How bad of an idea is that? I tighten them everyday about less than a third turn.
maybe teflon tape?

not a bad idea. I just grease mine, but loctite will be good too.

they can rust into place, so grease or loctite to keep the threads from sticking is a good idea.

If your crank bolt is backing out anywhere near 1/3 turn a day I would check the threads of the bolt and crank to make sure that they're not stripping out. I use the blue loctite on my fasteners when necessary, but once any fastener is torqued down it shouldn't back out on its own.

Mike

If it's greased and tightened to the correct torque, it shouldn't be loosening.

Square taper crank?

If that's the case you need new cranks. Once a square taper crank starts loosening up it wallows out the square hole. Once that happens it will never stay tight afterward and (usually the left crank arm) keeps coming off.

And if you have been riding with slightly damaged square taper cranks for some time it is possible the bottom bracket spindle is also slightly rounded out and any new crank you install might round out in short order. When you take off the crank check to see if the spindle looks particularly 'polished' on the edges of the flats - if it does then a new bottom bracket (~$25 for a good one) will save you having to get a third set of cranks in a few weeks. If you change the cranks it is likely that you will need to change the spindle length anyway to keep the chainline straight.

After you get everything replaced then blue loctite on the bolt threads will not hurt, although i just use a healthy amount of thick grease.

The square taper of the cranks and spindle, though, should have NO grease at all... and I have found red loctite applied on all the taper flats (do not put it on the bolt threads) can keep a creaky set of cranks in trouble-free service for years.

Loctite is a bad idea. Gease or even better --an antiseize compound. Lp

I've got the same problem on my Super Sport. I suppose I'll try some loctite, but more than likely I'm looking at a new spindle and crankarms.

it doesn't take much... if the crank loosened off once then it was probably a rounded taper that caused it to loosen. Simply re-tightening and riding might get you home in a pinch but you've got to address the problem, not the symptom.

Blue Loctite won't hurt in that situation. (Blue is medium strength)
My old square taper crank never, ever loosened, that's more than I can say about my Octa-link.

Never re-tighten crank bolts. If a bolt gets loose, remove it, pull the arm and reassemble. Torque the bolt to spec.

I once responded to someone on the forum that maybe loctite would be a good idea for keeping cranks from loosening. Sheldon chimed in and signed off as only he could:
Sheldon "don't need no stinkin' loctite" Brown

Blue loctite is okay. It's designed just for the bolt to keep torque. Red is bad. It is designed for bolts that don't need to be removed.

What with the constant need to tighten the bolt, sounds like the crank arm and spindle are now worn beyond salvation. Try the loctite as a jury-rig, but look to eventual replacement of spindle-bottom bracket.

NO NO NO,

We're talking about the bolts on a square taper crank here. Blue loctite is perfect, and in fact, if you have a factory-assembled bike, you might find that blue loctite was used when it was put together. Campy parts often come with blue loctite already applied to the hardware, need I say more?

Loctite is an antiseize compound.

I think blue Loctite is fine for this application, but only in its anti-seize role. Which is why I would prefer grease or actual anti-seize compound since that will both keep it from rusting in place and also lubricate the threads better and allow proper torquing in the first place.

Given that the torque settings can only be accurate if the component parts are greased, and that grease and Loctite should not be used together, it seems that it would be wise to use grease only.

LOCTITE is a lot of things, from an adhesive to keep screws nuts and bolts from loosening to blue silicone head gasket seal material in a tube. My dad used many of their products as an auto mechanic.

I think there is an issue here with a lot of people thinking pedal spindles rather than crank bolts. If your crank is loosening that fast something is wrong, and you'll probably have to replace the spindle if not the entire bottom bracket, and possibly the crank arms as well. I agree with the above posts that a loosening part should be completely removed before being torqued back down.

This is correct. Loctite is a name brand of many things. You can use loctite anti-seize to prevent seizing as well as using the 2-octylcyanoacrylate which is an adhesive (super glue). They have different levels of of adhesives for many household and automotive applications.

I hardly think that my cranks are loosening. A third turn is quite a small amount and I believe I have over torqued the bolts. How the hell would I measure torque on a #8 hex?
I am really bearing down to tighten them that bit as they are newly installed and I am fiddling w/ them.

What kind of risk is run by using grease and Loctite together? I just installed a Campy crankset last night. I noticed the blue Loctite already on a few of the threads of the crankbolts, but under the impression that threaded items ought to be greased before tightening, I added a modest amount of polylube before putting the crankbolts in. Afterwards (LOL) I noticed the part of the Campy manual where it says "NEVER use grease" on the crankbolts. Uh-oh... Do I want to pull the bolts, degrease, apply Loctite, and start over??

You can accurately torque anything that you can buy a socket for, and you can buy a socket for an 8mm allen head bolt.

If you over-torque the cranks then you will 'stretch' the inside of the crank taper, which is as bad as riding with the cranks loose. Check the back of the spindle-hole in the crankarm to see if it is flat, or if the spindle has caused the edges to flare outward a bit. If the back of the hole is not completely flat then you have damaged the cranks.

In extreme cases, overtorquing can stretch the taper so much that the crank bolt will bottom out on the bb spindle before actually securing the crank.

Greasing the spindle or crank taper makes damage from over-torquing much more likely.

Have you confirmed that the bolts are actually backing out? (mark the head with some nail polish or similar) What could be happening is that when you ride the cranks 'squirm' up the tapers a bit, so the bolts naturally seem looser even though they haven't actually turned -- this is to be expected and nothing to worry about. If this is happening and you keep on tightening the bolts you will destroy the crank.

Recommendation: REMOVE the cranks completely, lightly grease the tapers and reinstall to appropriate torque. Use loctite only if you've confirmed that the bolts are backing out.