If 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.


Treble 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 preferable.


Treble 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'.


Bass 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.


Bass 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 the belt.

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.


Slow 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'.


Lubricating 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
  • a 1/4" nut driver
  • a 5/16" nut driver and spanner, although 8mm usually works
  • a 3/32" allen key. This tool is vital; don't start without it.
  • a 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.
  • car 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.

Lubricate 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 axle.

Oiling 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.

Adjusting 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.