In response to Mark Poole's post [160704 MMDigest, from the image
he supplied, the current position of the drive dog should not stop
the disc nor make a 'popping' sound.  From his description, without
inspection of the machine, it's more indicative of bent projections
on the disc, which brings me to cleaning.

A full descriptive process for care of the machine and discs is laid
out in Graham Webb's book, "The Disc Musical Box Handbook" (Faber),
a copy of which is a must for anyone uninitiated or having a mechanical
interest in their box.

I would suggest that the discs are looked at intimately; turn the disc
upside down, index finger placed in centre hole and rest supported by
thumb and remaining fingers.  With a minimum of practice a disc can be
read for bent projections, scanning with the eye from the periphery
to the centre (think of lines of longitude) and discrepancies will be
revealed and can be trimmed accordingly with a pair of fine long-nose
pliers.

Any light surface rust can be removed with a soft brass brush used for
suede shoes, adopting a radial motion.  Slow unhurried strokes, keeping
brush as near horizontal will prevent a projection rash on the knuckles.
Ouch!

I would not recommend the use of any chemical cleaning compounds --
apart from being environmentally unfriendly and probable carcinogens,
they will undoubtedly lift the applied factory text.  A little
washing-up liquid is more than sufficient to help them on their way.

On the top side, for aesthetic reasons, they can be cleaned again with
washing-up liquid, and using a wad of wet 0000 gauge steel wool, work
in a radial pattern, taking care in areas of text, and ensuring that
the areas around the drive holes are free from rust and little creases
on both sides.  Rinse and dry immediately.  At this point, resist the
application of any spray lubricants, for any residue will probably work
its way through your star wheel gantry and foul up your dampers.

Place the now clean disc face down and spray a mere dusting of a good
household furniture polish that contains beeswax; this can be then
polished off with a large soft, _natural_ hair/bristle paint brush,
of at least 125 or 150 mm.  This action seals the pores on the metal,
and helps towards a smooth mating with the starwheels.  A dusting on
a cloth can be wiped over the top surface, taking care to leave no
residue, and making sure the peripheral area, especially at the rear
has had a good polish.  Your disc is now ready to play without any
extraneous noises.

If the drive dog is still giving cause for concern, yes its height can
be adjusted, but I would not immediately advise this.  Remember a large
upright is a heavy instrument, and from your image it appears to be an
early large motor style 54 Mikado.  Getting on +\-120 years it's been
moved a fair few times and the easiest way to avoid a hernia is to
remove the bedplate and motor in the process.

Your box, in all probability, would not have been fitted with the
L-shaped locating plates that ensures an accurate fit on replacement
of the bed plate; being heavy it's easier for some to just rest the
bed on the motor cover locating rail.

Take a couple of small shims of between 0.5 to 0.75 mm to rest the bed
on while re-fastening.  I always stand the retaining screws upright
prior to re-assembly and apply a small drip of light oil, with a host
of good reasons -- namely, the screws should go almost all the way home
at this point without the need of a screwdriver, and this allows you to
further ease the bedplate into optimum position.  Gently nip the screws
tight in a diagonal fashion, and try not to turn more than 1/8-turn
after hitting resistance.  Hopefully this two-minute tweak should
rectify this minor malady.

I always try to keep a spare copy of Webb's book; it's a soothing balm
and of great emotional comfort for the seemingly incurable Polyphonitis
disease.  ;))

Mark Singleton
Lancashire, UK