Crank bolts coming loose

[TheLegend]

The crank bolts on my shimano octalink bolts keep coming loose.

Didn't have a prob for lets say 6 months after installing them, then first the left side gave me troubles, which I sorted by putting a different crank arm on, and now, just 2 rides after that my right side keeps coming loose! Last 70 k ride I had to tighten the bolt 3(!!) times (luckily I had Flemish Lion&wife's b'day present with me and could rescue myself ).

Has anyone got a tip what the cause could be? any other "ouma"-tricks apart from locktite (I am already in the process of applying it - my hands still smell from the spiritus i used to degrease)?

 

thx

 

[GoLefty!!]

loctite 242

[shaunh]

Put some Loctite threadlock on the bolts before inserting & tightening them. This should solve your problem!

[TheLegend]

yes yes, thanx - as I said I am in the process already.

But what's the damned cause? They shouldn't come loose!

 

[shaunh]

Use a Torque Wrench and torque to the corrent settings.

[Johan Bornman]

Octalink was one of Shimano's biggest follies and a miserable failure. Shimano didn't abandon it without good reason.

 

I've written about this in detail before, if you search for Goofy or Hotfoot and Octolink you'll come across the problem.

 

Your solution isn't some sort of glue like loctite but a new crank. It is probably ruined.

 

This design suffered from lash. 90% of the population don't have a problem with Octalink because they descend in the hotfoot position with their right lef forward. However, the goofy descenders put reverse lash on the link and the bolt "cracks" loose over a bump. The soft alumunium splines quickly wear when the bolt is loose and it is ruined within one ride.

 

 

 

 

[TheLegend]

thanx.

 

what a ***!

 

[GoLefty!!]

Hmm I seem to have missed this octalink probelm cos I had a Cannondale CX2 chainset that fit on a  Dura Ace BB (which is not actually Octalink).

 

Still I always used loctite on thos bolts and they never came undone

[Johan Bornman]

Hmm I seem to have missed this octalink probelm cos I had a Cannondale CX2 chainset that fit on a  Dura Ace BB (which is not actually Octalink).

 

Still I always used loctite on thos bolts and they never came undone

 

Tim, I think loctite is a good solution to prevent the bolts from falling out. However, the lash is so powerful that it will still loosen the bolt, even if it won't fall out.

 

The spines are too poofter for this powerful application and if the bolt is loose just in the slightest, it will lash.

 

I assumed you wanted to put Loctite on the splines.

 

 

Interestingly enough, Octalink was a disaster on three fronts - the splines as I mentioned, the fact that the spline engagement was blind, so one could easily make a mistake and ruin them and thirdly, in the roller bearings on the axle. Those quickly self-destructed because Shimano forgot that rollers don't work well with grease and prefer oil.

 

Shimano employs more engineers than any other profession in the company - they say, but on the day that the Octalink was conceived, all the engineers were designing fishing reels.

 

It is still a good company that makes superb products 

[Ox_Wagon]

Hmm I seem to have missed this octalink probelm cos I had a Cannondale CX2 chainset that fit on a  Dura Ace BB (which is not actually Octalink).

 

Still I always used loctite on thos bolts and they never came undone

 

Shimano employs more engineers than any other profession in the company - they say' date=' but on the day that the Octalink was conceived, all the engineers were designing fishing reels.

[/quote']

 

 It is a good one that I need to remember!

Ox_Wagon2008-10-20 08:38:56

[GoLefty!!]

Hmm I seem to have missed this octalink probelm cos I had a Cannondale CX2 chainset that fit on a  Dura Ace BB (which is not actually Octalink).

 

Still I always used loctite on thos bolts and they never came undone

 

Tim' date=' I think loctite is a good solution to prevent the bolts from falling out. However, the lash is so powerful that it will still loosen the bolt, even if it won't fall out.

 

The spines are too poofter for this powerful application and if the bolt is loose just in the slightest, it will lash.

 

I assumed you wanted to put Loctite on the splines.

 

 

Interestingly enough, Octalink was a disaster on three fronts - the splines as I mentioned, the fact that the spline engagement was blind, so one could easily make a mistake and ruin them and thirdly, in the roller bearings on the axle. Those quickly self-destructed because Shimano forgot that rollers don't work well with grease and prefer oil.

 

Shimano employs more engineers than any other profession in the company - they say, but on the day that the Octalink was conceived, all the engineers were designing fishing reels.

 

It is still a good company that makes superb products 

[/quote']

 

 

Loctite on the spline, good heavens never

 

I agree octalink was spawned by the devil himself. It still somehow managed to be better than I.S.I.S. even though that system had a better spline interface.

 

A switch to HollowTech II would be the ultimate solution but also far more expensive.

 

The lash in the splines was unfortunate and I've seen XT level cranks destroyed in 50km. The only answer  then is to fit it too a Dura ace BB which had fewer but wider splines and basically broach new splines into the crank arms.

 

Somehow the CX2 Chainset was immune to lash but it was a solid piece of kit and rather weighty.

[TheLegend]

 

why on earth are the one piece crank sets with bearing so much more expensive than the mtb ones? bloody....

 

 

oh ja, I put loctite on the bolt now and will try it out tomorrow. it better holds or I'll be pissed! and wet, cause it's supposed to rain!

TheLegend2008-10-20 14:48:11

[GoLefty!!]

did you clean the htreads before putting the loctite in there?

[TheLegend]

of course!

my fingers still smell like spiritus and only walking down into the basement makes you dizzy from the fumes

 

[Slave]

I had / have the same problem with my old Peugeot and have seen the problem on a number of other bikesas well.

 

No matter how much toque I used to tighten the bolts, they would just keep on working loose. Other solutions I tried were new crank and bolts (nuts on my bike).

 

Loctite was the only solution (no pun intended) that worked for me.

 

Personally, I think that the bike manufacturers build this fault into the bike so we are forced to buy more spares and contribute to their bottom line. If this is not true, why don't they go back to older systems that actually worked. In the old days, cottar pins did the job and very seldom came loose or gave any problems.

[Johan Bornman]

I had / have the same problem with my old Peugeot and have seen the problem on a number of other bikesas well.

 

No matter how much toque I used to tighten the bolts' date=' they would just keep on working loose. Other solutions I tried were new crank and bolts (nuts on my bike).

 

Loctite was the only solution (no pun intended) that worked for me.

 

Personally, I think that the bike manufacturers build this fault into the bike so we are forced to buy more spares and contribute to their bottom line. If this is not true, why don't they go back to older systems that actually worked. In the old days, cottar pins did the job and very seldom came loose or gave any problems.

[/quote']

 

All is not what it seems. I assume your old Peugeot had a square taper crank and the Octalink problem doesn't apply here.

 

Square tapers have a life of their own that few people understand. The taper is 2 degrees and the aluminium crank is pressed onto the steel taper by torquing (SP?)  it with the crank bolt.

 

If the tapers are not greased before torquing, the torque wrench reading is meaningless and the actual press fit is random.

 

As you pedal, the leading edge surfaces on the taper are compressed and the trailing edge edges relieved of some compression.

 

This causes the aluminium crank to squirm on the steel axle. The squirm releases some stress residual from the fitting of the crank and it settles in a new position. Since there is a crank bolt there that prevents it from coming off, it walks upwards - in other words tighten itself. The bolt then is loose and if the bolt retention cap (it isn't a dust cap since we're not interested in preventing dust from going in there but in preventing from the bolt falling out) isn't on, you lose your bolt.

 

The crank is then on so tight that the bolt is not needed and you can safely ride the bike without a bolt.

 

However, if the bolt fell off because the whole assembly wasn't torqued enough, the crank will work loose and ruin itself within a single ride.

 

There are some weaknesses in a square taper crank but they far outweigh its benefits. One of them is a weak axle. Due to the small diameter of the axle, even a solid axle is not strong enough for some beasts and they regularly break it. Another weakness - and you all know where I stand on this one - is weight. It cannot be made lighter without increasing the diameter of the axle. That allows for a reduction in material by making it hollow and a reduction in weight.

 

Ruined cranks from bolts working loose are enitirely the mechanic's fault and not a weakness in the design.

 

Cotter cranks on the other hand are rubbish. The cotter/axle interface is too small to withstand the rigours of athletic or even sedentary pedalling and these quickly fail. Further, there is no elegant way of removing them other than using a sledge hammer. The world is a better place without cottered cranks.

 

For those of you born after the goold old days, this is a cotter crank. Wave it goodbye.

 

http://www.bike-classique.com/cotter.jpg