tkD Posted October 5, 2009 Author Report Share Posted October 5, 2009 Get some better cranks? Seriously though. Left hand cranks have a tendancy to come loose. As soon as they come loose they start to splay the taper on the cranks (guessing you have square taper interface) ending up in a rounded taper over time.I'd first try a different bolt in, if you're struggling to tighten it properly try using a 14mm end bolt and tighten it up with a socket wrench, if you still find it comes loose, try some thread lock on the threads (or loctite if you want to get ripped off).If you've knackered the taper on the cranks already and you don't fancy buying any new cranks you can try cutting some old drink cans up into 4 peices and placing it on each flat and then trying the crank on. Or try some thread lock on the taper.When you say ripped off, you're implying that "loctite" would not be the best choice of thread locker? If you could give an example of another brand? At my work we have some industrial stuff we use for aluminium doors and stuff, would you imagine that is better? I only said loctite as an example of what I was considering using. The taper is still fine at the moment. Quote Link to comment Share on other sites More sharing options...
totaltrials Posted October 6, 2009 Report Share Posted October 6, 2009 Loctite is fine, I was just saying if you wanted to save some pennies get a cheaper brand of thread lock. Quote Link to comment Share on other sites More sharing options...
2sixstreet Posted October 6, 2009 Report Share Posted October 6, 2009 What size bolts are they and how much thread length is there on the bolt? A lot of BB designs don't have enough thread engagement to adequately secure the bolt no matter how tight you do them up. Without boring you with bolt theory, any bolt, regardless of length, will only engage a maximum of 3 threads. The bolt needs to elastically stretch in order for it to hold, therefore the longer the better. There is also friction between the head of the bolt and the mating surface which needs to be overcome before it can undo. It's a ratio thing so if you have a short stumpy bolt with a large dia then it's never going to stretch enough to hold. Over-tightening it will deform one, the other, or both parts and still undo.Some sort of thread lock will work for a while (I recommend stud lock). Ensure it cures for the recommended time before using.What I have done before is tighten as normal but leave the 8mm allen key in the head of the bolt and align it with the crank. Tape it around the crank in a couple of spots and it can't come undone. This only works with cranks shaped so they don't catch your feet. Quote Link to comment Share on other sites More sharing options...
tkD Posted October 6, 2009 Author Report Share Posted October 6, 2009 How quick do they come loose? Are you tightening them several times a ride for the first few rides?Well I didn't tighten them when I first got it (doh) they came loose after a couple of days, so I tightened it again a little bit, went riding came undone. This time I've just tightened the bollocks off it. I'll get some thread locker when I get money. Quote Link to comment Share on other sites More sharing options...
hoots man Posted October 6, 2009 Report Share Posted October 6, 2009 ISIS Quote Link to comment Share on other sites More sharing options...
tkD Posted October 6, 2009 Author Report Share Posted October 6, 2009 ISIS What do you mean? Quote Link to comment Share on other sites More sharing options...
Dan_Trials Posted October 6, 2009 Report Share Posted October 6, 2009 What size bolts are they and how much thread length is there on the bolt? A lot of BB designs don't have enough thread engagement to adequately secure the bolt no matter how tight you do them up. Without boring you with bolt theory, any bolt, regardless of length, will only engage a maximum of 3 threads. The bolt needs to elastically stretch in order for it to hold, therefore the longer the better. There is also friction between the head of the bolt and the mating surface which needs to be overcome before it can undo. It's a ratio thing so if you have a short stumpy bolt with a large dia then it's never going to stretch enough to hold. Over-tightening it will deform one, the other, or both parts and still undo.Some sort of thread lock will work for a while (I recommend stud lock). Ensure it cures for the recommended time before using.What I have done before is tighten as normal but leave the 8mm allen key in the head of the bolt and align it with the crank. Tape it around the crank in a couple of spots and it can't come undone. This only works with cranks shaped so they don't catch your feet.That's roughly along the lines of what I was getting at, only I was thinking more about the torsional rigidity of the steel versus the torque applied to it. Like I said, sorry to be so anal, but when you build rally cars untill 2am it kind of becomes inset What do you mean?ISIS is a form of bottom bracket and crank arm. Rather than a square taper it uses a splined axle and corresponding crank arm bore. Compare these to your bottom bracket. Quote Link to comment Share on other sites More sharing options...
tkD Posted October 6, 2009 Author Report Share Posted October 6, 2009 That's roughly along the lines of what I was getting at, only I was thinking more about the torsional rigidity of the steel versus the torque applied to it. Like I said, sorry to be so anal, but when you build rally cars untill 2am it kind of becomes inset ISIS is a form of bottom bracket and crank arm. Rather than a square taper it uses a splined axle and corresponding crank arm bore. Compare these to your bottom bracket.And these are better? Quote Link to comment Share on other sites More sharing options...
Dan_Trials Posted October 7, 2009 Report Share Posted October 7, 2009 And these are better?Yes, most would agree. If you are thinking of going to ISIS you would also need cranks to suit. Quote Link to comment Share on other sites More sharing options...
tkD Posted October 7, 2009 Author Report Share Posted October 7, 2009 Yes, most would agree. If you are thinking of going to ISIS you would also need cranks to suit.How are they better? And eurgh, more money, already paid stupid amount for the bike Quote Link to comment Share on other sites More sharing options...
2sixstreet Posted October 7, 2009 Report Share Posted October 7, 2009 That's roughly along the lines of what I was getting at, only I was thinking more about the torsional rigidity of the steel versus the torque applied to it. Like I said, sorry to be so anal, but when you build rally cars untill 2am it kind of becomes inset ISIS is a form of bottom bracket and crank arm. Rather than a square taper it uses a splined axle and corresponding crank arm bore. Compare these to your bottom bracket.Did you mention anything about bolt theory? Must have missed it....Torsional rigidity has sweet FA to do with the bolt in this case. It's not anchored and your not trying to twist it. Isis is a better system for dummies I agree as it isn't as easy to deform the engaging faces from misuse etc but the bolt design is worse than tapered designs. Quote Link to comment Share on other sites More sharing options...
3001978 Posted October 7, 2009 Report Share Posted October 7, 2009 (edited) It has been mentioned, but to reiterate it sounds like you have started to round the taper on the crank (mostly happens with the left hand crank arm and on square taper cranks) Once you noticed that it was loose I presume there was a small amount of riding involved (i.e to get home / pub / bke shop etc...) this starts the process of rounding the taper on the cranks meaning the hole is now larger than the male counter part on the bottom bracket spindle which will now create play between the two. So, when you go to crank there will a little movement before the crank engages the spindle which will start to further wear out your cranks, so the problem will persist. You tend not to wear out your BB as it is steel where most cranks are made from softer Aluminium. There is no way to solve this other than buying new cranks. Regardless how tight you torque that bolt up it will still work loose as there is that bit of play, so overtightening is never going to help. You should never over tighten anyway there are reccomended torque levels as this is all that is required, if you needed to tighten a bolt until it was no longer coming out it would seem that there is a design flaw somewhere aling the line.With this in mind, I would suggest that you change your cranks, and whilst you are at, you might as well upgrade to ISIS drive, this eliminates the flat surfaces found on the square taper and the splined engagement will create a better pick-up, and your LH crank arm will not come loose.With any new bike you do need to periodically check the components, a new bike has never been ridden it has only been assembled by manufacturer and bike shop employee using a workstand, so during its first few rides it is very common that bolts will work there way loose and cabling will stretch and readjusting simply down to vibrtaion and cables bedding in. This is why bike shops offer an after sales service after approximetley 6 weeks times.Good luck on the crank shopping.REGARDSCALLUM Edited October 10, 2009 by 3001978 Quote Link to comment Share on other sites More sharing options...
tkD Posted October 8, 2009 Author Report Share Posted October 8, 2009 It has been mentioned, but to reiterate it sounds like you have started to round the taper on the crank (mostly happens with the left hand crank arm and on square taper cranks) Once you noticed that it was loose I presume there was a small amount of riding involved (i.e to get home / pub / bke shop etc...) this starts the process of rounding the taper on the cranks meaning the hole is now larger than the male counter part on the bottom bracket spindle which will now create play between the two. So, when you go to crank there will a little movement before the crank engages the spindle which will start to further wear out your cranks, so the problem will persist. You tend not to wear out your BB as it is steel where most cranks are made from softer Aluminium. There is no way to solve this other than buying new cranks. Regardless how tight you torque that bolt up it will still work loose as there is that bit of play, so overtightening is never going to help. You should never over tighten anyway there are reccomended torque levels as this is all that is required, if you needed to tighten a bolt until it was no longer coming out it would seem that there is a design flaw somewhere aling the line.With this in mind, I would suggest that you change your cranks, and whilst you are at, you might as well upgrade to ISIS drive, this eliminates the flat surfaces found on the square taper and the splined engagement will create a better pick-up, and your LH crank arm will not come loose.With any new bike you do need to periodically check the components, a new bike has never been rideen it has only been assembled by manufacturer and bike shop employee using a workstand, so during its first few items it is very common that bolts will work there way loose and cabling will stretch and readjusting simply down to vibrtaion and cables bedding in. This is why bike shops offer an after sales service after approximetley 6 weeks times.Good luck on the crank shopping.REGARDSCALLUMI don't have the money for new cranks, and the taper isn't round. Quote Link to comment Share on other sites More sharing options...
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