Moe Zhoost

So last Sunday morning, I was riding a rather leisurely route along a local MUP that runs from the downtown area of my city south to some rather rural areas with infrequent road crossings. It was in such an area that I saw up ahead a dismounted cyclist walking toward me. As I got closer I got the sense that he was looking for something. When I asked him if he needed any help, he held up his left side crank saying that he was looking for the bolt. Well, since this was on the non-paved part of the MUP, which would have made it difficult to see a bolt <and> it was likely that the bolt had been lost at anytime within the last 50 miles <and> I didn't have a spare bolt <and> neither of us had a wrench to install a bolt anyway, I had pretty much exhausted my ability to help. The square taper on the crank was tweaked a bit so jamming it back on with some taps from a handy branch was iffy. I asked him if he had a phone to call for help (yes), told him which road crossing was closest to our position, wished him luck, and then just left him there.

Worse for him, but I am still bummed that I couldn't help.

Retro Grouch 

A fairly common problem.

The torque spec for square taper crank arm bolts is around 30 ft/lbs. That's quite a bit more than I would use if left to my own judgement. If you're using a 6 inch long allen key to tighten that bolt you might get there - but I seriously doubt it.

Sangetsu

I've never lost a crank bolt, but I have had them loosen up, causing a clicking sound in the crank. If it gets to the point that the cranks start clicking, they might need replacing (as I found out the hard way). Now I have only one bike with a square taper crankset, and I have the proper tool to tighten it regularly.

bulldog1935

these specs are in lb-in, but yes, it would be tough to get there with a 10" breaker bar, and always better to use a good torque wrench

Torque Specifications and Concepts | Park Tool
there are specific torque requirements from different makers
Crank bolt (including spline-type cranks and square-spindle cranks) 305–391
Bontrager® 310–380
Campagnolo® 312–324
FRA® (M8 bolt) 304–347
FRA® (M14 steel) 434–521
Race Face® 480
Syncros® 240
Truvativ® ISIS Drive 384–420
Truvativ® square type 336-372
White Ind® 240–300
Jan Heine recommended 250 lb-in for T/A

AlexCyclistRoch

If you are using a common style bolt, always, ALWAYS install the washer. And torque the ling bejeezus out of it, especially if you are using one of those T-handle wrenches.

corrado33

I tighten the crank bolts on square tapers pretty much until the wrench causes pain in my hand. Being a 150 lb gorilla, that seems to be close enough to the spec that they never come off. (I've never had a crank bolt come off.)

Crank bolts, like cassette lockrings, have a much higher torque spec than most people would guess.

Retro Grouch 

Yeah, but too much is bad too. I've also seen cranks that cracked out at one of the corners of the square hole.

faulker479

I had one that would come loose even after putting the gorilla touch on it. Neither the bolt nor the bottom bracket were stripped so I put some red locktite on it and that solved the problem.

jefnvk

I torque the F out of them, to the point where I generally destroy my knuckles on the flailing pedals when the bolt finally goes loose taking them off. Never had one seem remotely loose the next time I removed it.

Cheddarpecker

Funny, because with this in mind, and the size of the hardware, I always figured on about 25 ft.lbs max. The list above is all fairly close to that. My torque wrench is half inch, doesn't register below 20 lbs, and only comes out for crankshafts, heads, and the occasional non adjustable valvetrain.

Grand Bois

Try to crack a crank that way. I'll bet that the 8mm bolt breaks first.

Retro Grouch 

So what do you think made it crack?

WizardOfBoz

Yeah, I ruined a Campy Nuovo Record non-drive-side crank arm because I failed to torque the bolt and rode it loose. Sigh.

I did go out and get a good torque wrench to torque the chainring bolts on my Dura-Ace 11spd chainring. Had to set it up with a 1/4" ratchet drive 1/4" hex socket, then the approriate torx (T-30?) 1/4 hex bit. But the chain ring doesn't creak anymore.

That's one thing I value: my bike running absolutely quietly.