Crank arm coming loose

[marting]

I replaced the chainset on my Single speed (Genesis Flyer) a few months ago (I'm now running a Miche Primato Advanced chainset).

Twice now the non-drive crank arm has come loose mid ride. Is there solution to this other than doing the bolt up RFT? The crank arm states to torque the bolt to 35nm, I'm dubious about going RFT as the old crank-arm was well and truly stuck (My crank arm extractor broke removing it).

Has my new crank arm killed itself when it first came loose, deforming the ally and now it'll never fit?

[Fluffsri]

Is this on a square taper? I had the same problem on my SS. In the end i ignored the torque value, applied lots of thread lock and grollied it in. Probably ridden a couple of hundred miles now and still tight, it was coming loose around 6/7 miles of riding.

[marting]

Fluffsri said:

Is this on a square taper? I had the same problem on my SS. In the end i ignored the torque value, applied lots of thread lock and grollied it in. Probably ridden a couple of hundred miles now and still tight, it was coming loose around 6/7 miles of riding.

Yep its a square taper. My SS only sees short journeys (my commute at ~5 mi/day), I reckon its come loose within 30 mi of last torquing it.

Its reassuring to know you've had the same issue and sorted it! I'll get some thread lock and swing on the wrench tonight

[Barchettaman]

Clean the inside thread of the BB with acetone on a Q-tip, the crank arm bolt with acetone on a bit of rag, to remove any old threadlock. Allow to dry.

Apply threadlock (Loctite Blue should be fine) to the crank arm bolt.

Go gorilla on the bolt, should be fine.

[walm]

Whatever you do, try not to ride on a loose arm.
Those Miche Primatos aren't cheap and I had to just dump a set after I deformed the hole the square taper fits into.

[AyBee]

Barchettaman said:

Clean the inside thread of the BB with acetone on a Q-tip, the crank arm bolt with acetone on a bit of rag, to remove any old threadlock. Allow to dry.

Apply threadlock (Loctite Blue should be fine) to the crank arm bolt.

Go gorilla on the bolt, should be fine.

This. I've had the same issues with my singlespeed numerous times and locktite blue usually makes sure it doesn't come undone!

[thiscocks]

Shouldnt need to use threadlock on them. If its coming loose with 30nm on it then the arm is deformed.

[ecsrobin]

I thought square taper was long since dead?? If it's coming off after that short a distance I would say the crank arm is deformed.

[walm]

ecsrobin said:

I thought square taper was long since dead?? If it's coming off after that short a distance I would say the crank arm is deformed.

For some reason they are all the rage on fixies/SS - I have had three of them. [/hipster]

[Fluffsri]

walm said:

ecsrobin said:

I thought square taper was long since dead?? If it's coming off after that short a distance I would say the crank arm is deformed.

For some reason they are all the rage on fixies/SS - I have had three of them. [/hipster]

Mines an old Middleburn, quality kit and years old lol

Edited by Fluffsri on Friday 2nd October 12:36

[AyBee]

ecsrobin said:

I thought square taper was long since dead?? If it's coming off after that short a distance I would say the crank arm is deformed.

I had a spate of crank arms coming loose until I used locktite on the bolt thread, which would suggest otherwise...

[TwistingMyMelon]

I wouldn't overthink it, bit of threadlok and torque it a bit higher than the recommended level.

[walm]

It's completely binary. Either your crank arm is bent and it will work itself off threadlock or not - or your crank arm is fine and threadlock+torque will solve the whole thing.

My f@cked crank arm was very obviously f@cked. You could see the deformation in the corner of the square bit.

[ecsrobin]

walm said:

ecsrobin said:

I thought square taper was long since dead?? If it's coming off after that short a distance I would say the crank arm is deformed.

For some reason they are all the rage on fixies/SS - I have had three of them. [/hipster]

I'm guessing it's because they're are so cheap?

[walm]

ecsrobin said:

walm said:

ecsrobin said:

I thought square taper was long since dead?? If it's coming off after that short a distance I would say the crank arm is deformed.

For some reason they are all the rage on fixies/SS - I have had three of them. [/hipster]

I'm guessing it's because they're are so cheap?

I dunno - the UN55 and UN26 are £10-15 usually, while the hollowtechs, octalinks and powersplines are all in the £10-20 range too.
Not sure there's a huge price difference.
Campag square taper is £50!

[wobert]

If using Loctite, make sure the bolt and threaded hole are oil and grease free.

Any hint of oil / grease will make the Loctite less effective in holding the bolt in place.

Also leave to "cure" for 24 hrs to make sure the Loctite goes off properly.

[deadtom]

marting said:

I'm dubious about going RFT

Fluffsri said:

i ignored the torque value ... and grollied it in.

marting said:

I'll ... swing on the wrench tonight

Barchettaman said:

Go gorilla on the bolt

I am enjoying all the euphemisms for mechanical belligerence. keep 'em coming.

[marting]

walm said:

I dunno - the UN55 and UN26 are £10-15 usually, while the hollowtechs, octalinks and powersplines are all in the £10-20 range too.
Not sure there's a huge price difference.
Campag square taper is £50!

Or Phil Wood square tapers at £75!

[Dammit]

You've got nothing to lose by over-torquing it, the head of the bolt might shear off I guess but it sounds very much like the crankset is dead anyway so you may as well go for it.

When you decide you've had enough get an old 165mm Shimano crank and the USE converter ring:



And rock out with your cock out.

[AyBee]

AyBee said:

Barchettaman said:

Clean the inside thread of the BB with acetone on a Q-tip, the crank arm bolt with acetone on a bit of rag, to remove any old threadlock. Allow to dry.

Apply threadlock (Loctite Blue should be fine) to the crank arm bolt.

Go gorilla on the bolt, should be fine.

This. I've had the same issues with my singlespeed numerous times and locktite blue usually makes sure it doesn't come undone!

Well it would look like I royally jinxed myself with this response. Less than a week later and I've properly rounded the square taper to the extent that no matter how tight the crank bolt is, the left crank is all over the shop I'm tempted to take this opportunity to upgrade to external BB and am wondering what my options are. Has anyone used a BLB Notorious crank or am I better off with a Sram Omnium? I have a Goldtec rear hub so suspect it's got a chainline of 46mm which would leave me with a 4mm difference in chainline front to back with either of those options