[Closed] Crank cap.....what does it do??

No, its to preload the bearings. The pinch bolts hold the cranks on (assuming your on about shimano)

If you are talking about an external bottom bracket type set up then the cap just preloads the bearings and holds the arm in place while you do up the bolts. If you over tighten it you can actually decrease the life span of your bottom bracket bearings.

As david says. Assuming you mean HT2, earlier models its just a dust cap. Its the same system as the top cap on the stem

Yes, slx.

"preload the bearings"??

I've fitted new bb and put on cranks using pinch bolt, I just dont understand what the crank cap does and concerned that i might be over/under tightening.

Sorry!!

[pedant]you shouldn't be putting any preload on the bearings - its to remove endfloat [/pedant}

have you read the instructions?

imagine it's like a cup and cone bearing hub - you need to tighten the nuts enough to stop the wheel rattling on the axle but not so much that it binds.

For Shimano HT2 'finger tight with the proper tool' is normally about right.

park tool site is worth a look.

http://www.cyclistno1.co.uk/features/maintenance/shimano-ultegra-hollowtech-ii-crank-service.htm

The cap basically takes up the slack so the axle/cranks don't slop around (in laymans terms) 🙂

Thanks, its becoming clearer now. There weren't any instructions but it was pretty self explanatory (apart from the crank cap which just looked like a 'spare part' that could easily be thrown away!)

Finger tight it is

Have you got the crank cap tool?

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If not you can use some fine nose pliers splayed out?

And you tighten this cap BEFORE you do the crank bolts up.

If not you can use some fine nose pliers splayed out?

And you tighten this cap BEFORE you do the crank bolts up.

Sorry but thats wrong. The pinch bolts hold it on, not the end cap!

But the pinch bolts don't "pinch" without the cap. Trust me 😳

Oh bloomin eck - the end cap pulls the non-drive cranks onto the axle splines and then the pinch bolts then tighten the crank arm onto the spines!

If you think you need the cap to hold the arm on that would suit the user name wrecker...it does the same job as a stem top cap.

Nah, if you don't have the cap on, NDS arm falls off. Technically, this shouldn't be the case but in practice is definitely is.

you tighten up the top cap to remove any play, you then tighten the pinch bolts.

What you will find is that the pinch bolts tighten up and clamp the cap in place. Means the crank is going nowhere.

IF you don't believe me try and remove the top cap before and after doing the pinch bolts up.

echnically, this shouldn't be the case but in practice is definitely is.

fortunateson09: Have you lost the odd shaped (like a "9") washer that's in the pinch bolt? It has a pin that locks into a hole on the cranks splined shaft. Another and probably the most likely cause of your NDS crank arm dropping off. I'm struggling to believe that the end cap is engineered to (i.e. was) holding you crankset on......like all things I could be (ok, probably am!) wrong!

The instances I have seen where the crank cap comes off then the arm comes off are nothing to do with the top cap holding the arm on. What happens is the splines in the arm are damaged, usually through being ridden with the pinch bolts not tight enough or one done up then the other which can deform the arm. Then the arm works outwards, pushes the end cap off quite easily and falls off. A small piece of plastic really doesn't hold the arm on.

I did away with the plasic spacer with the little metal pin that stops the crank falling off, as I kept forgetting to hook it up when trying to take the crank arm off. 😳

[pedant]you shouldn't be putting any preload on the bearings - its to remove endfloat [/pedant}

That's not being pedantic. Being pedantic would be adding an excessive and academic level of accuracy just for the sake of it. Your comment is absolutely 100% necessary and relevant.

lost mine months ago and the crank hasn't come off.
I'm really asking for it now...