Shimano crank arm fixing bolt size?

[zenitb]

Well okay then. It’s just that under normal fitting/use the plastic part shouldn’t be under so much pressure that it fails and if properly torqued those two bolts holding the crank arm on shouldn’t be coming loose:

Anyway, as I say I hope you get sorted.

yes, fair point to make keyboardmonkey - the role of plastic pre-load adjuster on Shimano's (patented) system is often misunderstood so it was worth confirming everone is on the same page - especially given it had got stripped somehow. My sons MTB mates just "tighten everything up" and then present me with the damage to fix, so this is the sort of scenario I have seen a few times. It was certainly worth checking the OP knew that its role is to adjust the lateral bearing float and that it should just take up the slack, nothing more.

Given the plastic bolt serves no structual purpose, if I was in the middle of an event I would probably eschew the (ok really nice) fine adjustment available on the plastic bolt. Not actually done this but could you not just shove the cranks together at an approximation of the end float, eliminate any obvious play, and then just bolt them up ? I suppose its possible you could get a bit of movement between the axle and the bearings (causing some axle wear) but I would have thought that would get you home at least..? Depends on the situation I guess...? Just asking the question so dont shoot the messenger !!!

[jamesofyorkshire]

That's what I did Zenith. I was about 15 miles from home when the crank became very 'wobbly'. I pushed the cranks together best I could and nipped up the torque bolts.

I'm guessing the torque bolts had come loose over time. Obviously the plastic cap thing wont hold a crank in place by itself during normal use.

This post was asking which plastic cap thing I should get as a replacement. That's all. No one has come up with an answer so I've ordered both....for a 5800 and a 7900. They have different thread lengths.