John Farmer asks about lubricating old motors [090317 MMDigest].  Old
motors usually used sintered bronze bushes.  These were baked and as
a result the bronze became porous.  Before use, bushes were soaked in
oil for a couple of weeks to allow lubricating oil to fill the voids.
They were known also as self-lubricating bushes.

The nice thing about old mechanical bits is that the Imperial sizes
are generally still available new from our friends in USA because they
insist on using Imperial dimensions based on 1/2^n size increments.
I usually never have any difficulty obtaining new bushes for the most
unusual and old-fashioned stuff.  I have renewed bushes in an old 1925
Buick starter-generator.

The actual mechanical layout of John's motor is most likely to include
some kind of oil wick which can be periodically doused with oil to
maintain the bush in an oiled state.  Bushes were common before ball
bearings became so cheap.

The motor is said to be a 40 Hz machine.  The motor design will be such
that there is enough turns on the motor windings to prevent magnetic
saturation of the iron circuit at 40 Hz.  Given the basic design of the
motor, running it on a higher mains frequency will result in a reduction
of the motor magnetising current (this is good) and an increase in the
rotational speed.

The rpm of a motor is governed by the number of poles (2, 4, 6, 8,
etc.).  Motors for common appliance work are 4 or 6 pole.  The speed is
given by N = 120*f/P where f is the mains frequency, Hz.

So, a 4-pole motor running on 40 Hz mains frequency runs at 120*40/4 =
1200 RPM.  If this motor now runs on 50 Hz the speed is 120*50/4 = 1500
RPM.  In actual fact a squirrel cage motor will normally run at a speed
of about 4% less than the calculated [synchronous] speed.  To run the
nickelodeon at about the original speed, the diameter of the motor pulley
can be reduced to 40/50ths of the original size.  Hope this all helps.

Paul Rumpf
Melbourne, Australia