Crank Torque Conundrum

Dear cyclist folk.

I've just put a crank arm on a bike . . . . . . (the recommended torque is 38-42Nm)

Stupidly I was looking at the wrong gauge on my torque wrench, so instead of putting it on at 40Nm I put it on at 40ft-lb.

This means I actually put it on at around 55Nm, which is damn tight !

In fact it's so tight that the hex bit broke as it hit 55Nm!!!

So, my question, firstly I am going to leave the crank arm on the spindle as if I try and reinstall it I suspect having been shoved on a 55Nm if I try and mount it at 40Nm is will be a tiny bit loose . . . . . but leaving the crank arm out of the equation should I back off the tension on the crank arm bolt, as this is only preload it won't effect the crank, should I unscrew it and remount at 40Nm so it's not too stretched and the threads aren't under so much stress ?

Any input appreciated, especially if you are a mechanic.

Concerned of London.

bramp

Where's the 'back it off 1/8th of a turn and spit on it' option?

Out.

Is it square taper or something else? I'd be more inclined to remove and redo but if it's square taper you might have already fubared the crank by pushing its lovely alu edges all up into its chimchiminey.

Or the 'it's fuxxored, I'll take it all off your hands and dispose of it for you' option?

Leave it alone. Not that much over-torqued, or the bolt would have sheared off as it stretched.
Usually a safety factor of 2:1 on such torque apps.
Your hex bit was made from 'cheese-like' material, BTW.

London IMechE prof. / habitual grease munkey!

Where's the 'back it off 1/8th of a turn and spit on it' option?

Out.

That's specifically for carbon:

1) Crank it on until you hear cracking.
2) Keep going a little bit to make sure you can definitely hear something breaking.
3) Then back it off a 1/8th of a turn to make sure it's loose.

Is it square taper or something else? I'd be more inclined to remove and redo but if it's square taper you might have already fubared the crank by pushing its lovely alu edges all up into its chimchiminey.

It's square taper !

Or the 'it's fuxxored, I'll take it all off your hands and dispose of it for you' option?

Two grand (and I'll throw in the broken hex bit).

Leave it alone. Not that much over-torqued, or the bolt would have sheared off as it stretched.
Usually a safety factor of 2:1 on such torque apps.
Your hex bit was made from 'cheese-like' material, BTW.

London IMechE prof. / habitual grease munkey!

That's the kind of news I want to hear ! I celebrate confirmation bias.

The hex bit actually broke, rather than rounded out, I'll take a picture, it was one of those "Oh shit, what have I done, I can't look" moments, lots of grunting, lots of force, then suddenly a loud cracking noise and loss of tension, I was glad it was the hex bit rather than the crank / crank bolt / BB thread or any of the good stuff . . .

Cheese bit !

http://oi44.tinypic.com/2zstt8o.jpg

just a scratch. it'll buff out.

just a scratch. it'll buff out.

T-cut ?

when I buff one out I tend to use this-it's got a deep, rich lustre and a fabulous bouquet.

http://oi44.tinypic.com/2zstt8o.jpg

that last picture is actually quite beautiful
frame it and put it on your wall .. maybe over the toilet pan in the small downstairs bathroom ... next to the escher print

or sell it to some newbie on the forum telling him reassuringly, " of course thats how it's supposed to look " ... then roll your eyes

http://oi44.tinypic.com/2zstt8o.jpg

that last picture is actually quite beautiful
frame it and put it on your wall .. maybe over the toilet pan in the small downstairs bathroom ... next to the escher print

or sell it to some newbie on the forum telling him reassuringly, " of course thats how it's supposed to look " ... then roll your eyes

£120 for a JPEG
£160 for a print of a JPEG
£200 for a photo of a print of a JPEG