H3llM4rine

I'll tighten my cranks as much as possible, and those things just won't stay tight. I can re-tighten them once a week. They're square-taper interface.

I'm honestly considering just getting an ISIS BB and crankset. Any suggestions for a cheap pair of those, as well?

DMF 

They must be replaced. By riding them when loose, someone has flared the sockets on the arms and they will henceforth and forevermore work themselves loose. Over tightening the bolt will only break it.

Why ISIS? It is only an interface specification and both good and lousy BBs use it.

Since you don't tell us anything about the bike, we can't make a recommendation.

New Posters - please READ THIS

AndrewP

Time for new cranks. Square taper ones are reasonable priced, and work well. Just make sure the BB taper and crank taper are the same standard.

H3llM4rine

Whoops! I meant to say more about the bicycle.
I'm a heavy guy, and I ride a fixed-gear. I'd like very durable cranks.

The cranks are two weeks old. The day I put them on, I put them on very tightly so that this wouldn't happen, but it still is. Could it be the BB bolt?

demoncyclist

Well, either you really didn't tighten them to the proper torque specs, or you overtightened them and stretched/stripped the threads on the bolt or the BB spindle. A torque wrench is your friend.

H3llM4rine

I guess I'll just take it to the LBS and have them tighten them up for me. In the mean time, I'll be looking for a torque wrench.

Thanks!

demoncyclist

Even they can't help you now. Once you ride them loose, the square hole in the crank gets rounded out. They are hosed and need to be replaced.

H3llM4rine

Well, actually, the looseness is not on that axis. I'm sorry, I'm doing a horrible job being descriptive today.

They become loose side-to-side, not front-to-back. I can feel them move ever so slightly if I stand on the pedal and let it go over the top I can feel it move slightly outwards.

DMF 

What gearing do you need? What size is the hanger tube? (probably 68mm, but one never knows..)

Two weeks old to you? Or two weeks out of the shipping box? I suspect they were fubar when installed.

DMF 

You're right. I don't get it. Cranks go in a circle. Side-to-side and front-to-back are the same thing.

Or do you mean axially vs. radially?


Let's boil it down to this: Do you need to re-tighten the bolt because it worked loose?

DannoXYZ 

Exact how tight did you install them? Did you install them on dry spindle? Oiled or greased? Without an exact torque-figure, they could've been put on too tight or too loose; both of which will result in the crankarm falling off later.

Here's a list of common torque-specs from Park Tool. Square-taper cranks typically require 25-33 lb*ft of torque. This is impossible to do with little L-shaped allen-keys and really requires an automotive-style ratchet-wrench and socket. Preferably one with an 18" handle or longer to achieve the required torque.

Don't worry, you're not alone:

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operator

You might want to read the entire thread before replying. He's implying that the BB is loose, not the cranks.

DMF 

I dunno. This statement seems pretty unambiguous to me:

operator

You will be buying yourself a new problem by going ISIS, there are limited crankset choices and there are limited bottom bracket choices. Stick with the square taper or go with external.

DannoXYZ 

Maybe... loose crankarm bolts would result in both axial and radial play. I wonder what he's tightening once a week, and how is he doing it.

operator

I find it frustrating that threads like this is a 0.5 second solve in real life.

DannoXYZ 

Well, he is taking it to a shop.

wrk101

I'm betting on a bb issue, but who knows? Taking it to a shop is a great idea.

blasternot112

I get this issue all the time, most common cause is improper tightening in the first place
-this loosens them up
-this rounds them off
-this makes them worthless
-this means you need to replace crankarms

...typically

JohnDThompson 

Sounds to me like the bottom bracket is the issue, not the crank.

electrik

Before you take it to a shop, get some loctite 243(service removable) slather some on the bb spindle and then put some on the bolts... for god's sake don't reef on the bolts, you just want the taper to interface be snug... we're talking 15nm or less..

let the loctite cure overnight, try em out.

P.s. don't use anything stronger otherwise you'll need a hacksaw to get them off!

operator

Do not do this.

Bolts and spindles do not need loctite. Grease if anything. Taper is debateable, I do because seized cranks are annoying.

electrik

Why shouldn't he? I did it and my crank arm hasn't come off by itself for 8 months...

LarDasse74

Grease on the bolt threads.
RED locktite on the taper.
But his cranks are pooched.

vettefrc2000

You can also use brass shim stock and then torque.