[Help] Crank arm falling off

[Amberdrake]

Those 2 screws are bit of a pain. The Required torque setting is high enough that if HEX key doesn't fit 100% you will strip them. (Been there done that).

[Reme Le Hane]

I have not touched those since I got the bike last year, but it was 2nd hand, it's been in for a full service once since then.

 

It popped off just before the event start, could of been worse, I had just touched it when it fell off so, rather than than on the drive over. Was about 40km before it fell off again, but looks to start slipping around 15-20km.

 

Will see what the bike shop says when I take it in later, hopefully it's not a new crank.

 

Thanks guys.

[Alouette3]

I am pretty sure you won't have the tool to tighten the cap screw so probably best to get your LBS to do the whole job for you. 

Next problem for you will be, Does cool heat have stock of that item?

Like mentioned before that screw doesn't tighten the crank to the shaft, So you actually don't make it very tight as you could damage the BB but it all helps with keeping the crank on. In theory the crank shouldn't come off if those other 2 screws are tight enough.

If you don't have the tool. the end of some Shimano quick release levers work a treat!

[Fast-er]

So i had the same problem about 2 months ago. 

 

Was commuting the one morning and all of the sudden my crank-arm came off. Found that my BB came loose and caused the crank-arm to come off. so...

 

1. Check your BB. 

2. That plastic cap is there for a reason. I payed R10 for a new one. 

3. Make sire that weird lock-type thing on top of the 2 bolts is secured properly.

 

Never had a issue with my crank again 

[Martin PJ]

Its not supposed to be tightened with an Allen Key... its only there for preload tension!

Good point, I don't tighten it very tight. Just enough to get the crank on the shaft nicely. With the original Shimano cap they have deliberately come up with design that will prevent you from tightening up this cap too tight, it isn't a load bearing part.

 

On my crank the shaft splines are very slightly damaged, I think this is why it is not holding.

[Reme Le Hane]

So back home now, took a look at the bike, thread looks fine no obvious damage there, but what I did see is there there is no pin on the locking clip itself, so i you look @ https://www.amazon.com/Shimano-Hollowtech-Crank-Arm-Safety/dp/B003RLNCS6, the metal piece sticking out is not there.

Personally it does not look to give too much support, but with everything else looking good, that seems to be the most important piece that NOT there.

[dev null]

That pin has got nothing to do with your problem. As other mentioned, without the black cap you would not have had preload tension on the BB, and the crank probably wiggled from side to side as you pedalled, gradually working itself off the spline.

 

Most important thing is to look for damage on the splines, both on the shaft and the crank itself. I suspect that there will be some flattened splines. In that case, new crankset.

 

Put this down to some school fees to learn and do some basic maintenance on your own bike. It is not hard and there are tons of videos available.

[Reme Le Hane]

That pin has got nothing to do with your problem. As other mentioned, without the black cap you would not have had preload tension on the BB, and the crank probably wiggled from side to side as you pedalled, gradually working itself off the spline.

 

Most important thing is to look for damage on the splines, both on the shaft and the crank itself. I suspect that there will be some flattened splines. In that case, new crankset.

 

Put this down to some school fees to learn and do some basic maintenance on your own bike. It is not hard and there are tons of videos available.

 

As I said, I checked the splines and not are flattened, and as for the little pin, its whole purpose for existing is as a last step to keep the crank arm from walking itself off, so yes the tension needs to be properly reapplied, but locking clip also needs to be replaced, and I have already confirmed all of this with my LBS who is ordering in the parts before I take it in tomorrow.

 

Not going to help only fixing half the problem.

[dev null]

As I said, I checked the splines and not are flattened, and as for the little pin, its whole purpose for existing is as a last step to keep the crank arm from walking itself off, so yes the tension needs to be properly reapplied, but locking clip also needs to be replaced, and I have already confirmed all of this with my LBS who is ordering in the parts before I take it in tomorrow.

 

Not going to help only fixing half the problem.

 

O, OK. By mentioning threads, you actually referred to the splines. By all means get a new clip, but black cap most importantly.

[Reme Le Hane]

O, OK. By mentioning threads, you actually referred to the splines. By all means get a new clip, but black cap most importantly.

Ya that they have there for me already, thankfully, being the more important part, good thing I wasn't riding early this week, oak Valley was not as ready for it as I had thought.

 

Sent from my 2014817 using Tapatalk

[Eddy Gordo]

I had the same problem with my road bike Ultegra crank. It turned out that I had some damaged splines and was quoted on getting a new one.

Instead I bought a small enough metal file, file the splines straight and fitted the lock hook thing(after 1000km no issues at all). This hook is supposed to fit in a small indentation on the BB so that the arm does not work its way off the BB.

 

Just make sure its all fitted and torqued proper.