I suppose the key point to adjusting this system, and the twin-ear
system, is to make sure that it doesn't shred the rolls in rewind.

As Dan Wilson said, the single-ear system has a sprung pneumatic that
locks the tracking into the centre position on reroll.  This pneumatic
is pulled down during play (it's connected to the stack supply), and
springs up on reroll.  On some instruments it appears to be a
retro-fit, so there may be single-ear systems without it.  If you have
a single-ear tracking system which cannot be locked during reroll,
consider adding the lock.

The more familiar double-ear tracking system uses a pneumatic locking
mechanism to hold the system centred during reroll -- which is
seriously prone to mistubing during rebuilding.  This experience is
from UK machines; I don't know whether US machines are similar.

The pneumatic locking of the twin-ear tracking system during reroll is
achieved by powering the tracking pneumatics but blocking the inputs
from the tracking ears.  This prevents the pneumatics from being
operated when the tracking ears are triggered.  To achieve this, there
are two suction supplies to the tracking valve box: one is powered
during both play and rewind (connected from foot pedal box to the
pneumatics), and the other (connected from stack supply to the valve
cutoffs) is switched off during rewind.

Unfortunately, there's a 50-50 chance these two will get reversed
during rebuilding, or even minor maintenance work.  If that happens,
the tracking system will not be powered during rewind, and will shift
to one side under the influence of gravity and the sprung roll chuck.

Result: top spool way out of alignment with bottom, so one edge of the
roll gets chewed up.  That's the reason so many rolls with perfectly
good paper have one shattered edge (normally the left).  Once such
rolls are played on a properly set-up machine, they behave perfectly
and don't suffer any more damage.

The fix to this problem is simple: pull off the two suction supply
tubes to the tracking system and reverse them!

Obviously, for the reroll lock to be effective, the top and bottom
spools must be aligned perfectly with each other when the tracking
system is centred.  The spools are normally adjusted with simple set
screws or locked collars.  This is easy stuff for even the
non-technical owner to check, and it makes the world of difference.

Julian Dyer