non drive side crank arm coming loose

[400bhp]

I have a feeling i need a new crank but thought i would ask the peeps here...

I was riding up a steep hill a week ago and the non drive side crank arm fell off

On closer inspection the safety pin had sheared in two
I put it back on, tightened it up and continued on my way

Got home and took it off and put it back om agaim

Anyway it has fallen off again today.

Its a hollowtech 2 fitting

Doing a short google search suggests the crank splines are probably worn due to the crank possibly being loose for a while. The crank is 18 months old and hasnt been removed from new

Any thoughts or experience?

 

[Dave Davenport]

Not sure what you mean by the 'safety pin'?

 

[Andrew_P]

I have a feeling i need a new crank but thought i would ask the peeps here...

I was riding up a steep hill a week ago and the non drive side crank arm fell off

On closer inspection the safety pin had sheared in two
I put it back on, tightened it up and continued on my way

Got home and took it off and put it back om agaim

Anyway it has fallen off again today.

Its a hollowtech 2 fitting

Doing a short google search suggests the crank splines are probably worn due to the crank possibly being loose for a while. The crank is 18 months old and hasnt been removed from new

Any thoughts or experience?

Similar happened with my 105 only mine chewed the splines as I stood up to pull away and was stuck at 6 o'clock (the same as the drive side) I had to ride home one legged.

I would definitely replace it, mine was my fault as I had changed the BB 3-4 months before, never could really figure out what the pin was going to do. It was working it self off on the ride and I did the same as you

 

[400bhp]

Similar happened with my 105 only mine chewed the splines as I stood up to pull away and was stuck at 6 o'clock (the same as the drive side) I had to ride home one legged.

I would definitely replace it, mine was my fault as I had changed the BB 3-4 months before, never could really figure out what the pin was going to do. It was working it self off on the ride and I did the same as you

Thanks. It's not chewed the splines, but I wonder if it's gone out of shape/worn the splines?

What about swapping the bb?

 

[400bhp]

Isn't the bb steel, so more likely to have worn the alloy crank than vv.

Yeah sorry I was talking balls. The BB has nothing to do with it.

 

[400bhp]

 

[400bhp]

Above is the offending crank. You can just about make out the indentations that have been caused by the crank shuffling about.

New crank ordered now.

 

[Andrew_P]

Thanks. It's not chewed the splines, but I wonder if it's gone out of shape/worn the splines?

What about swapping the bb?

I hadn't torqued the crank arm properly when I changed the BB I think mine chewed as it was on the edge of coming off, if you are changing the cranks you may as well do the BB, 105 Hollowtech II around £20

 

[fossyant]

View attachment 49201 View attachment 49203

I hope the missus didn't see you putting oily bike parts on the kitchen top !