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Old 08-03-08, 10:02 AM   #1
YungBurke
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Lock Tite?

A couple of the threaded parts of my vintage roadie are always coming unscrewed. Is it ok to use Locktite on the Headset screws and crank screws? If so what composition do you guys like for bikes
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Old 08-03-08, 10:17 AM   #2
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If your headset and crank bolts are coming loose, it could be a lack of torque.

Although many wrenches will tell you to never use loctite, many manufacturers use it on OEM parts. Who ya gonna believe? Use blue Loctite 242 if in doubt. It allows fastener removal with hand tools and won't harm a thing.
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Old 08-03-08, 10:17 AM   #3
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Locktite should never be needed if the bolts are torqued properly when initially installed. This is particularly true of crank fixing bolts. The tightening torque is very high (25 - 35 foot-pounds) and if done right they will never loosen unintentionally. If the bolts continually loosen, they were never installed correctly and, if the crank arms have come loose on a ride, it's very possible they are damaged beyond repair.
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Old 08-03-08, 10:36 AM   #4
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Originally Posted by HillRider View Post
Locktite should never be needed if the bolts are torqued properly when initially installed. This is particularly true of crank fixing bolts. The tightening torque is very high (25 - 35 foot-pounds) and if done right they will never loosen unintentionally. If the bolts continually loosen, they were never installed correctly and, if the crank arms have come loose on a ride, it's very possible they are damaged beyond repair.
How would I know?
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Old 08-03-08, 02:22 PM   #5
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How would I know?
Remove the crankarms and look down the hole in the arm. It should be a perfectly square tapered hole. The flat sides of the hole should be pristine with no deep gouges. If it's not, you won't have a nice mating surface for the crank and it won't stay put. Most of the time, you have only one chance to install the crank correctly and that's the very first time. As soon as it comes loose the 1st time, you MUST stop riding and re-install it correctly to the proper torque of 30-35lb*ft. If not, you'll gouge out the square taper and no amount of tightening or using thread-lockers will hold the crank on.
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Old 08-03-08, 02:39 PM   #6
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Adding to Danno's post....

Some bruising of the taper may not be noticable to the naked eye but it can still be enough to mess up the crank arm and make it work the bolt loose. He's right in that you can't afford to mess up even one time. If there's obvious deformation or galling (torn out tracks and bumps in the metal on the inside of the crank's square hole) then the arm is shot. But even a small indescernable deformation will allow the arm to not seat solidly and let it pivot when you're pedalling. Even a very small amount will work the bolt loose and lead to further damage as the crank walks out.

Any accurate taper will push on easily and then with even the first couple of lbs of direct pressure lock itself into immobility with the axle. You can test this yourself by cleaning and lightly oiling the axle and crank hole and then push it on by hand with a firm push but do not use the bolt, just hand pressure. Then try to twist and pivot the arm. If you can feel any twisting or pivoting motion in any plane then the crank arm is shot and should be replaced since it's obviously making the bolt come loose. For the final install the taper and socket must be greased to avoid the aluminium galling on the steel. I also grease the threads of the bolt as well as under the head so it lets the bolt screw in easier and slip against the crank arm to avoid galling.

If your stem locking bolts are coming loose I suspect it's because you're not torqueing them in stages like you should. Even with only a two bolt stem lock the bolts should be brought up to matching torque values in stages to allow for the stem stretching and seating. You'll feel this because you'll torque one bolt, then the other and when you come back to the first it will be easier to move to the next torque value. The idea is to sneak up on the final correct value in about 4 to 6 stages. Same with loosening them. It's best to loosen one a 1/4 turn, then the other and work both loose 1/4 turn at a time for the first couple of turns. If you back off one all the way first it leaves the second with a LOT of torque and that can lead to premature wear of the threads.

On a 4 bolt stem cap this is even more important to make sure you tighten them using an X pattern so all the bolts are equally loaded in all 4 corners and come up to the final torque equally to avoid a twist in the cap.

I've gotten bolts with a dab of dry threadlock but I grease them anyway. Around here if I don't it'll be rusted pretty soon. I've never had a greased bolt in any application come loose as long as the parts mate correctly and I sneak up on the matching final torque values for multi bolt situations.
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Old 08-03-08, 02:57 PM   #7
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Blue Loctite isn't going to "hurt" anything.
http://www.loctiteproducts.com/produ...ID=10&SubID=48
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Old 08-03-08, 03:25 PM   #8
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Originally Posted by YungBurke View Post
A couple of the threaded parts of my vintage roadie are always coming unscrewed. Is it ok to use Locktite on the Headset screws and crank screws? If so what composition do you guys like for bikes
You don't need loctite for either of these applications.
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Old 08-03-08, 04:21 PM   #9
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Well maybe there is another place Im looking, but my cranks have splines, not square acceptors.
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Old 08-03-08, 04:32 PM   #10
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Ah.... Try totally cleaning the splines in both the BB and the crank. Like wipe out the grease and then wash it with a toothbrush and some mineral spirits. Especially the BB splines. When dry inspect VERY carefully for debris.

I had a persistent and horribly annoying creak on a Shimano Octalink BB and Specialized Strongarm crank setup. I demounted the cranks, wiped them off, they looked fine and re-greased and the creak was still there despite tightening. Also I found that the bolt didn't walk out it was somewhat looser when I went back to it a few weeks later to finally have at it again.

What I found with a thorough cleaning and inspection was a tiny little shard of metal jammed down in one of the rounded ends of a spline in the BB. I had to pick it away with a scriber. I re-greased, remounted and it has been fine ever since. These splined BB setups seem to be very touchy for stuff like this.
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Old 08-03-08, 05:35 PM   #11
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Quote:
Originally Posted by YungBurke View Post
Well maybe there is another place Im looking, but my cranks have splines, not square acceptors.
These cranks (Octalink or ISIS) will tolerate a bit of looseness once or twice but you can still distroy them by riding with the arms loose. Again, the specified installation torque is very high and, if done properly, they won't come loose. Loctite won't "hurt" anything but it won't substitute for doing the job right the first time.
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