Classic UK Minitrix Models  -  Mallard
Fix and Clean

Wheels

The main drive wheels will require a lot of attention. First job is to get rid of any fluff, dirt and oil. The running surfaces and the back of the wheels need to be spotlessley clean. Use matchsticks, cocktail sticks or finger nails to clean off the compacted crud that gets onto the surface. A lint free cloth with methylated spirit can be used to help remove greasy deposits. Wipe with a dry section afterwards - don't just leave it to evaporate. Get a hand lens. The axle on the left looked clean to the naked eye and when viewed with a reading style magnifying glass. Only with the hand lens and the camera set in macro mode does the hair/fluff and grease show up. Tweezers, pins, scalpels help to get get stuff like this out.

 

Oil and grease. Only recommended oils should be used. The axle runs in a brass bush and brass is self lubricating. However, a tiny spot of oil applied at the end of the brass sleeve will provide a very thin coating between the two surfaces. I use a very thin oil, pour a little into a plastic tray and dip a pin into it. The tiny drop that forms on the end of the pin is about the right amount.

Now check the quartering.

This is a pretty accurate visual check. Given the amount of play that is built into the design of the holes/slots on the drive wheel coupling rod, this should be good enough. See picture to see how much freedom the coupling rod provides on the centre pin. The same amount exists for all 3 pins.

There are 20 spokes in each wheel, and the screw hole nestles between two spokes. Take a piece of cork or balsa and draw a straight line. Take a track pin or sewing needle and insert it from the inside between the spokes near the screw hole on the side of the axle without the cog. Count round 10 spoke gaps and insert another pin from the inside. Turn the wheel over, and place the point of both pins onto the line. Push them into the cork so that the wheel is held in place. Do the same for all 3 wheels.

 

Having done this, you know that the underside holes are all facing in the same direction. They are positioned on the line. Take a look at the holes on the top. They too should be in the same position relative to each other. Forget the term 'quartering'. A real engine will have one side rotated 90 degrees from the other side to ensure that when one piston is at top dead centre (and can't provide any power to the wheels), the other piston is able to turn the wheels at the most effective part of the cycle. For the model, how one side relates to the other is irrelevant from an operational point of view. (Purists would argue) - as long as the position of the holes relate to the wheels on the same side of the engine. There is a parallax effect in the photo above, but the position of these holes is good.

 

It is possible that the gear has rotated relative to the position of the crankpin hole. (Or more likely, the wheel has turned). A quick check can be made by looking at the teeth of the gear through the gap in the spokes nearest to the crankpin hole. In practice, the slot in the coupling rod will easily compensate for a gear that is half a tooth out of alignment. If you can't turn the wheels on their axles easily by hand, then dont try - they will turn, but forcing the issue will result in a wheel that is more likely to slip in the future.

Check the Gauge.

 

The gauge is 9mm, but what is important is that the wheels go round the track and over points smoothly. Place the wheels on a track. You should feel that the wheels are able to move from side to side between the tracks, rather than being tight against each side.

The wheels also need to go over points. There are two checks here. The first is demonstrated in the photo opposite. The left hand wheel (looking into the photo) is placed tight against the guide rail. Look at the right hand wheel. It is about to hit the apex of the plastic junction where the two rails meet. Not good. The wheels need to be slightly closer together on the axle. Take an axle out of a newish carriage or wagon to confirm the required gap. This axle would be fine most of the time, but occasionally it will derail going over points. Which is exactly what it used to do. I spent ages sorting out issues with points !!!

The other test to carry out is the opposite of the above. Push the wheel axle over to the left hand rail. Make sure that the right hand wheel doesn't foul the inner guide rail.

Electrical Contact.

You may have elected not to desolder the blue wire from the main drive wheel pickups. However, you should be able to lift them from the engine, clean them up and straighten the two arms. Clean the point where the arm touches the wheel - use very fine wet and dry emery paper. Then make sure that the arms are bent outwards so that they press against the wheel rather than just touch it. I don't have a picture of this component, but you can see the arms in this shot of the underside of the chassis.

The front bogie has a shaped copper contact strip which acts as a spring which keeps the wheels lightly planted on the track. However, it also acts as a means of ensuring that the left wheel provides an extra negative pickup for the chassis. This is important because only one of the driving wheels has a permanent negative contact - the other two have rubber tyres.

My Mallard is a Hornby Minitrix Model. My Flying Scotsman is a later Minitrix (not Hornby) model. Essentially they are identical - except in a few small details. When I was investigating what appeared to be an electrical fault in the Scotsman, I discovered that the contact point for the copper spring for the front bogie, had been painted over with the rest of the chassis. (Arrowed in the photo linked to the bottom thumbnail, after I had used emery paper to remove paint.) It occurred to me that this may be true of all later (non hornby) models.

The pictures on the left are all from the Flying Scotsman.

I checked the rear bogie too. The axle sits in a half round slot and is secured by the plastic cover, which is held in place with a plastic pin and a single screw. Remove the screw, lift off the cover and remove the axle. Note that one wheel is insulated where the axle joins the wheel. The axle should be connected to the left (negative) side of the loco, so the insulation should be on the right side. Remember that the loco is upside down when you follow these instructions. In the photo, left (negative) is the wheel towards the top of the picture.

The half round slot was also painted, so there was no electrical connection here either. A small area of wet & dry emery paper wrapped around a watchmakers screwdriver soon made a nice shiny smooth contact. No brass here, so a tiny dab of oil was applied before fastening it up again. Check the continuity between the left wheel and the chassis.

Now check the half round slots for the 3 main drive wheels. Clean them in a similar manner. Blow away any debris.

I checked out my second-hand Britannia model, which had been running erratically. The Britannia uses the same chassis and drive wheels as the Mallard, but the bogie and tender connections are different. Only the live wire runs to the tender. Negative pickup is transmitted through the coupling to the main chassis. However, the Britannia also had all points of electrical contact painted over. These were between the chassis and axles and between the chassis and front and rear bogies. I removed the paint in the key areas and re-assembled, and the engine no longer stalls over points and round some bends as it used to.

There is a brass plate fitted to the underside of the motor which sits on top of the chassis. One tab of the plate is soldered to the contact strip of the motor, and is there to provide the electrical connection between the motor and the chassis. It is worth cleaning up the underside of this strip and the area of the chassis with which it makes contact. I dont have a specific photo for this, but you can see the strip under the left hand end of the motor, and the large blob of solder where the strip is folded up and attached to the lower contact strip of the motor.

Loco / Tender connection. Unlike some locos, there is no need for a spring connection under the draw bar between the loco and the tender. Electrical connection for the chassis is provided through the black wire.

Valve Gear

The plastic slider should slide smoothly. If the metal has acquired a light coat of grime, this may not happen. Wet and dry paper and a wipe of tissue with oil on the slide bars should make the motion nice and smooth again. The photo shows the rear view of the right hand side valve gear, with the slider half off the fixed bar. (Note that as it is now, the slider needs to be positioned to the other side of the pivot arm. Springing the horizontal arm slightly may help to get the linkage rivets to move past each other.

Motor

The motor is a standard piece of equipment and can be easily obtained on the internet from German Model Railway shops. The same applies to the brushes. The brushes have part number 40015400 and the motor is 41207610. Google this number with the word 'Trix'. The german for brushes is Kohlebürsten.

Peer in and see if the brushes have plenty of carbon remaining. Look at quality of the commutator - they may be covered in carbon and need a clean. Dont use anything that will leave minute strands of material. Meths or alcohol may help if it is used to slightly dampen the lint free material you are using to clean.

A tiny drop of oil can be applied to the bearing at each end if it looks as though they need it. Don't oil anywhere else and dont apply more than a tiny drop. It will end up all over the place and possibly ruin the motor. Give the motor a run - the contacts can be pressed against the 9mm track. Check it runs fast and then slow it down.

Tyres


Check the tyres. If they have been on a while, then replace them. Even if they are still intact and not moving, the rubber will harden over time and the wheels will slip as a result. The one on the left has seen better days. Not got any ? The part number is 72087800. The german name is 'Haftreifen'. Put Trix 72087800 into Google. You should be able to get a pack of 10 (10 Stück) for less than a £5 plus p&p. And its not as if they are about to go out of stock. Many current models use the same tyre. I find the German suppliers are fast and efficient, and have more stock than the English suppliers.

This is a comparison - on the left, tyres removed from a late 1980 MiniTrix Flying Scotsman. (Same chassis and wheels as Mallard), compared to a brand new set. The Scotsman was slipping considerably at starts and on gradients. The removed tyres are slightly larger than the wheels, and the rubber has hardened. It turned out that the wheel was spinning inside the tyre. The new tyres look odd - the 'flat' seems to be on the side rather than across the width - but this is how they are, and they stretch into shape around the wheel.

Maintaining Classic UK Minitrix Locos
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