Left Crank Fell Off

[ianrauk]

Hollowtech II effectively has three retaining devices: the plastic tab, the preload nut and the two pinch bolts. For all three to fail would, IMHO, mean incorrect fitment.

Agreed. And it would take a pretty incompetent mechanic to muck it up.

 

[silva]

It's also possible that the 3 retaining devices are not parallel (ie as backing eachother up - 1 suffices in normal conditions) but serial "insurance", 1 failing = the entire mount failing. For ex, the 2 pinch bolts could prevent movement in direction X, the preload nut in direction Y, and the plastic tab for a centering. Or in other words: bad job on1 causing failure of other(s).
It must be for a reason, to have a mount with 3 components.

 

[figbat]

To remove the crank you have to:

1. undo and remove the pre-tensioning nut
2. Undo both pinch bolts
3. Lift the plastic locating tab.

Items 1 and 2 can be done independently but if doing only one the crank should stay in place, although doing (2) will make it loose. Item 3 is impossible to do unless item 2 has been done first - it is a backup to prevent the crank coming off. Even when you are trying to get the crank off and forget this tab it won’t come off until you remember it (BT,DT).

 

[hatler]

Early on a FNRttC ride we had a rider drop his left crank. I was TECing with I think Ross (or was it @ianrauk ) who immediately identified the problem as the plastic spacer. Counter intuitively (at least to me) a triple requires the spacer and a double doesn't. The rider had swapped from a triple to a double but had left the spacer in place.

ETA This was an HT2 crankset.

 

[fossyant]

Agreed. And it would take a pretty incompetent mechanic to muck it up.

The world is full of them though.

 

[Sittingduck]

Early on a FNRttC ride we had a rider drop his left crank. I was TECing with I think Ross (or was it @ianrauk ) who immediately identified the problem as the plastic spacer. Counter intuitively (at least to me) a triple requires the spacer and a double doesn't. The rider had swapped from a triple to a double but had left the spacer in place.

Lol what kind of moron would do such a thing?!

‘twas Friday 3rd Aug 2012, with a forced ride home due to Olympic train issues from Bri to Lon. Hard to believe that was almost 10 years ago!

 

[hatler]

Lol what kind of moron would do such a thing?!

‘twas Friday 3rd Aug 2012, with a forced ride home due to Olympic train issues from Bri to Lon. Hard to believe that was almost 10 years ago!

Bloomin' 'eck !! Impressed with your record keeping. I'd have put it, at most, at six years ago. That is quite scary.

The quick diagnosis resulted in possibly the fastest recovery from what I would have expected to be a terminal failure for a Friday's ride.

 

[Sittingduck]

Bloomin' 'eck !! Impressed with your record keeping. I'd have put it, at most, at six years ago. That is quite scary.

The quick diagnosis resulted in possibly the fastest recovery from what I would have expected to be a terminal failure for a Friday's ride.

Indeed, thanks to Ian and Ross and some creative use of a tyre lever to reload the HT 2 bearing we was back on the move and into Clapham Common asap. Credit to Strava and a bit of checking a particular rarely ridden segment to help identify the date. I was even just reminiscing by reading through the associated ride thread on here. How time flies

 

[Drago]

Incorrect fitment or not, themrider has some duty of care to ensure the machine is good to go, in much the same way that having an oil leak does not avpbsolve a new car own from blame if they fail to regularly check levels.

Regardless of what happened to the OPs lads bike, dilligent pre ride checks will identify issues such as this before damage is done.

 

[ianrauk]

Lol what kind of moron would do such a thing?!

‘twas Friday 3rd Aug 2012, with a forced ride home due to Olympic train issues from Bri to Lon. Hard to believe that was almost 10 years ago!

Wow... 10 years
I remember the incident clearly. Can't remember what bike of yours it was though.

 

[Sittingduck]

Wow... 10 years
I remember the incident clearly. Can't remember what bike of yours it was though.

Cube Streamer doing it's first Brighton trip!
Anyway - sorry OP we're not trying to de-rail this thread, just occurred that the problem sounded remarkably familiar. Hope you get to the bottom of it asap.

 

[Fredo76]

One of the flay rods has gone out-of-skew on the treadle.

 

[Ajax Bay]

One of the flay rods has gone out-of-skew on the treadle.

NM!

 

[Willam]

Same happened to mine, turned out to be worn spindles on the crank arm, probably caused by either incorrect fitting of the crank arm or fitting of the BB, the crank arm screws etc can not keep the arm in place if the spindles are shot, no matter if correctly tightened or fitted.

 

[itboffin]

Wow when I see left crank arm falling off I always think FSA because that’s their special feature but Shimano wow that’s new to me.