Crank arm falling off

[Trickedem]

My 105 crank are keeps falling off
Before my latest ride I tightened it up and uses threadlock, but 5 mins into the ride it fell off
This is the third time this has happened. Any tips appreciated.
I was thinking of getting some longer bolts and putting some nylock nuts on.

 

[DCLane]

Where's the end bolt - the "crank fixing bolt"?

Also, there should be two allen key "crank arm pinch bolts" to tighten it on plus a small tab - a "crank retainer" - which stops it falling off. Are they there?

 

[Cycleops]

I can’t see the little tab washer that slips into the gap in the crank. Is it present.? Could be your problem.

 

[Trickedem]

The little tab was there. I bought some new ones, when it first happened. But I think they are fairly ineffectual as it is only a little pin. The bigger issue seems to be the bolts are not tight enough, maybe the thread on the arm is stripped

 

[Cycleops]

It’s possible the thread is stripped, could you feel it? I’ve never had that problem with my Hollowtech chainset.

 

[Trickedem]

I think so. I've got hollowtech on 3 other bikes and never had an issue.

 

[Gunk]

A complete 105 crank arm isn’t much money, I’d just replace it, sounds like the threads are stripped. I’ve never had one come loose.

 

[rogerzilla]

I don't think my only HT2 crank has the tab washer there, and never did. It's a secondary retention device which just stops the crank completely detaching if the two pinch bolts come loose, and should never really come into play.