Subject: 8d.2   Chain cleaning and lubrication; wear and skipping
From:  Jobst Brandt <jobst.brandt@stanfordalumni.org>
Date: Tue, 13 Mar 2007 17:13:21 -0700

Chain wear and care evokes a perpetual discussion, especially among
new bicyclists who are unhappy with this dirtiest part of the bicycle.
This raises the principal question, of whether there is a best (and
cleanest) way to care for a chain or whether the chain should just be
discarded when it gets grimy.  Among several ways to take care of a
chains, some traditional methods are the most damaging while others
work to prolong chain life.

A myth that is difficult to dispel is the story that grease on a new
chain, fresh out of the package, is not a lubricant but rather a
preservative that must be removed.  This piece of bicycling myth and
lore thrives despite its illogic.  The largest chain customers are
bicycle 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 of it on a chain, the excess can be wiped off with a rag.

Riders often speak of "chain stretch" a technically misleading and
incorrect term.  Chains do not stretch, in the dictionary sense, by
elongating the metal by tension.  Chains lengthen because their hinge
pins and sleeves wear.  Chain wear is caused almost exclusively by
road grit that enters the chain when it is oiled or when riding in wet
weather.  Grit adheres to the outside of chains in the ugly black
grime that can get on ones leg, but this external grime has little
functional effect, being on the outside where it does the chain no
harm.

The black stuff is oil colored by steel wear particles that come from
pin and sleeve wear, the wear that causes pitch elongation.  The wear
rate is dependent primarily on how clean the chain is internally
rather than visible external cleanliness that attracts most attention.

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).
Oiling a dirty chain washes the adhering road grit into the chain
where it can grind away on the load bearing hinges.

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

This means the chain should be cleaned of grit before oiling, and
because this requires submerging the chain in solvent (kerosene,
commercial solvent, or paint thinner), it must be taken off the
bicycle.  Devices with rotating brushes, that can be clamped on the
chain while 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.

Many non-petroleum based solvents are offered through bicycle
retailers and these have the advantage that they can be rinsed off
with water.  The chain must be dried before lubricating it after that
because otherwise a rust forming emulsion will develop in use.

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.
Fortunately after riding in heavy rain, the chain is fairly clean and
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 chain lubricant, but it
evaporates as soon as the road dries.

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.  Most Accelerated drying methods by
heating 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.  30W 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 its 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 (as on motorcycles)
are well protected against lubricant depletion because both ends are
covered by closely fitting side plates with some motorcycle chains
having 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 so the pins and rollers gall easily
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 wear depends almost entirely on cleanliness and lubrication
rather than being 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 thousands of miles while exposed rear
chains must be replaced far more often.

The best way to determine whether a chain is worn is by measuring its
length.  A new half inch pitch chain will have a pin at exactly every
half inch.  As pins and sleeves wear, this pitch increases, so that
more load bears on the last tooth of engagement as the chain rolls off
the sprocket, thus 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 roughly one percent, twice
the sixteenth inch limit that is a prudent time for a new chain.

Chain Sprockets do not change pitch when they wear, only their tooth
form changes.  The number of teeth and base circle remain unchanged on
a worn sprocket.  What changes is the diameter at which the lengthened
(worn) chain bears on the sprocket teeth, making wear pockets at a
larger diameter than a new chain requires.  In practice, this amounts
to a change of pitch (or pitch circle), because the chain will no
longer ride in the original valleys between the sprocket teeth.

A new chain often will not freely engage a worn rear sprocket under
load even though the sprocket root diameter has the same pitch as the
chain.  Under tension, the incoming chain rides in the pockets worn by
an elongated chain that are higher on each tooth (a larger pitch
diameter) than a new in-pitch chain requires.  This wear occurs
because a worn chain rides high on the teeth.  A new chain with
correct pitch cannot enter into engagement because its rollers ride in
the wear pockets made by a chain with a larger pitch.

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 chain enters with drive tension.

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.  Chain suck occurs less
with road racing bicycles, that experience a noisy disengagement
instead.