you are fortunate enough to own a Hammond organ, then you are even more
fortunate if it is connected to a Leslie cabinet. Up to fairly recently,
the service requirements of the organ have seldom extended to more than
its yearly lubrication and an occasional new set of valves. The Leslie,
however, usually has to work much harder for its living than the organ does;
the rotors are continually speeding up and slowing down, the motors run
at a surprisingly high temperature, the amplifiers produce appreciable heat,
and the speakers are often subjected to high power levels. The service requirements
to keep a Leslie in good repair are wide ranging and many jobs reach grade
4 and 5. The simpler routine jobs which are listed below are well worth
doing, and lubricating the motors is absolutely vital. This job would otherwise
be judged too difficult for most organ owners, but a detailed guide is given
below to help you through the work. However, if you have a service engineer,
this is a job for him.
Rotor, lubrication. Grade 1
The twin horns of the treble rotor have a large cylindrical precision
bearing that requires little oil. Since the oiling hole is both conspicuous
and accessible, this bearing is often over-lubricated, resulting in
oil seeping down into the treble driver below. A few drops per year
is sufficient. For the sake of simplicity, use the same oil as for lubricating
the motors - good car engine oil - although lighter oil is somewhat
Rotor, drive belt replacement. Grade 1.
If the woven cotton drive belt has started to fray, or has rolled back
to reveal the inner layers, it must be replaced. This is a very simple
job requiring no dismantling or adjustment. Put a single drop of oil
onto the centre of the tensioning wheel while you are 'in the area'.
Rotor, bearing replacement. Grade 3.
For many years, cleaning and re-greasing the two bass rotor bearings
has been enough to keep rumble at bay. This is no longer a worthwhile
solution if rumble is a problem, and the bearings should be completely
replaced. A ball bearing specialist will have replacements, if you show
the old ones.
Rotor, drive belt replacement. Grade 2.
The original belt is very robust, and if run at the correct tension
seldom needs replacement. However, if it has been overtightened, the
internal stranding will eventually start rupturing, and a short length
of the belt will appear thinner than the rest. This waisted section
will cause a periodic bumping as it passes over the motor's drive pulley,
and the belt must be replaced. The bass speaker must be removed, whereafter
the replacement of the belt is simple. Thereafter, you must readjust
the belt tension, which is tricky. Loosen the wingnut on the bass motor's
nearmost fixing bolt (on the underside of the mounting shelf) and slide
the motor sidewards. To arrive at just the right tension, you must sharpen
your wits, your eyes and your ears! If the belt is too slack, it will
slip on the motor pulley, resulting in an acceleration time from slow
to fast speed of over 10 sec. Watch the wheel on the motor with the
black rubber ring on its perimeter, noting carefully how it speeds up
when someone else switches the organ from slow to fast ('chorale' to
'tremolo', in Leslie-speak). When slippage occurs, you will hear a swishing
sound from the belt where it passes over the motor pulley. At the correct
belt tension, the pulley/belt/rotor will all accelerate in step with
each other for about two sec. Then, the motor's torque will surge forwards,
it will accelerate quickly up to full speed leaving the belt and rotor
behind, and slippage occurs (listen for the swish!) It will then take
a further 6 sec. for the belt and rotor to catch up, and the swishing
sound fades away. Loosen the wingnut that you can see on the under side
of the mounting board, and swing the motor to the left in order to tension
Move the motor sidewards to tension the belt.
Tighten the wingnut loosely to fix the motor's position. The cotton
belt will stretch successively over the period of a week, during which
time you must readjust the tension several times - like tuning new strings
on a guitar. Then you can tighten the wingnut properly.
motor adjustment. Grade 2.
All Leslie owners must learn how to do this themselves, since it
must be carried out periodically to compensate for the wear to the 'O'
ring caused by the slow motor's axle. The job description is found in
the last stage of 'Lubricating the Motors'.
the Motors. Grade 3. Most Leslie cabinets have motors which
are seriously under-lubricated. Many have received almost no oil since
manufacture, in which case the motors will be very worn. If your own Leslie
is to survive, oiling the motors properly is vital. Renovating worn motors
is an expensive grade 5 job, and is sometimes impossible. To do this job,
move the Leslie to somewhere with plenty of space, good lighting and clean
working surfaces. Work carefully, slowly and methodically, whilst making
a mental or written note of the order of dismantling/orientation of each
part. Before you start, collect the following items;
a good tool kit
1/4" nut driver
5/16" nut driver and spanner, although 8mm usually works
3/32" allen key. This tool is vital; don't start without it.
new 'O' ring for each motor unit, unless the existing ones are good
(i.e. a flat surface has not been worn on the 'O' ring's perimeter).
Their internal diameter is 63-64mm, and thickness is 5.3mm. Soft 70
shore nitril is a suitable material. If you are unable to get these
from a supplier of Leslie parts, they are available from the suppliers
of spare parts for hydraulic equipment, although these sometimes have
a coefficient of friction which is too low.
engine oil in an oiling can.
There is a two-speed motor assembly for each of the Leslie's rotors;
typically one in the lower part of the cabinet for the bass rotor, and
another at the top for the treble rotor. Both motor assemblies must
be removed from the cabinet. Extracting the treble motor assembly is
awkward; lift it up into the rotor compartment, whereafter a haphazard
sequence of twisting and turning will eventually get it out. Studying
the motor assemblies, you will observe that each consists of a small
open frame motor (for the slow speed) attached to a larger, black, enclosed
motor (for the fast speed). The slow motor must be separated from the
fast motor. Remove four 1/4" hex head screws that fix the slow
motor's aluminium mounting plate to a large black 'U' bracket. Now turn
your attention to the wheel with the black 'O' ring, which is attached
to the fast motor's axle., making a very careful note of how far from
the end of the axle. it is fixed; upon re-assembly you must return it
to this position exactly. The wheel may then be removed by slackening
its allen screw with your 3/32" Allen key, and withdrawing it from
the fast motor's axle. The 'U' bracket is then removed by unscrewing
the three screws which attach it to the fast motor.
Oiling the fast motor.
The motor's two black end plates have a circle of access holes around
the axle., through which oil can be applied to a felt ring on the inside
of the plate. Apply about 10 drops of oil to each felt, doing so very
slowly so that gravity draws each drop down to the felt.
the motors with good car engine oil.
Oiling the slow motor.
The axle. is supported at each end by an aluminium casting and bearing.
On one of these castings, a small oiling hole is clearly visible close
to the axle. Apply about 6 drops of oil here, giving each drop time
to sink in. The bearing in the other casting requires identical treatment,
but is obscured by the aluminium mounting plate. It is therefore easier
to apply oil to the inside of the casting instead, in the gap around
the inaccessible end of the slow motor.
Concealed behind the oval plate on the inside of the casting, there
is a round felt washer similar to those on the fast motor. This will
absorb the oil as it runs in. The part of the slow motor's axle. that
engages the 'O' ring must be wiped completely clean of oil, as this
would cause slippage on the 'O' ring.
Remove the old 'O' ring, and replace it with a new one, taking care
to correct the twist that occurs as it is put on. A faint moulding-line
is usually visible around the exact perimeter of the 'O' ring, (strong
reading spectacles help to identify this line) which acts as a guide
when straightening the 'O' ring. Never reuse a worn 'O' ring by turning
it inside out!
Re-attatch the 'U' bracket; you will find there is only one way that
the three screw holes line up. Tighten the screws fairly hard. Then
place the wheel on the axle. and fix it exactly at its old location,
ensuring that the Allen screw is perpendicular to the flat on the axle.
by 'jiggling' the wheel continually as you tighten the screw with the
Allen key. Re-attatch the slow motor with the four 1/4" screws,
which should not be tightened too hard, to avoid stripping the threads
in the mounting plate.
Slow motor adjustment.
This procedure must be carried out by all Leslie owners, to periodically
compensate for the slow motor wearing a flat area on the perimeter of
the 'O' ring. It must also be done now, after replacing the 'O' ring.
You will find it useful to understand how the whole system works...
When the Leslie control on the organ is at tremolo (fast), the circuitry
applies electric power to the large, fast motor only. This motor turn
rapidly, spinning the rotor to which it is attached When the Leslie
control is moved to chorale (slow), the power is transferred from the
fast motor to the slow motor. Its axle rotates and jumps towards the
'O' ring and engages upon it. The wheel turns slowly since its diameter
is much larger than the slow motor's axle., and in turn the rotor rotates
slowly. Here, the fast motor acts passively as a step down gear box.
If the rotor fails to rotate at slow speed, the fault is invariably
that the the pressure of the axle. on the 'O' ring is too weak to draw
it round, and slippage is occurring. To increase this pressure, the
motor is angled inwards slightly by an adjustment screw. You will observe
that the slow motor is attached to the mounting plate by two long screws
either side of the axle., as well as a third screw which passes straight
through the motor's black laminations. By moving the nuts on either
side of the laminations up or down, the motor can be tipped to increase
or decrease the axle. pressure on the 'O' ring. This pressure must be
sufficient to create enough friction to draw the 'O' ring round. Slippage
can also be caused by oil on the 'O' ring and axle., which must be kept
absolutely clean. If the nuts are adjusted too far, the axle pressure
will be excessive, causing unnecessary wear on the bearings, as well
as making the axle. reluctant to return to it neutral position when
the speed is change back to fast.
the pressure angle of the slow motor.
The nuts are finally tightened firmly against one another when just the
right pressure has been found, for which two 5/16" (or 8mm) spanners
are required. On most Leslies, the bass motor assembly is readily accessible
and this adjustment can be done on the spot. The treble motor, being enclosed
by its little wooden box, is difficult. At first, it would be easier if
you have help from another person to move the Leslie control back and
forth, and someone else to hold the motor outside the cabinet, while you
become accustomed to performing the adjustment.