Crank slipping advice

[scout05]

Good evening,

Just looking for advice to save myself some money

I have been having issues with my no-drive crank slipping, a few months ago I have my bike serviced and since have had issues with the crank, firstly the retaining bolt came lose and fell out, after replacing this a few weeks later the crank slipped which I just sorted on the road side.

A few weeks after this it slipped again and now I can get it to hold at all.

I can't remember what was done during the service but there was something to do with the bottom bracket, I'm not looking to blame just find the issue. Should the thread be flush with the crank (see picture)
I suspect it is just the grooves have worn on the crank as they are only prominent as you can see in the picture and nothing to interlock with on the bottom bracket and in the tight screws have just been holding it in the place the last few months?


I can't find a picture to see what the crank should look like

 

[Cycleops]

I think that is a Hollowtech. Looks like the crank is not pushed on far enough and there should be a plastic screw pre tensioner (1) which is done up using hand tight with the Hollowtech plastic tool wheel. I presume you have tightened the two pinch bolts? And the small plastic spacer underneath is present.
If the splines are damaged it probably means a new crankset.



Hello and to CC

 

[scout05]

Yes, I had to order a new plastic bolt.
I will have to check if the spacer there, thanks

 

[wafter]

Are both the clamping bolts present in the crank arm; you're not just trying to run the arm fitted with the plastic preload "plug" are you?

If the clamp bolts are present and tight the splines in the arm must be absolutely ruined to be slipping on the axle.. can't see how that could be the case tbh.

 

[Dogtrousers]

If the clamp bolts are present and tight the splines in the arm must be absolutely ruined to be slipping on the axle.. can't see how that could be the case tbh.

I too am a bit baffled by how a hollowtech crank could slip unless the bolt wasn't done up much at all or was absent.

But I'm easily baffled. The wrong end of the stick is my favourite end.

 

[ColinJ]

... there should be a plastic screw pre tensioner (1) which is done up using hand tight with the Hollowtech plastic tool wheel.

That is likely to be too tight!

I have just converted one of my bikes to Hollowtech so I double checked how to do this. Apparently it should be done up only just enough to take up the slack, no more, so lightly finger tight! (If too tight, lateral pressure on the BB bearings will cause friction and premature wear.)

The hook on the 'spacer' clips into a hole on the BB axle. Some people suggested that it is a safety feature to stop the crank falling off if the 2 crank bolts come loose. It would also reduce the chances of someone cracking the end of the crank by over tightening the bolts.

Tighten those 2 bolts alternately a bit at a time. Do NOT tighten one up fully, then the other! Ideally, use a torque wrench to end up with both bolts torqued to 12-14 Nm. If you are going to guess then that it is like hanging a 4.5 kg (10 pound) weight off a 30 cm (12 inch) long allen key. Tight, but not gorilla-tight!

PS In case it isn't obvious... Do the gentle preloading with the plastic bolt with the 2 crank bolts loose, leave it in place, and then tighten the bolts as described above. The split end of the crank should tighten up slightly on the plastic bolt and stop it falling off later when riding.

 

[scout05]

Are both the clamping bolts present in the crank arm; you're not just trying to run the arm fitted with the plastic preload "plug" are you?

If the clamp bolts are present and tight the splines in the arm must be absolutely ruined to be slipping on the axle.. can't see how that could be the case tbh.

Yeah everything is there, this is what I'm trying to figure has changed as don't believe I will have worn them down that much it doesn't even just sit place.
Think I need to try have a look at 'working' one to compare, can't quite see from pictures online

 

[the snail]

I would pull the crank off the spindle and check the condition of the splines. I would expect the crank to be further onto the spindle - I wonder if the BB was replaced? If you can find the model number of the crankset and BB (embossed on there somewhere) then you could check if the parts are correct for each other and you have the correct spacers fitted.

 

[scout05]

That what I am thinking, had another look this morning and the 'teeth' are completely worn but only at the edge, so thinking it has just been holding on but completely gone now, so if it could be pushed on more it looks like it would be fine but there is no space to push it on more. Will check the compatibility tonight

 

[Chislenko]

I have oft heard about these spacers.

I have two bikes with Hollowtech and neither has a spacer fitted.

I have never encountered any problems.

Doesn't help the op mind, just curious why mine don't have the spacers!

 

[chriswoody]

but there is no space to push it on more

You mention there was work on the bottom bracket, along with the statement above I'm wondering if the correct spacers are fitted on the Bottom Bracket. If there are too many or in the wrong place then the crank spindle will not protrude enough through the Bottom Bracket.

The Image should help a little in determining the spacers needed.

 

[wafter]

How much engagement is there between the

You mention there was work on the bottom bracket, along with the statement above I'm wondering if the correct spacers are fitted on the Bottom Bracket. If there are too many or in the wrong place then the crank spindle will not protrude enough through the Bottom Bracket.

View attachment 732871
The Image should help a little in determining the spacers needed.

Indeed - possible that the wrong (excessively wide) BB / excessive spacers have been fitted, reducing engagement area and causing damage to the splines when torque is applied over this reduced contact area..

 

[Cycleops]

I would pull the crank off the spindle and check the condition of the splines. I would expect the crank to be further onto the spindle - I wonder if the BB was replaced? If you can find the model number of the crankset and BB (embossed on there somewhere) then you could check if the parts are correct for each other and you have the correct spacers fitted.

No need to check the model all bearings for Hollowtech sets are the same.
On my 68mm she'll there two spacers on the right and one on the left.

 

[ColinJ]

No need to check the model all bearings for Hollowtech sets are the same.
On my 68mm she'll there two spacers on the right and one on the left.

Whereas on my 68 mm... there are no spacers!

Obviously, spacers would have been needed if the crankset had been designed for a 73 mm BB shell.

 

[Chislenko]

Whereas on my 68 mm... there are no spacers!

Obviously, spacers would have been needed if the crankset had been designed for a 73 mm BB shell.

Right, I am not the only one without spacers. That makes me feel a lot better.