I have a Miche chainset on my commuter. It has a splined bottom bracket and the offside crank (non-driveside) keeps loosening.
I’ve tightened it up and it happens again, put threadlock on it, same again, pulled it apart, checked for wear (looks ok) and re-greased it and it’s happened again – every 50-60 miles of use.
It’s only 6 months old so it’s not worn.
Any idea what the problem is and how to fix it?

@brooess

unfortunately its time for a new crank arm

your existing crank arm has a “flogged out” crank axle socket (the boss which fits over the BB axle) and it will just continue to work loose under load

there are various things you can try (as you have tried), but there is no real fix except for a new crank arm

How’ve I managed that? It’s only been ridden on the commute, twice a week for 6 months!
That’s surely a warranty replacement?

the Miche cranks always seemed a little soft (like many of the smaller brands) when I worked at Evans, its something I have seen before. The worst were FSA whose alloy cranks seemed to be made from cheese!

warranty can be tried, but they may claim its “bad fitment” or “lack of maintenance” rather than admitting they use cheap (soft) aluminium alloy

Thanks. I got the bike, fully built from RJ Chicken so I’ll go back to them direct…

I’ve had 2 slx cranks fail in this way on the same bike – would love to know why

@tops 5

I would check the BB spacing of your bike. Its not uncommon to find Shimano HT2 cranks with incorrect BB spacing (too many spacers between BB cups and BB shell on frames with 73mm)

on 73mm it should be 1 x 2.5mm spacer on driveside, on 68mm its 2 x 2.5mm on driveside and 1 x 2.5mm on non driveside

this can cause a lack of engagement between the non-driveside crank arm and the axle stub

this will quickly strip out the splines, however its normally caught during assembly as the plastic safety plate with the steel pin will not engage into its pin locking hole on the axle if this spacing is incorrect.

other thing to check is torque on the 2 pinch bolts, both should be around 13nm with torque wrench to balance the clamping force shared across the non-driveside arm socket

Thanks for the info esher – it’s 1×9 with just a bb mounted stinger and no other spacers tho