DiabloScott <
[email protected]> wrote in message news:<
[email protected]>...
> OK, sorry for being such a dunce but what exactly does Locktite *do*? Is it some kind of glue?
> Does it increase the amount of loosening torque required by a factor of 2? 3? 10? 100? And what
> are the differences in the various types available?
>
> I don't think I'd trust it on a fixie without a lockring based on everything I've read here and
> elsewhere and it seems like this thread has run its course but I would like to understand
> Locktite better.
>
> Where else would it be used on a bike? Bottom bracket cups? I've done just about every mechanical
> thing you can do with a bike and have never used Locktite.
>
Dear Diablo,
I almost looked things up, but decided that would be the coward's way out.
My guess is that the goo is a void-filler and feeble adhesive with various grades of stickiness.
By filling minute voids and providing a bit of stickiness, it reduces the danger of threaded
fasteners working loose under vibration and when tension varies because of mechanical changes like
metal parts expanding and contracting with heat cycles and gaskets compressing under load between
metal parts.
Proper tension and thread design achieve the same effect--that's what the right nuts and bolts do
with the help of washers.
The most adhesive grades of Loc-tite can set to glue-like stiffness and provide enormous
resistance to turning--the trick usually mentioned here on rec.bicycles.tech is to heat the part
and soften the goo.
The resistance may be partly due to the goo expanding slightly while setting and therefore gripping
the bolt inside the nut, but for all I know the stuff may contract.
In either case, the goo adds friction and resistance to turning because it fills in the tiny voids
between the bolt and nut threads.
A bare thread-to-thread contact has only the friction where metal touches metal, with no friction
where the metal surfaces fail to meet.
Threads liberally smeared with Loc-tite have most of these voids filled with long ribbons of rubbery
goo under compression wherever the metal failed to touch. Press two flat pieces of metal together
and try to turn them--they turn easily. Now sandwich a rubber mouse pad between them and feel how
the increased friction resists turning.
Despite what we see on the outside, where the goo often sticks to broad metal surfaces, there's not
likely to be much actual glue-like adhesion on what are fairly polished metal threads, usually so
oily that not much really sticks to them.
When Loc-tite "sticks," it's usually just hanging in a well-moulded embrace to a metal shape. A
screw with a smooth upper shaft will illustrate this. The ring of Loc-tite on the threaded section
seems to grip, but so does a tight nut, which is hardly "sticking" like glue. The same ring of Loc-
tite around the smooth metal shaft has no irregular shape to mould to and is easily moved. And up
where the smooth shaft joins the screw head, the Loc-tite may find some irregularities to cling to
and becomes a little stubborn again.
While the worst Loc-tite can help a screw or bottom-bracket put up a fierce fight against a
screwdriver or a bottom-bracket pin-spanner, it's unlikely to be a match for stress faced by the lock-
rings in this thread. I suspect that they work loose as a matter of design. A fixed-gear bike
applies force both ways, so it may work a threaded fastener loose, Loc-tite or not.
Think of pedals, which have left and right threads to prevent loosening under the torque of normal
pedalling. I don't recall any posts about pedals working loose on fixed-gear bikes, but the reason
is probably that the vast majority of fixed-gear pedalling is in the normal direction and tends to
tighten things, while only the braking at the end of a long session of forward pedalling tends to
loosen the pedals.
Cynically speaking, the primary purpose of Loc-tite is to mark threaded objects that we fear may
loosen. When reluctantly applied by the factory, it serves to highlight poor design.
Let's hope that my speculation provokes some better-informed comments on the stuff. When I looked
just now, I found that I still have a nearly thirty-year-old tube of the stuff, so it may not be
quite as necessary as I thought when I was a teen-ager.
Now I'll search and find out how it's really spelled.
Carl Fogel
