does not have the cyclus tool then post the crank arm to a shop that does.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • lesfirthlesfirth Posts: 1,207
    There is something I do not understand on this topic.

    The OP has knackered a new crank. That is fact. The bit about dirt or swarf in the thread is b0ll0cks.

    Yes I know lots of you just nip up their pedals and have never had a problem but the OP has.

    Shimano recommend 35 to 55 newton meters. If you are experienced enough to guess that ok , you don't need a torque wench. In old money, which I understand, that is 25 to 40 foot pounds. You can not get that easily with a standard allen key. Certainly not being gentle! To do damage you would have to apply far more torque than that.

    If you tighten them to the recommended torque with a bit of copper slip on the threads removing them will never be a problem.

    What is advantage in "just nipping them up" or what is the down side to carrying out he manufacturers instructions.
  • Manc33Manc33 Posts: 2,157
    edited December 2014
    You'd need bones made from metal and flesh made from rubber.

    Imposter I wasn't talking about you saying to use a ring spanner, I was talking about you "not saying" you need more leverage when you did say that and it does need more leverage.

    Or just tighten them to 10-15Nm (whatever the limit is on your hand on a 3" long allen key without drawing blood) and hope they tighten up as you pedal. :roll:

    All the brochures, manuals and spec sheets seem to say around 40Nm which isn't even half what you can do by hand, not on a 3" long allen key anyway.
  • imposter2.0imposter2.0 Posts: 11,387
    lesfirth wrote:
    What is advantage in "just nipping them up"

    It's usually all that is needed - and rarely results in over-torquing.
    lesfirth wrote:
    or what is the down side to carrying out he manufacturers instructions.

    The downside is that most people who strip threads usually do it while using a torque wrench. No idea why. Well, I do, but it's a whole other thread...
  • cyclecliniccycleclinic Posts: 6,865
    nipping them up is around 35Nm. Once the pedal is inserted and it comes in contact with the crank thread nipping up is all that is needed to get to the required torque. Effort is not needed. Ever tried puting a BB in 40Nm is not alot and once the flange of the cup make contact with the frame alittle more of a turn at you at the required torque.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • Manc33Manc33 Posts: 2,157
    My BB went loose on its own after tightening it as tight as I could, of course Shimano thinks 1.5mm deep notches on the drive side cup are enough to stop the BB tool slipping for some inexplicable reason. If something like that is meant to tighten as you pedal (it is) then I don't know how it can come loose again but it managed to. Also why the splines are 3mm or 4mm on the non-drive side so you can tighten it really easily and its far more shallow on the other cup I have no idea. Maybe Shimano thinks we all have bench mounted metal vices, but that is the only way to get that shallow splined thing anywhere near tight.
Sign In or Register to comment.