Something that I've only met this year. It started during a ride about 20 miles from home but fortunately it was a centre bolt fitting and I had an allen key that fitted it. However within 10 miles I was having to stop and tighten it every couple of minutes. An LBS had an old crank of the same length which I bought to get me home.
I bought and fitted a new chainset which has been fine for several thousand miles until last weekend. After 42 miles the left had crank became loose and again did so many more times in the final 8 miles home. I fitted the previous replacement but in a test ride it was loose within 3 miles.
The original crank is on the left and the replacement on the right. The centre bolt incorporates a washer.
The next step is to replace the bottom bracket axle but are the cranks part of the problem?
It is likely riding the chainset loose has ruined the taper of the bottom bracket, which is now ruining any crank you put on it, by not being a proper press fit and allowing movement, enlarging the hole in the crank. You need to replace both the bracket and the chainset (check things are tight now and then too!).
1) having cleaned it scrupulously, so it is clean and bone dry, no grease 2) having added a little full strength threadlocking/bearing fitting compound to both sides of the taper. 3) using a hex head bolt, with greased threads, not the allen key one 4) using more (up to about half as much again) torque as is normally recommended.
The crank should be lubricated by the threadlock and the new torque setting will 'resize' the crank to some extent. Once the threadlock has gone off, provided the damage wasn't too bad then this may work well for ever. Immediately after fitting, check that the crank hasn't bottomed out in the taper; if it has, add a suitable washer (with a centre hole large enough for the BB spindle to go through) and retorque. Check the bolt torque after a hundred miles.
If you ever need to remove the crank, a little heat will degrade the threadlock enough to allow the crank to be removed.
If you don't have threadlock to hand, you can use epoxy resin instead.
BTW it is extremely unlikely that the BB spindle will have been damaged; it is hardened steel. Only the crank will have suffered permanent damage.
You may be wondering why this has happened in the first place. Some ideas;
a) bolt not tight enough b) grease on the taper (I know what shimano say... but it normally isn't a good idea!) c) bolt is too long and is bottoming inside the BB spindle before the crank is fully tight.
You can buy all new bits if the above repair doesn't work, but it is usually worth a go to try it....
The crank on the left in your photo looks like it has a rubbed surface on the inner face. I cant see why that should happen but if true it could indicate that it cant be tightened sufficiently as it is rubbing the left hand cup. Any chance of a pic of the crank in situ to counter this theory.
Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X2, Raleigh 20 stowaway X2, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840, Giant Bowery, Apollo transition.
I "cured" a loose crank by first heating it in boiling hot water before fitting. Obviously this expanded the hole in the crank and allowed it to go on a fraction further. It wasn't my idea but a cycling buddy suggested it. Never came loose again.
A man can't have everything.
- Where would he put it.?.
