Originally Posted by
am8117
I have seen the fixing bolt (I believe that's Shimano's own designation for the plastic cap on 2-piece cranksets) with all the threads stripped off, right crankarms with splines imprinted into their smooth part (as it was sliding off while the plastic was being pulled out gradually) and the stopper plate having it's pinned ripped off in the process of doing so.
Now there are enough videos on YouTube suggesting that the stopper plate pin is a safety feature to prevent such occuring but it is non-sense even without having seen the above-described having happened. It is safety in the sense it helps to fix the parts in place in correct configuration, but it's the pinch bolts holding all the load just like with the stem and steerer case.
So no the plastic parts are not load bearing and if they become they fail. But I do not know why Shimano does not seem to be putting any thread locker on the pinch bolts on the cranks I have seen. They have a dab of their Shrek gooey thing on the O-rings on the spindle and they have some white greasy substance all clunking up the stopper plate area, but no thread locker on the bolts.
The more I was surprised why they doubled the length of the fixing bolt (plastic screw) on new cranks.
It's only certain types of installations that need thread locker. Most bolts will stay perfectly tightened to their prescribed torque with no thread locker on them.
Don't try to twist what I said about the stopper pin preventing the crank from coming off. The crank arm bolts are what does that. The pin would only serve to plow that grove in the spindle. Absence of a grove plowed in the spindle and the crank arm falling off to me would indicate the bolts weren't tightened sufficiently or the stopper plate was never able to be properly engaged.