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Loctite on cogs...why???(7 posts)

Loctite on cogs...why???Djudd
Nov 16, 2002 6:48 PM
In another fixed gear discussion group someone was asking how to loosen a cog fixed with Loctite. The answer was heating the cog evenly with a torch. My question was why would you put loctite on a cog? There is a proper and intelligent way to lock a cog in place. Loctite seems unnecessary and even stupid. Am I wrong here, is there a reason to do this?
re: Loctite on cogs...why???Dad Man Walking
Nov 16, 2002 8:44 PM
The cog wants to tighten with the pressure of forward pedaling (it's a right-hand thread thing). If you really stomp in the backwards direction (to slow down), you can loosen the cog. Purpose-built track hubs have a lock ring to prevent this, so loc-tite is not needed. If you have converted a road hub and can't use a lock ring, a little loc-tite adds a lot of peace of mind.
I never use Loctite on my fixed cogs.eddie m
Nov 17, 2002 9:08 AM
Blue Loctite does not need to be heated to remove the cog. It works great to keep bolts from backing out due to vibration, but I think blue Loctite actually makes removing the cog easier by lubricating the threads and by preventing corrosion. I'm not sure what effect it would have in actual use with the fixed gear.
There are also other Loctites (red or green?) that are stronger but need to be heated to disassemble, but I'm not concerned enough about my cog backing out to deal with the heat required to disassemble it.
Proper track hubs have a lockring ...Humma Hah
Nov 17, 2002 9:37 AM
... that tightens on a slightly smaller set of threads that screw on the opposite direction to the cog. But many fixie conversions just use old 6- or 7-speed hubs that are intended to screw on freewheels, and lack the locking ring threads. It is on these hubs that the less brave souls use Locktite. If you're in the habit of vigorous braking with the pedals, I've seen posts here from folks who HAVE spun a non-lockringed cog loose, and this is possible in some track riding styles. On the other hand, a street fixie equipped with brakes and ridden moderately may never need Locktite, even with no lockring.
Proper track hubs have a lockring ...eddie m
Nov 17, 2002 11:37 AM
but I use a six speed road hub with a bottom bracket lockring on the fixed gear. I've never had any trouble with it. I'm not convinced loctite would prevent that from backing out, but if anyone has some real data on that issue I would like to see it. Maybe I don't have much trouble with it because I'm not very strong anymore.
A lot of folks have posted various places ...Humma Hah
Nov 17, 2002 7:01 PM
... that, like you, they've had no problems running the freewheel threads with no loctite. Every now and then you'll encounter a poster who HAS had one unscrew, to their great alarm.

In my case, I did some track training a few years ago. They didn't waste much time running us gently around the velodrome, but cranked us up to high speed fairly quickly. How well I remember my first standing sprint up to a race pace, and how I forgot for a split-second what I was riding as I sat down -- I tried to coast. Sumbitch tried to shoot me to the moon! The rear wheel skipped a few times on the track surface.

Later, we did a reverse paceline exercise. Riders came off the back of the paceline and sprinted to the front to take their place. This requires quickly getting rid of all that kinetic energy via backpedaling, and the forces on the pedals were simply stunning ... this was essentially panic braking with no brakes.

Either of these situations might be enough to wrench loose an unlocked cog. However, both are the result of the insanity of track ... a bike equipped with brakes and not sprinted like a maniac before the rider quite gets the hang of not being able to coast, or run thru counter-intuitive bass-ackwards exercises, might NEVER encounter such forces.
Had one back off, but . . .micha
Nov 18, 2002 2:50 AM
, , , as a result of my own carelessless. I screwed a cog on my road hub, hand-tight only. My thinking was "the first hill will tighten it so it'll never come loose." Well, before the first hill ever came, I back-pedaled gently rolling up to a stop sign and the cog started backing off. You'll know immediately when this happens - the bike changes from fixed to freewheel in an instant. My immediate reaction was to stomp the pedals hard (ran the stop sign).The cog tightened back up, Don't know how I knew to do this - never had time to "think" about what to do.

So - when putting on a cog without a lockring, climb a hill or do a sprint immediately after that. Or get a chainwhip.