Worn out Dura-Ace crank

[Johan Bornman]

Just wondering' date=' can a Dura Ace crank 'spindle' wear out (external BB)? Here's the scenario, crank used for a long time (years!) but eventually it is not possible to tighten the non drive side enough. It keeps coming loose!

 

The non-drive side crank has been replaced but it makes no difference, thus leading me believe that it is something to do with the actual 'spindle' thingy on the shaft ........

[/quote']

 

Ben, I'd love to help but I have difficulty understanding the symptomes and the components causing the problem. I'm a bit slow lately.

 

Is it a modern crank where the right crank is permanently attached to the spindle and the left crank fits on a splined end with a pinch bolt design?

 

I cannot imagine a scenario where the pinch bolt will no longer tighten but please help me understand the problem.

 

 

[Racer X]

BB - It happened to an LX hollowtech two I had. I sat there and re-cut the threads which sorted the prob out.

[NotSoBigBen]

JB - yes it is as you describe a 'modern' crank.

[greatwhite]

 

Is it a modern crank where the right crank is permanently attached to the spindle and the left crank fits on a splined end with a pinch bolt design?

A series 7800 crank set - the soon to be replaced current one on the market

 

 

 

I cannot imagine a scenario where the pinch bolt will no longer tighten but please help me understand the problem.

 

In a nut shell, if the splines wear down the circumference is reduced, meaning effectively the pitch of the splines is reduced. If you are even 1/4 pitch out across the entire circumfence, the 'teeth' on the inside of the crank arm, whos pitching remains basicly unchanged, won't engage properly with all the splines. - Net result, tightening the nut almost to the point of striping will still not fix the problem of the arm engaging the shaft cleanly

 

[greatwhite]

 

BB - It happened to an LX hollowtech two I had. I sat there and re-cut the threads which sorted the prob out.

 

Threads of splines?

 

[NotSoBigBen]

BB - It happened to an LX hollowtech two I had. I sat there and re-cut the threads which sorted the prob out.

Threads of splines?

 

Wondered the same? The left arm is new so it has new bolts as well!

[Johan Bornman]

OK, I get it.

 

If the splines (those ridges on the spindle and inside the crank), are damaged, your crank is toast. I can't see why the splines on the spindle would suffer since the softest part is the crank and those splines will be damaged before the steel ones.

 

Inspect the inside of the hole for spline damage. If the splines stil have enough body, look at the second culprit, which would have something to do with the pinch bolts. These could either be stripped (again, in the crank rather than the steel bolts) or, something is making the pinch opening bottom out. If the threads in the crank are stripped, it could be an easy repair with a cheap thread insert.

 

I don't agree with Great White's analysis that the splines' pitch would change. The pitch is the distance from spline to spline. Lowering the ridges as would happen by wear, would keep the pitch intact, although the splines would become shallower. Just a little technical point.

 

 

[NotSoBigBen]

Thanks JB - tonight I check it with a fine tooth comb! Just to clarify though these are not cranks that I have used, they were given to me as the owner had given up on them so I am trying to see if I could use them myself.

[Ox_Wagon]

JB is correct the pitch should not change but the outside diameter and/or width of the spline spline could reduce causing the splines not to engage properly with the crank arm.  It sounds like someone used it while it wasn't properly tighten. <?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

It sounds like the classic BB problem. You got the same effect with square taper cranks that the BB and crank gets so badly damages that there is play irrespective of how tight you crank the bolt.  That is one of the reasons Shimano started <?: prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Octalink (ISIS etc) which is ironic in this case.

 

There is always epoxy if you know your not going to remove the crank any time soon.

 

If you through the crank in the car, I can have a look at it...... Can't promise anything.

Ox_Wagon2008-07-01 01:40:14

[greatwhite]

I don't agree with Great White's analysis that the splines' pitch would change. The pitch is the distance from spline to spline. Lowering the ridges as would happen by wear' date=' would keep the pitch intact, although the splines would become shallower. Just a little technical point.

 

[/quote']

 

I wondered how long it would take someone to tell me I'm wrong. I did say 'effectively' the pitch has changed, because the useful part of the spline is the top, not the root - when I did the original post I though it might be a worthwile excercise to do a few simple 'sketches' in CAD to demonstrate, but was busy 'paying the bills'. If I get a chance I'll do them and post.