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Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Section - 8d.2 Chain cleaning and lubrication; wear and skipping

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Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Previous Document: 8d.1 Lubricating Chains
Next Document: 8d.3 Adjusting Chain Length
See reader questions & answers on this topic! - Help others by sharing your knowledge
Date:    Thu, 10 Jan 2002 17:40:52 -0800 (PST)

Chain wear and care evokes never ending discussions, especially for
new bicyclists who are not happy with this dirtiest of bicycle parts.
This leads to the first problem, of whether there is a best (and
cleanest) way to care for a chain.  There are several ways to take
care of a chain of which some traditional methods are the most
damaging to the chain and others work to prolong its life.

That grease on a new chain, fresh out of the package, is not a
lubricant but rather a preservative that must be removed, thrives in
bicycling myth and lore.  This is nonsense because chains are used as
they are by manufacturers who ship bicycles ready to use.  They can
order chains with any desired lubricant and this is what they use.  If
there is too much on the chain, it can be wiped off.

At the outset the term "chain stretch" is technically wrong and
misleading.  Chains do not stretch, in the dictionary sense, by
elongating the metal through tension.  They lengthen because their
hinge pins and sleeves wear which is caused almost exclusively by road
grit that enters the chain when oiled.  Grit sticks to the outside of
a chain in the ugly black stuff that can get on ones leg, but external
grime has little functional effect, being on the outside where it does
the chain no harm.  Only when a dirty chain is oiled, or has excessive
oil on it, can this grit move inside to causes damage.  Commercial
abrasive grinding paste is made of oil and silicon dioxide (sand) and
silicon carbide (sand).  You couldn't do it better if you tried to
destroy a chain, than to oil it when dirty.

Primitive rule #1: Never oil a chain on the bike.

This means the chain should be cleaned of grit before oiling, and
because this is practically impossible without submerging the chain in
a solvent bath (kerosene or commercial solvent), it must be taken off
the bicycle.  Devices with rotating brushes, that can be clamped on
the chain on the bicycle, do a fair job but are messy and do not
prevent fine grit from becoming suspended in the solvent.  External
brushing or wiping moves grit out of sight, but mainly into the
openings in the chain where subsequent oiling will carry it inside.

Do not use gasoline because it is explosive and contains toxic light
petroleum fractions that penetrate skin.  Removing the chain from the
bicycle isn't always possible.  There are times (after riding in the
rain) when a chain screams for oil and good cleaning is impractical.
In that case rule #1 may be violated for humanitarian reasons.
However, only an internally clean chain squeaks, so it isn't as bad as
it sounds.  Also, water is a moderately good lubricant, but it
evaporates soon after the rain stops.

Removing solvent from the chain after rinsing is important.
Compressed air is not readily available in the household nor is a
centrifuge.  Manually slinging the chain around outdoors works best if
the chain is a closed loop but without pressing the pin completely in.
The other way is to evaporate it.  Accelerated drying methods by
heating should be avoided, because they can be explosive.

Lubricating the chain with hot 90W gear lube works but it is also
efficient fly paper, collecting plenty of hardpack between sprockets
and on the outside of the chain.  Motor oil is far better, but
motorcycle chain and chainsaw lubricants are better yet, because they
have volatile solvents that allow good penetration for their
relatively viscous lubricant.  Paraffin (canning wax), although clean,
works poorly because it is not mobile and cannot replenish the bearing
surfaces once it has been displaced.  This becomes apparent with any
water that gets on the chain.  It immediately squeaks.

Swaged bushing chains

Sedis was the first with its Sedisport (five element) chain to
introduce swaged bushings, formed into the side plates, to replace
(six element) chains with full width steel bushings on which the
rollers and pins bear.  Although stronger and lighter than prior
chains, the five element chain achieves its light weight at the
expense of durability.  These chains, now the only derailleur chains
available, have only vestigial sleeves in the form of short collars on
the side plates to support the roller on the outside and the link pin
on the inside.  This design is both lighter and stronger because the
side plates need not have the large hole for insertion of sleeves.

Pins inside full bushings of (six element) chains were well protected
against lubricant depletion because both ends were covered by closely
fitting side plates.  Some motorcycle chains have O-ring seals at each
end.  In the swaged bushing design there is no continuous tube because
the side plates are formed to support the roller and pin on a collar
with a substantial central gap.  In the wet, lubricant is quickly
washed out of pin and roller and the smaller bearing area of the
swaged bushing for the pin and roller easily gall and bind when
lubrication fails.  Although this is not a problem for this type of
chain when dry it has feet of clay in the wet.

Chain Life

Chain life is almost entirely a cleanliness and lubrication question
rather than a load problem.  For bicycles the effect of load
variations is insignificant compared to the lubricant and grit
effects.  For example, motorcycle primary chains, operated under oil
in clean conditions, last as much as 100,000 miles while exposed rear
chains must be replaced often.

The best way to determine whether a chain is worn is by measuring its
length.  A new chain has a half inch pitch with a pin at exactly every
half inch.  As the pins and sleeves wear, this spacing increases,
concentrating more load on the last tooth of engagement, changing the
tooth profile.  When chain pitch grows over one half percent, it is
time for a new chain.  At one percent, sprocket wear progresses
rapidly because this length change occurs only between pin and sleeve
so that it is concentrated on every second pitch; the pitch of the
inner link containing the rollers remaining constant.  By holding a
ruler along the chain on the bicycle, align an inch mark with a pin
and see how far off the mark the pin is at twelve inches.  An eighth
of an inch (0.125) is one percent, twice the sixteenth limit that is a
prudent time for a new chain.

Skipping Chain

Sprockets do not change pitch when they wear, only their tooth form
changes.  The number of teeth and base circle remain unchanged by
normal sprocket wear.

A new chain often will not freely engage a worn rear sprocket under
load even though it has the same pitch as the chain.  This occurs
because the previous (worn and elongated) chain formed pockets higher
on each tooth (a larger pitch diameter) than an in pitch chain
describes.  This wear occurs because a worn chain rides high on the
teeth.  A chain with correct pitch cannot enter the pockets when its
previous roller bears the previous tooth, because the pocket has an
overhang that prevents entry.

Without a strong chain tensioner or a non derailleur bicycle, the
chain has insufficient force on its slack run to engage a driven
sprocket.  In contrast, engagement of a driving sprocket, the crank
sprocket, generally succeeds even with substantial tooth wear, because
the drive tension forces engagement.

However, worn teeth on a driving sprocket cause "chainsuck", the
failure of the chain to disengage.  This occurs more easily with a
long arm derailleur, common to most MTB's, that is one reason this
occurs less with road racing bicycles, that experience a noisy
disengagement instead.

In contrast a worn chain will not run on a new driving sprocket.  This
is less apparent because new chainwheels are not often used with an
old chain.  In contrast to a driven (rear) sprocket the chain enters
the driving (front) sprocket under tension, where the previous chain
links pull it into engagement.  However, because a used chain has a
longer pitch than the sprocket, previous rollers bear almost no load
and allow the incoming chain link to climb the ramp of the tooth, each
successive link riding higher than the previous until the chain jumps.
The pockets in a used sprocket are small but they change the pressure
angle of the teeth enough to cause skipping.

Jobst Brandt      <jobst.brandt@stanfordalumni.org> 

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Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Previous Document: 8d.1 Lubricating Chains
Next Document: 8d.3 Adjusting Chain Length

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