Below are my thoughts on electric model locomotive maintenance (including powered multiple units) which are listed below. They apply mainly to items made from the late 1970s onwards that are ready-to-run and produced in 'OO' gauge:
Do not dismantle the locomotive unless you have to because it has stopped working.
"If it ain't broke - don't fix it". If it is still under the manufacturer's warranty, it is probably best to return it the shop where it was purchased or to the manufacturer, depending on the terms of the warranty. If the locomotive is old or second-hand, make sure any obvious fluff or loose metallic objects are removed before cleaning and oiling. Staples, iron filings and track pins are often attracted to the magnets on motors and can cause electrical shorting and other damage. Make sure that any articulated bogies move freely or they may cause derailments. For example, on the Hornby class 110 diesel multiple unit, the bogies are sometimes too tightly fitted to the chassis and this can cause derailments. The bogies can be unclipped by hand and the surface on the end of the bogies that rubs on the curved part of the chassis can be bent or filed back a little to improve running. Do not try this unless you have problems with the running of the item and are sure you know what you are doing.
Clean wheels regularly to avoid a build up of dirt causing excess electrical arcing and potential damage to the wheels and track.
Unpowered wheels and some powered ones can be gently turned by hand to expose more surface for cleaning. The powered wheels on some locomotives will need electrical power to turn them. This can be achieved by driving the locomotive short distances along the track or by applying power from a fly-lead to the wheels with electrical pick-up. Many modern locomotives have fragile detail parts on the bodies and chassis, so great care should be taken in handling them. A padded cradle can be made or purchased to safely invert locomotives for wheel cleaning. Wheels can be cleaned with a soft, non-abrasive cloth and a solvent such as methylated spirits (meths). Do not use metal polish as this will gradually wear away the thin chromium coating on many model locomotive wheels. Thick deposits of rubber from track cleaners and locomotive rubber traction tyres can be gently loosened with a wooden paint brush handle or small flat-bladed screwdriver, taking great care not to scratch any chrome coating. Damage to the chrome coating present on some wheels will cause dirt to build up more quickly. Some locomotive wheels, such as those made by Lima from the 1980s onwards are supplied with chemically blackened brass wheels for a more realistic effect, but this coating probably does not help electrical conductivity and tends to hide any dirt. If desired, this coating can be gently burnished from the wheel treads, leaving the shiny brass underneath, using an abrasive Peco track cleaner or 'rubber' - available from model shops. This must not be used on wheels with a metal plating as it will cause damage to the plating. A glass fibre burnishing 'pen' (also available from model shops) can also be used for wheel cleaning, but again I would not recommend this for metal-plated wheels. There is also a danger that the loosened glass fibre particles could cause skin or breathing irritation, so these pens should be used with great care. Please note that many current models use plated wheels that have also been chemically blackened, so if in any doubt, always use a cloth and solvent for cleaning and never use anything in any way abrasive.
Cleaning the track is just as important as cleaning the wheels, for the same reason.
Take care of both sharp rail edges and fragile lineside structures such as signals when cleaning the track. Point blades can be broken by rough cleaning. Coated steel track (silvery-grey in colour) should be cleaned with a non-abrasive cloth and a solvent, in a similar manner to the suggestion for wheel cleaning. Nickel silver track (slightly yellowy in colour, currently more common than steel) can be cleaned in the same way and additionally, more serious build-ups of dirt can be cleaned with an abrasive Peco track rubber. If a Peco track rubber has been used, the track should then be further cleaned with a cloth and solvent to remove the small particles of rubbery material that will have been deposited by the rubber. Failure to remove these particles will in itself make track and wheels dirtier. All track should be accessible for cleaning and maintenance, so remember this when you are planning a layout.
Metal moving parts should be lubricated.
Always use oil very sparingly and use very thin sewing machine or 3-in-1 oil, not engine oil. Oil can be applied from a hypodermic syringe or very carefully from a small oil can with a hypodermic needle on top or via a pin point. If oil gets onto electrically conductive surfaces such as the wheels or the copper commutator of the motor it could severely affect the performance of the locomotive and may cause a dirt build-up, smoking and damage. Most locomotives will only need the tiniest dot of oil possible on the bearings of the motor armature to stop them squeaking or 'screaming'. Some locomotives seem not to need oiling at all. Take care as some oils may damage plastic parts.
After heavy or prolonged usage, the motor may need attention.
This is more likely on elderly, second-hand locomotives. Do not interfere with the motor unless the above cleaning and lubricating has not improved matters and you are confident in the way that the locomotive works and is assembled. Do not attempt to open sealed motors. Inspect the brushes, usually carbon, that rub on the copper commutator of the motor armature. Take care as they will be spring-loaded and may fly across the room unless removed carefully. The faces of the brushes and commutator should be flat and free from dirt and oil. Make sure that the brush springs make good electrical contact with their housings and that the brushes are being gently pressed onto the commutator by the springs. Replace damaged brushes and/or springs. The gaps between the sectors of the commutator can be cleaned with a pin and the copper face of the commutator can be cleaned with a paint brush or cotton bud and solvent. In my experience, some very old Hornby ring-field motors (pre-1980s?) with phosphor-bronze bearings can loosen their bearings, causing the motor windings to rub on the casing on the output end (with the spur gear) and eventually break, potentially ruining the motor. The windings can sometimes be very carefully soldered back together, but this is a very fiddly job. A spacing washer can be inserted onto the motor armature axle between the casing and the windings if the bearing is loose. To do this, the spur gear will first have to be removed to release the armature and I'm afraid gentle tapping with a hammer on the end of the armature shaft with the other end of the armature free seems to be a good way to do this, although you may be able to use a worm gear puller. It might also be worth trying to super-glue the loose bearing in place. Re-assemble in reverse order, taking care that the gears mesh properly wherever the motor armature sits in its bearings (there should be a little 'play' in and out of the bearings).
The wheel back-to-back measurement should be correct...
On standard 16.5mm gauge 'OO' Peco track, as used by the Solihull Model Railway Circle, there should be precisely 14.5mm between the insides of the wheels. Model locomotives built before the late 1970s, such as Hornby-Dublo ones will probably not work properly on this track and are likely to de-rail on points (turnouts). Steam locomotive wheels cannot usually be adjusted, but diesel and electric locomotives and multiple units can usually have this back-to-back measurement adjusted if absolutely necessary. This will probably only be required if the locomotive suffers continual derailments on track where other locos run perfectly. Do not try to adjust the wheels if the back-to-back measurement is correct as there is probably another problem such as a loose chassis part fouling the track. Where the wheels can be adjusted, such as on many Hornby and Lima 'modern image' locos from the 1980s and 1990s, they can usually be gently pressed in by hand or prised out with a small screwdriver until the back-to-back measurement is correct. Make sure that the gears on driven axles still mesh correctly, possibly with the aid of spacing washers on the axles. Make sure that the wheel remains square on the axle or the locomotive will wobble and not run properly. Take extra care with Hornby powered axles as they can easily bend out of 'true'. Do not attempt this unless very confident of the outcome as it may cause severe damage.
Further advice on locomotive maintenance can be obtained from members of the SMRC, several of whom have many years experience in maintaining model railway locomotives and multiple units. Please contact the club if you require further details.