Deore Hollowtech 2 "Lock Ring"

Changing the cranks on my mates bike last night he sheared in two the plastic guide ring.

The arms are all nicely pinch bolted on and the bearings all run fine.

How important is this plastic ring? It's obviously not load bearing but does it do something other than keep the mud out?

It's just a preload thing for getting the cranks tightly on the axle isn't it? Bit like the top cap once you've done the stem up, I don't think it really does anything.

Might be wrong though.

doesn't even keep the mud out – it's only used for pre-loading the bearings before you tighten the crank arms. It does the same job as the top cap on a headset.

you can get them for £1.99 on wiggle/crc etc. Like grumm says it is just to preload the bearings until you tighten up the crank arms

Thats what I thought, I put plenty of pressure on while he pinched bolted the arms on and there's no play at all.

Good to ride?

Doesn't do anything once the bolts are done up. It's exactly like a headset top cap.

You can assemble them without it, but the sealing won't be as good without the preload, and it might develop play.

Probably best to get someone to pre-load it by hand while you tighten the bolts (or buy a new one for a couple of quid).

I would ride it.

By the way I don't think you really need to tighten that thing up very tight at all to not have any play in the cranks – maybe that's why it broke?

Yup, most of the tools that tighten them are designed so that you can only tighten them hand tight, as more than that and you could damage the bearings.

Just grab the crank arms (not the pedals) and give them a strong wiggle from side to side (ie in and out from the frame) and see if you can feel any play in the arms. If you can, then it would be best to re-tighten them, although there is a chance you may have overtightened them. Check that the cranks spin smoothly (without a chain on) – that way you can check if your BB bearings are ok.

I don't think there's any "maybe" about it!

There you go James… told you "it'll be fine" without it!

Cheers all.

Used my road bike for a couple of weeks without the cap. No problems.

I found I was over tightening with one of these anyway. I simply apply a bit of pressure to the crank arm with my knee & nip-up the pinch bolts, then torque correctly. Pop the cap in just to keep things clean / tidy.