Newsgroups: rec.motorcycles
Subject: rec.motorcycles FAQ of 93.01.01    (Part 3 of 5)
From: dave.williams@chaos.lrk.ar.us (Dave Williams) 
Date: 10 Jan 93 18:41:00 GMT
Reply-To: dave.williams@chaos.lrk.ar.us (Dave Williams) 
Distribution: world
Organization: The Courts of Chaos * 501-985-0059 * Public Access Usenet


(seems the first send got truncated)
                          =====================

Q:  I've been looking to buy a [brand and model name not important].
    Several people have told me those bikes have troubles with second
    gear.  How can I tell if this one is OK, and why do they have this
    problem?

A:  Second gear problems are the most common of all.  They tend to be
    worse on high-power machines.  Typically, the rider doesn't get
    the gear all the way into engagement, and it pops out under hard
    acceleration.  This typically rips metal off the engagement
    surfaces, making it that much easier to pop out the next time.
    Eventually the machine will pop out of gear under acceleration.

    Incorrectly adjusted clutches, careless shifting, and shifting
    without the clutch can all cause second gear problems. The fact
    that you could shift your dirt bike without the clutch is not
    relevant; your dirt bike probably doesn't weigh 550 pounds, run
    on pavement, and have a fat tire on the back.

                          =====================

Q:  My motorcycle seems to use up chains pretty fast.  How can I tell
    the difference between a good chain and junk chain?

A:  I wrote an article for Australian Motorcycle News which covered
    this subject in detail.  I've reproduced it here:

    Years ago chains were considered disposable items. I remember
    scraping up money for the spring chain and sprocket ritual every
    year when I was in high school. Sometimes the chain wouldn't make
    it through the summer, even with fanatic oiling. Every T-shirt I
    owned had an oil stripe down the back on the left, much to my
    mother's dissatisfaction. I once had a two-month-old chain on my
    175 Kawasaki snap while going 50mph. The broken chain wrapped
    itself around the swingarm and locked the rear wheel solid,
    whereupon the rear wheel decided it would lead for a while. By some
    miracle I came to a halt still vertical, but I have had a paranoid
    distrust of chain drive ever since.

    Now what, might you ask, would cause a chain to break like that? It
    was properly lubricated, adjusted, and running on the correct size
    (new) sprockets. Chances are that the local motorcycle shop had
    sold me some ordinary industrial chain instead of motorcycle chain.
    Such unscrupulous dealings were far more common years ago than they
    are now. A real chain might cost $30 then, but farm machinery chain
    sold for a little over a dollar a foot. What's the difference?

    In its simplest form, the roller chain consists of side plates,
    pins, and rollers. When properly lubricated, this type of chain
    will perform acceptably for most engineering purposes.
    Unfortunately, proper lubrication consists of an oil fog or bath
    and freedom from dirt, both conditions unlikely on a motorcycle.
    Twenty years ago some machines still came with enclosed chains, but
    the enclosed chain died away not because of styling, but because it
    was a tearing pain in the arse to service the chain or rear wheel
    with the bulky (and oftimes leaky) enclosure in the way.

    The oilite-bushed chain assisted the enclosed chain to oblivion. A
    porous bushing was pressed into the roller and rode on the pin.
    This porous bushing was impregnated with lubricant and would absorb
    chain lube too. With a moderate amount of maintenance the bushed
    chain was satisfactory if not perfect. Since the mid-1960s all
    "real" motorcycle chain has been of the bushed type. The chain that
    caused my hair-raising ride was likely of the previous type.

    In the mid-1970s the "O-ring" chains came into use. These were
    bushed chains using O-ring seals to keep the lubricant in and dirt
    and water out. They represent the latest word in drive chain
    design, being reliable, long lasting, and low-maintenance. Indeed,
    when run on plastic sprockets, the O-ring chain may need no other
    lubrication during its operational lifetime.

    Modern motorcycle chains come in two basic types - those which are
    endless, and those which use master links. Endless chains came
    about when engineers realized that most catastrophic chain failures
    ocurred at the master link. By eliminating the master link,
    reliability could be enhanced. Unfortunately, endless chains can
    cause a problem if the sprocket sizes have been changed much; if it
    is too long or too short, nothing can be done. Endless chains also
    usually require time-consuming removal of the swingarm for
    replacement.

    Motorcycle drive chain contains two kinds of links. Roller links
    consist of two side plates, two rollers, and two bushings, all a
    slip fit over the drive pins. Pin links consist of two side plates
    and two drive pins, with the pins being a tight press fit into the
    side plates and staked in place for permanence. These links
    overlap, rollers on pins, to make the complete chain.

    Most chain is made in inch-based sizes, because the standard chain
    dimensions were established before much of the industrialized world
    had adopted the metric system. The basic chain size is given in
    terms of pitch, which is the on-centers distance between the
    rollers. The roller diameter is standardized at 5/8 of the chain's
    pitch dimension, so the common 5/8-pitch chain has a roller
    diameter of .391 inches. Unfortunately, no such uniformity exists
    in chain width, which varies a lot, as does sprocket thickness.
    Running a chain on sprockets which are too wide is usually a feat
    beyond even the most mechanically disinclined; unfortunately, it is
    also possible to run a chain on sprockets which are too narrow. The
    results of this are not good - the chain usually runs to one side
    of the sprocket, concentrating a majority of the load on one side
    of the chain, lowering its strength considerably and greatly
    increasing both load and wear.

    The loads on a chain are astounding. An average large-bore
    motorcycle in first gear can easily develop 1500 pounds of pull on
    the drive chain. The load-bearing area on the drive pins is about
    .075 square inches in circular contact, in reality, much less. The
    best-case loading for each pin is on the rough order of 20,000
    pounds per square inch! With this kind of load, chain wear becomes
    less of a mystery.

    The loads imposed by the engine are only part of the stresses
    inflicted on the chain. If you watch a motorcycle in motion, you
    will see that the slack side of the chain does not simply droop.
    Instead, it snakes and curves in a wavelike motion induced by its
    tendency to try to wrap itself around the sprocket. Stresses
    involved can be quite large. This threshing about adds to the
    relative motion between the pins and links and wears the chain out
    faster.

    Motorcyclists often refer to "chain stretch." This term is somewhat
    misleading. Chains do not actually stretch materially; any load
    large enough to appreciably stretch a chain would be as likely to
    snap it right in half. The stretch referred to is the growth in
    overall length of the chain due to wear in its many moving parts.

    The chain's pins pull very hard against the bushing walls and most
    of the wear occurs at those contact points. Loads carried by the
    bushing/roller contact surfaces are just as large but spread out
    over so much area that the pressure at any given point is much less
    than at the pins. In the normal course of events a chain's pins
    will be worn to their service limits long before the rollers are in
    any trouble. A chain is ready for replacement when stretch exceeds
    2 to 2.5 percent. On a 5/8-pitch chain, this figures out as about
    .0125-.0156" of slack per pin joint. Measuring each joint with a
    micrometer is not necessary. For example, a chain measuring 65
    inches has reached its service limit when its length has grown to
    66.3 to 66.63 inches.

    As the chain wears, the effective pitch between the links becomes
    greater. The chain's pitch becomes slightly longer that of its
    sprockets, causing the rollers to ride up on the teeth and apply
    pressure where the sprocket is narrow and weak. A properly-designed
    sprocket is designed to engage the chain's rollers gently, ease
    them down to the base of each tooth - where the load is taken - and
    then disengage smoothly and send the chain away. As the chain rides
    up on the teeth, sprocket wear increases dramatically.

    It would be nice if the sprocket makers would tell us how much a
    chain may stretch before it would no longer fit within the design
    limits of its the sprockets. Unfortunately, most sprockets come
    bulk packed, or, if we are lucky, they might be blister-packed to
    prevent them from being beaten up in shipment.

    Chain wear can be kept to a minimum by keeping it clean and
    properly lubricated.  Gasoline, kerosene/paraffin, and cleaning
    solvent are definite no-nos for cleaning chain. They can eat the O-
    ring seals and then hang around to contaminate the lubricant.  Wipe
    any dirt of sand off with a cloth, then apply your favorite lube.
    Specially-formulated chain lubes usually spray on like a thin oil
    to better penetrate the crevices and then congeal to better prevent
    being thrown off.

    Inexpensive non-O-ring sealed chains require much more frequent
    attention. On an unlubricated chain the friction between links can
    cause temperatures to rise to the point where the links can
    actually weld themselves together, putting a permanent kink in the
    chain.

    New chains have a breakin period, and that's when they have special
    need for proper lubrication. If their pins are well-oiled the
    loaded surfaces will be burnished smooth, leaving them in better
    condition to resist wear. Without adequate lubrication the surfaces
    will scuff and gall, greatly accelerating wear.

    The chain final drive has come to become the mark of the sporting
    machine. It is lightweight, mechanically efficient, inexpensive,
    and compact.  Chain technology is still developing, and it's likely
    we'll see chain drive used for a long time.

                          =====================

Q:  My engine has a magnetic drain plug.  Whenever I change the oil,
    it's always covered with tiny metal splinters and spooge.  Does
    this indicate problems in the engine?

A:  Probably not.  The magnet's purpose is to attract ferrous spooge.
    The gooey mess is tiny iron filings from your cams, cylinder walls,
    and other wearing surfaces.  It's basically the same sort of gick
    your oil filter traps.  Small splinters and pinhead-sized chunks
    are usually pieces of your transmission's engagement dogs.  It's
    normal to have *some* splinters even on carefully-ridden machines.
    A lot of them indicates missed shifts or worn shifter components.
    Pinhead-size or larger flakes usually mean the case hardening is
    coming off the gears.  That's a bad sign.

                          =====================

Q:  The front brakes on my bike make a buzzing noise.  I've looked all
    over and can't see any loose parts.  What is it?

A:  You probably have drilled or slotted rotors.  The holes often make
    a noise as they move past the pads.  Some bikes have floating rotors
    which can make intermittent noises.  In either case it's nothing to
    worry about.

Q:  Are drilled or slotted rotors more efficient than solid rotors?

A:  There are many different reasons rotors are drilled or slotted.
    Sometimes the rotors are drilled to lighten them, though your weight
    savings is probably negligible.  Honda claims the discontinuities
    help braking in the rain and provide an escape route for mud or
    rust.

    Fred Puhn's "Brake Handbook" says, "Some rotors have slots or holes
    machined into their contact surfaces.  These reduce hot-gas and
    dust-particle buildup between pad and rotor.  Although fade caused
    by gas buildup is less for a disc brake than for a drum brake, some
    fade still occurs.  This is more prevalent with large brake pads,
    because the hot gas has a harder time escaping than with small pads.
    Therefore, slots or holes have greater effect in racing, where pads
    are large and temperatures are very high."

    Newcomb & Spurr's "Braking of Road Vehicles", 1967, tells us the
    mass of the rotor is the primary factor for preventing brake fade.
    When the rotor mass has absorbed enough heat, the brake will fade.
    Vented rotors and ducting schemes will cool the rotor faster, but
    it takes time; in rapid repeated braking cycles vented rotors do
    little better than solid ones.

    Carroll Smith's "Prepare To Win", 1975, says "Lately you may have
    seen discs with tangential slots milled in the friction surfaces
    or holes drilled in a tangential pattern normal to the friction
    surface.  This is an effort to wipe the "fireband" or boundary
    layer off the disc before it reaches the point of contact with
    the pad and to provide the very hot particles of friction material
    worn off with some place to go other than the operating area."

(continued on next rock)