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Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Section - 8b.19 Tubular Tire Repair

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Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Previous Document: 8b.18 Tubular Fables
Next Document: 8b.20 Gluing Sew-up Tires
See reader questions & answers on this topic! - Help others by sharing your knowledge
Date:    Tue, 04 May 1999 11:07:38 PDT

Opening the Tire 
 
The tire casing must be opened to gain access to patch the tube.  To
do this, open the casing by peeling the base tape back and unstitching
the seam.  If this is a seamless tire, chuck it.  There are two types
of seams, zipper stitch (using one thread) and two thread stitch.  The
zipper stitch is identified by having only one thread.  It appears to
make a pattern of slanted arrows that point in the direction in which
it can be 'unzipped'.

Never open more tire than is necessary to pull the tube out of the
casing.  Remember, the tube is elastic and can be pulled a long way
from a three cm long opening.  Even if there are two punctures not too
far apart, the tube can be pulled out of a nearby opening.  However,
to insert a boot requires an opening of about 6 to 10 cm at the
location of the cut or rupture, about the length of the boot (at least
10cm) and a couple of cm more.
 
Base Tape 
 
Never cut the base tape because it cannot be butt joined.  Always pull
it to one side or separate it where it is overlapped.  Do not cut the
stitching, because it takes more time to pull out the cut thread than
to pull it out in one piece.  When working on the stem, only unstitch
on one side of the stem, preferably the side where machine finished.
Use latex to glue down loose threads on a sidewall cut.  Paint the
exposed casing zone that is to be covered by the base tape and the
tape with latex emulsion, allow to partially dry and put the tape in
place.  Put the tire on a rim and inflate hard.
 
Seam Ripper and Triangular Needle

A convenient tool, available in the sewing department at most
department and sewing specialty stores is a seam ripper.  This and the
triangular sewing needle from a Velox patch kit are two highly useful
tools for tubular repair, scissors and razor blades being common
household items.

Zipper Stitch 
 
Cut the thread at some convenient place at the upstream end of the
intended opening and with a blunt awl, like a knitting needle, pull
out several stitches in the direction the stitch pattern points.  When
enough thread is free to pull on, the stitching can be opened like a
zipper.  When enough seam is open, thread the loose end through the
last loop and pull tight, to lock the zipper.  Don't cut off the free
end because it is often good enough to re-sew the seam.

Two Thread Stitch 
 
One of the threads makes a zig zag as it locks the other thread where
it penetrates the tire casing.  Cut both threads near the middle of
the opening and, with a blunt awl like a knitting needle, pull out
only the locking thread in both directions, stitch at a time.  The
locking thread is the one that is easier to pull out.  Remove as many
stitches as the opening requires.  The other thread pulls out like a
zipper.  Tie a square knot with the loose ends at both ends of the
opening and cut off the rest.

Patching 
 
Patch butyl (black) tubes using patches from a bicycle patch kit. 
 
To patch a latex tube, make patches from an old latex tube that are
fully rounded and just large enough to cover the hole plus five mm.
For instance, a thorn hole takes a 10 mm diameter patch.  Use Pastali
rim glue (tire patch glue also works but not as well) wiped thinly
onto the patch with your finger.  Place the patch on the tube
immediately and press flat.  Latex will pass the volatile solvent
allowing the glue to cure rapidly with good adhesion to the tube.
 
Casing Repair 
 
Repairing tubular tires requires latex emulsion.  You can get it from
carpet layers, who usually have it in bulk.  You must have a container
and beg for a serving.  If you are repairing a tubular you probably
ride them, and therefore, will have dead ones lying around.  The best
tubulars generally furnish the best repair material.
 
Most cuts of more than a few cords, like a glass cut, require a
structural boot.  With thin latex tubes, uncovered casing cuts will
soon nibble through the tube and cause another flat.  For boot
material, pull the tread off a silk sprint tire, unstitch it and cut
off the bead at the edge of the fold.  Now you have a long ribbon of
fine boot material.  Cut off a 10cm long piece and trim it to a width
that just fits inside the casing of the tire to be booted from inside
edge of the bead (the folded part) to the other edge.
 
The boot must be trimmed using a razor blade to a thin feathered edge
so that the tube is not exposed to a step at the boot's edge,
otherwise this will wear pinholes in a thin latex tube.  Apply latex
to the cleaner side of the boot and the area inside the tire,
preferably so the boot cords are 90 degrees from the facing tire
cords.  

Insert the boot and press it into place, preferably in the natural
curve of the tire.  This makes the the boot the principal structural
support when the tire is again inflated, after the boot cures.  If the
casing is flat when the boot is glued, it will stretch the casing more
than the boot upon inflation.  After the boot dries, and this goes
rapidly, sew the tire.

Valve Stem Replacement

This depends on the type of tube.  Latex tubes and some of the others
have a screwed in stem that has a mushroomed end on the inside and a
washer and nut on the outside.  These are easily replaced from another
tire whose tube is shot.  Open the old ruined tire at the stem, loosen
the nut, lift the washer and pull out the stem.

Open the tire to be repaired on one side of the stem, preferably the
side where sewing ended, the messier side, and loosen the base nut,
lift the washer, wet the stem at the tube opening with saliva and
twist it until it turns freely.  Pull it out carefully and insert the
replacement stem after wetting its mushroom with saliva.  Tire
stores have a soapy mixture called "Ru-glide" or the like to do the
wetting but it cost a lot more than spit and doesn't work any better.
 
Tube Replacement 
 
To replace the entire tube, open the tire on one side of the stem, the
side that seems to be easier to re-sew after the repair.  Open about
eight to ten cm the usual way, so that the old tube can be pulled out
by the stem.  Cut the tube and attach a strong cord to the loose end
of the tube to be pulled through the casing by the old tube as you
pull it out.
 
Cut the "new" latex tube about 8-10 cm away from the stem, tie the
cord onto the loose end and pull it gently into the casing.  Dumping
some talc into the casing and putting talc onto the tube helps get the
tube into place.  With the tube in place, pull enough of it out by
stretching it, to splice the ends together.
 
Splicing the Tube 
 
This procedure works only with latex tubes.  Overlap the tube ends so
the free end goes about one cm inside the end with the stem.  With the
tube overlapped, use a toothpick to wipe Pastali rim cement into the
interface.  The reason this MUST be done in place is that the solvent
will curl the rubber into an unmanageable mess if you try this in free
space.  Carefully glue the entire circumference and press the joint
together by pressing the tube flat in opposing directions.  Wait a
minute and then gently inflate to check the results.  More glue can be
inserted if necessary if you do not wait too long.
 
Sewing the Tire 
 
Sewing machines make holes through the bead that are straight across
at a regular stitch interval.  For best results, use the original
stitch holes when re-sewing.  Use a strong thread (one that you cannot
tear by hand) and a (triangular) needle from a Velox tubular patch kit
(yes I know they are scarce).  Make the first stitch about one stitch
behind the last remaining machine stitch and tie it off with a noose
knot.
 
With the beads of the tire pressed against each other so that the old
holes are exactly aligned, sew using a loop stitch pulling each stitch
tight, going forward two holes then back one, forward two, back one,
until the seam is closed.  This is a balanced stitch that uses one
thread and can stretch longitudinally.
 
Gluing Tire to Rim

For road tires, that are intended to be manually mounted and replaced
on the road, tires with a rubberized base tape are preferred because
these are easily and securely mounted by applying a coating of glue to
the rim, allowing it to harden and mounting the tire to be inflated
hard so that it will sink in and set.

Because road tires are intended to be changed on the road, they use a
glue that does not completely harden and allows reuse for mounting a
spare.

Track tires, in contrast can be mounted using hardening glue such as
shellac or bicycle tire track glue.  This glue is best suited for base
tapes that are "dry" cloth.  The tire is mounted either with a light
coating of track glue on the base tape or un-glued onto a good base of
track glue whose last coat is still soft on the rim, into which the
tire will set when inflated upon mounting.  Hard glue prevents rolling
resistance otherwise generated by the gummy road glue.  Track glue is
primarily useful for record attempts where every effort is needed.

Mounting a Tubular

The most effective and fastest way to mount a tubular is to place the
rim upright on the ground, stem hole up; insert the valve stem of the
tire and with both hands stretch the tire with downward force to
either side, working the hands downward to the bottom of the rim
without allowing the tire to slacken.  Try this before applying rim
glue on a dry rim and inflate the tire hard so that afterward,
mounting is easier on the glued rim.

Note that inflation pressure causes the tire to constrict until the
cord plies are at about 35 degrees.  This effect helps retain the tire
on the rim in use.  Therefore, do not inflate a tire to mount it.
Tubulars should generally not be inflated off a rim because this
deforms the tire and base tape adversely, possibly shearing the
inter-ply adhesion and loosening the base tape and stitching.

Now that you know everything there is to know about this, get some 
practice.  It works, I did it for years. 

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Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Previous Document: 8b.18 Tubular Fables
Next Document: 8b.20 Gluing Sew-up Tires

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