Race Preparation - General Maintenance

How to check the diffs -
Always refer to the car instruction manual for detailed guidance.

1. With the motor pinion and drive train engaged, turn one wheel at the rear of the car several times (backwards and forwards). The other wheel should move in the opposite direction and the action should be smooth.
   If the movement is rough, or 'grates', the diff may require a service (see below).
2. Repeat for the front diff.
3. Hold one rear wheel and the spur gear so that neither can move. Attempt to turn the other rear wheel - this can be a difficult operation without help. If the wheel will turn, the diff is loose - refer to the car manual.
4. Repeat for the front diff.

How to test the car for rolling resistance

1. Remove the motor pinion - or move the motor - to disconnect the motor from the drive train.
2. Secure the car on a platform, with the wheels raised, and spin the rear wheels.
3. All four wheels should spin easily and continue to spin for a few seconds.
4. Alternatively, push the car along the ground (smooth surface).
5. If the car appears sluggish, check the drive belt - is it tight?
6. If the belt is ok (or the car is shaft-driven), check each wheel independently - does any wheel rub against the chassis?
7. To check the wheel bearing, disconnect the wheel hub from the top wishbone and withdraw the drive shaft from the diff. The shaft can then be rotated manually within its bearings. It is ok for the bearings to 'rumble' provided they turn easily - and have been oiled recently.
8. Check, clean and lubricate all bearings if necessary.
9. Inspect the inside of the body shell around the wheel arches - is there evidence of the wheels rubbing?
   Enlarge the wheel arches if necessary.
10. After re-assembly, spin the wheels again to check for improvement.

Chassis/Suspension movement

1. Remove the wheels and disconnect the shock absorbers.
2. Lift each corner assembly and watch it drop. It should fall easily under its own weight.
3. Look at each pair of suspension assemblies (front and back). Are they resting at the same angle?. If not, look for obstructions (including uneven droop screws). Adjust as necessary.
4. Disconnect the wheel hub from the top wishbone and repeat the test for top and bottom wishbones separately. Each should move freely. If not, dismantle and check for obstructions. Sometimes it is necessary to remove a small layer of plastic from the moving faces - a very delicate operation.
5. Repeat for each suspension assembly.
6. All suspension parts should now move freely and evenly.
7. Close each shock absorber to check for freedom of movement - make sure the piston rods are not bent!
8. Measure the length of each shock absorber at full extension and 'rest'. Full extension length should be identical - adjust as necessary. 'Rest' length can vary slightly if close to the fully closed length. If 'rest' length is too varied - or too close to full extension length, a service is required.

How to check and service the bearings

1. Refer to the car instruction manual for the location of all bearings (usually each wheel hub, diff, layshaft, and belt tensioner).
2. Remove bearings - one section at a time or all together - be careful to retain and note the positions of any spacers and retaining clips.
3. Place each bearing on a suitable shaft (long-nosed pliers?) and spin. If it spins freely for several seconds, apply one drop of motor oil to each side panel and 'work' the oil in. Spin the bearing. The oil will act as additional resistance, so the bearing will not spin so long - but it should be smooth.
4. If the movement is restricted, immerse bearing in a jar of clean motor cleaning fluid for several hours, agitating frequently. Test and apply oil once it runs freely
5. Alternatively, remove the side panels from any bearings which are stiff and spray with motor cleaner until free movement is achieved. This is a difficult operation for some bearings.
6. Discard any bearings which cannot be cleaned to 'free-running' status and replace with new bearings. New bearings should have the greased 'washed' out by long term immersion in motor fluid if high competition speeds are required.
7. Wipe surplus oil from the bearings and re-assemble.

How to check and service the shock absorbers

1. Remove each shock absorber from the car.
2. Remove all springs and spacers.
3. Hold a shock absorber close to your ear and slowly operate it (close, then open). The movement should be quiet.
4. A 'gurgling' sound indicates air mixed with the oil - which impairs efficency.
5. Push the shaft into the barrel and release. If the shaft recoils more than a very short distance, the shock absorber has too much air mixed with the oil, and the oil must be changed.
6. Refer to the car instruction manual for the method of assembly/dis-assembly.
7. Empty the shock barrel and wipe it clean/dry.
8. Refill and reassemble carefully in accordance with the instruction manual.
9. Re-test and repeat if necessary.
10. Repeat for all shock absorbers and test measured lengths (fully extended and 'rest'). Adjust so all shocks are exactly equal.

How to skim a motor
A motor lathe is a delicate and expensive piece of equipment. Oddly, the manufacturers don't offer much in the way of operator guidance.

If the motor commutator is cleaned frequently, the motor will operate successfully for a long time. Eventually, the path of the brushes will wear a significant 'dip' in the surface.
Regular 'light skims' will keep the motor in top condition - provided the brushes are changed at the same time. Costs are not excessive, but on a limited budget, it may be preferable to sacrifice performance, and skim the motor less frequently.

1. Extract the armature from the motor. Remove and carefully retain spacers and washers from each end of the shaft.
2. Place the drive band around the armature and fit it into the lathe. Adjust or add packing washers to eliminate any end-play.
3. Spin the armature by hand to ensure correctly positioned then connect the drive band to the pulley.
4. Ensure the cutting tool is away from the armature before switching on the drive motor.
5. Adjust the cutting tool so that it just touches the armature.
6. Carefully wind the travel handle so that the cutting tool passes along the armature slowly, and back to the start point. A fresh surface will be revealed.
7. Stop the motor and check the armature.
8. Continue the process until the armature has a uniform, fresh, shiny surface. Clean the cutting tool with a brush or cloth after each 'pass'.
9. Remove the armature from the lathe and wipe the shaft ends. Ensure that the armature slots are clear (a 'biro' run along each slot will soften the edge).
10. Replace the spacers and washers. Add a drop of oil to each end of the shaft.
11. Reassemble the motor
12. Renew the brushes
13. Run the motor for a few minutes at low speed.