Modifications to the Heljan Class 14

The Heljan Class 14 as supplied

The Heljan class 14 is a model originally commissioned of Heljan by Hattons, but now available as part of the standard Heljan range. Like many RTR models, there are a few modifications and enhancements which can turn an already superb looking model into something even better!

D9500 arrived at Ashprington Road in late February 2010, being the first release of the model. It has been a reasonable runner, but hasn't been used much as it has been waiting its turn for chassis and weathering improvements - the subject of this article.

The Chassis

One aspect of this model which has always given me concern is the way it 'waddles' and 'clicks' as it runs. I believe that there are two reasons for this:

  • The incredible amount of side-play in the axles, something which I identified in my Review way back in 2010
  • Some kind of issue with the coupling rods clicking
  • The general 'top heaviness' of the model due to all the weight being located above the footplate instead of integrated as part of the chassis block below the footplate

The author believes that the chassis design on this model is far too unnecessarily complicated for what is a very simple 6-coupled loco. The designers seem to have had an aversion to the solid chassis block method used by all other manufacturers on small locos like this. As a result, this model has been compromised with 'top heaviness' and assembly problems. A single chassis block for the full length of the loco, padded out to the correct width and no need for a plastic facia, would move most of the weight below footplate level and this in turn, would have freed up space for wiring, decoders and speakers above footplate level.

For manufacturers, the issue of side-play has always been one of finding a balance between reallism and facilitating running around tight curves. Historically, the centre axle of a 6-coupled locomotive has often been given a little more side-play than the outer axles in order to facilitate this, however, with short wheelbases, it is debatable how much side-play is necessary.

The side-play on this loco is the largest I have ever seen on a 4mm scale loco at around 2mm, way beyond excessive to the point of being rediculous. Someone got some measurements fundamentally wrong! The side-play applies to all four axles, including the jackshaft axle which is narrower than the wheeled axles, evidenced by the coupling rods being significantly out of line with those attached to the wheels (they should all be exactly in line):

Our EM and P4 friends must have lots of fun with this where they have an extra 2mm on top of the 2mm I am seeing!

I set about thinking of ways in which the side-play could be limited, at least to the two outer axles and the jack shaft.
The model has no proper brass bearings, so these can't be used as solution.
I also wanted to avoid a solution which meant removing the wheels from their axles as I didn't want to upset the quartering. This of course, meant that a solution could not involve threading extra washers onto the axles.
This left me with the idea that the way forward would be to increase the width of the chassis.

When the model is dismantled, it can be seen that the plastic chassis sides have 'pseudo' horn guides moulded and this gave me the idea that they could be used as a way of retaining some extra packing. I came up with the idea of making some plastic parts which would fit in the 'horn guide' recesses. Using plastic card, I made up a template 'master' to test the idea. Finding that it worked, I asked SWMBO to draw up a design in her 'Matrix' Jewellery CAD software which I would then 3D print in ABS plastic:

The following images show the first spacer having been fitted on the right-most axle:

This highlighted a problem: The plastic on the chassis is actually a decorative facia to a metal internal chassis - nothing wrong with that, plenty of other manufacturers do something similar. However, on this model it is made from that cheap, nasty 'nylon-like' plastic of the 1970's which no glues will stick! Many modellers will probably have noticed this when they found that the brake blocks fell off when glue didn't hold. One can see that the designers of this model were aware of the problem because of the crude way they have attached the plastic to the chassis - this is marked with red circles in the image above showing the axle side-play. Note the extruded plastic 'nodules' just below the gears - the plastic has been pushed through the metal and then melted to hold it in place.
I used a file to rough the plastic surface and then used Superglue to glue the new 'horn guides' into place on the two outer axles.

The Jack Shaft

Having attended to two axles, the next item to be attended to was the Jack shaft axle. The moulding on the chassis facia has no recessing around this, which meant that I had to consider how a spacer could be attached. Attaching spacers/washers to the jack shaft would be even more of a problem than the wheeled axles because the fly-weights on the ends appear to be very solidly attached. With no retaining or recessing, there was no way that spacers would stay permanently fixed to the chassis facia, so I decided to go down the route of attaching spacers to the actual jackshaft. To do this, I filed down two plastic discs, 5mm in diameter and 1.2mm thick. I drilled a 2.5mm hole through them and then cut them in half. I then wrapped the two halves around the jackshaft and plastic welded the 'washers' together again. I then used Superglue to secure the 'washers' against the backs of the fly-weights. The plastic was then filed down a little and slotted into the chassis perfectly with no side-play or 'tightness'. It will be lubricated later.

Test Running

With the two outer axles and the jack shaft now 'retained' I gave the model a test run. As expected, there was a little tightness, so the new 'horn guides' were slightly filed down such that the corresponding axle had a little movement to accomodate uneven track. Once this was done, running was much improved with no 'waddle', however, because the centre axle was still unrestrained, it was able to move about and cause uneven running.
New 'horn guides' were duly fitted to the centre axle, exactly the same as the outer two axles:

Further test running found that the centre axle requires some side-play, even to get around the sharpest curve on a peco large radius curved turnout, therefore, the centre axle 'horn guides' were filed down by about 0.3mm each.

The chassis was then reassembled:

Filling the Chassis Frame Gaps

For some strange reason, the chassis frames stop short of the backs of the buffer beams by 6mm on both ends of the loco! Cameras are unforgiving and any track level side-on photography is highly likely to expose this problem. I resolved it by glueing strips of plastic card to the existing plastic, shaping them to fit the back of the buffer beams. Notice also how at this stage, I have commenced painting, including the pickups which previously stood out glaringly when the loco viewed side-on:

Filling the Buffer Beam Holes

Consistent with the 'demand' for NEM coupling socket compatibility, this model has had its buffer beam compromised in terms of a hole through which the coupling fits.
It would be handy if the model was supplied with blanking strips to fill these holes.
Since I use prototypical chain couplings - those supplied pre-fitted on the model are perfect - I filled the holes with strips of plastic card which will be painted yellow later:

Due to the inaccessability of the buffer beam due to all the details fitted to it, it will be very difficult to hide the joins around the filled in panel. Maybe during painting, the joins with fill with paint, but I'll probably just have to accept that this is a 'panel'. At least it is better than a hole which doesn't exist on the prototype.


With the wheels removed, I painted the chassis sides, including the 'gap fillers'. Later, the bearings were lubricated and the chassis re-assembled and the wheels painted:

New Decoder

D9500 has been running with a TCS MC2 decoder since it first arrived on Ashprington Road. Since then, I have been progressively replacing TCS decoders. I find that TCS decoders just don't quite give the fine controllability that I look for. At one time, they were good decoders, but today, they are really mid range decoders as there are several other brands which produce much better decoders with much better finesse in control at not much greater cost. These days, my decoders of choice are either ESU or Zimo. To that end, a Zimo MX600R was ordered. Admitedly, I should have checked sizes beforehand, but needless to say, it was found that the space in the loco was too small to accept the decoder - another design fault on this model. I have no idea how anyone fits a sound decoder with a standard speaker!

Time to Take Stock

When I discovered that the decoder wouldn't fit, I decided to investigate the options to make it fit and in doing so, re-familiarised myself with the numerous manufacturing and design faults that this model has:

  • The nasty plastic used on the chassis has now become infuriating: bits keep falling off and have to be repeatedly glued
  • In dismantling the chassis, the wiring loom is so tight that it is impossible to dismantle without accidently disconnecting wires to the lights...
  • ...The lights are hidden behind the chassis such that they are inaccessible with a soldering iron...
  • ...and the plastic body is assembled around the chassis such that it cannot be separated from the chassis to access the lights without having to break it off. It should be possible to undo a couple of screws at each end of the model and for the body to lift off in its entirety, leaving a completely self-contained chassis - the same as every other manufacturer does this
  • There are screws in the cab which secure the body to the chassis. These do nothing more than create an undulating footplate which looks awful - massive assembly problem which yields itself as the cab not sitting firmly or level on the footplate. This happens because there is no continuous flat-bed for the the footplate to fit on. It sits on top of the chassis at the ends and around the cab, it fits under the cab so it is pulled down at the ends and up in the middle and the wiring competes in the middle. Net result is an undulating footplate. This is an extremely poor design
  • The wiring loom relies on very tight channels which are almost impossible to re-thread, making re-assembly extremely difficult, compounding the 'cab screw' issue. The cab cannot actually be fitted unless the wiring is pushed into extremely tight recesses. This is completely unnecessary
  • I had observed that the uneven running in one direction exhibited a wheel 'lifting' (observed as wobble) on one corner. I suspected that the chassis may not be square, however, it turned out that the lifting was caused by the inability of the keeper plate to hold the axles in place and that the wheels were actually square on the track. This would be resolved if a screw-fitted keeper plate was used instead of the clip-fit arrangement. But that isn't possible because there is no solid chassis block to screw into
  • In tracking down the 'lifting' on one corner I thought I had better check that my new 'horn guides' weren't actually affecting the positioning of the axles in the chassis. It turned out that they were positioned sufficiently above the axles not to affect them, but in the process, I discovered that the axles are not actually running in the metal chassis 'bearings'. They are actually running on the plastic chassis facias which protrude more than the metal. Yes, you got it folks - this loco has plastic bearings!!!
  • I finally found the cause of the uneven running in one direction and the 'clicking' which I thought was the coupling rods, but had evaded me finding it. The gear adjacent to the one driven by the motor worm drive has a deformed tooth - since this is essentially a 'sealed' area, this is a manufacturing fault which has existed since I purchased the model back in 2010. The problem is that the shaft which holds this gear is inaccessible and requires the metal chassis to be parted and the plastic footplate (which can't be removed) broken off in order to access it. In other words, this is a pretty much a 'throw-away' unserviceable design
  • The wires protruding below the PCB for the decoder socket protrude into a recess in the chassis block where some insulated tape is fitted at the bottom, but not on the sides of the recess. I am not convinced that this isn't too close so as to cause shorts between the socket pins and weighting block. None of the lighting works on this model now (it did originally), so I suspect that the socket pins may have shorted out the decoder lighting outputs. I'll have to try the decoder in another loco to check. Bottom line is that this extreme close proximity is a very bad design where a decoder socket was clearly an afterthought

In 40+ years of modelling, including scratch-building of locos and numerous brass kit and chassis builds, I have never had a model defeat me. But this one has due to its extremely poor design.
I am now deciding whether it is even worth persevering with this model. It has a beautiful body, but quite frankly, the mechanism is nothing short of cheap and nasty 'throw-away', non-maintainable junk. At best, the only way forward would be to completely replace the chassis with a brass kit.

In further reading, I have discovered that the chassis frames of a prototype class 14 are actually very narrow (12.5mm in 4mm scale) due to the suspension springs being located on the outside of the frames. That said, the Heljan frames measure 11mm so are 1.5mm too narrow anyway. That 1.5mm is not far off the thickness of my 'horn guides'.

I have reassembled the model but there is a significant gap at the bottom of the cab sides because the cab won't fit:

If I tighten up the screws in the cab to pull the footplate up, it will cause the footplate to arch upwards. At this stage, I haven't managed to reconnect the wires to the lighting on one end, therefore, lighting is disconnected on that end.

Having found that one of the gears in the gear train was deformed, I decided to put in the effort to try and remove it in preparation of obtaining a replacement. This is the offending gear:

The malformation is indicated by the red lines on both of the pictures above. It can be clearly seen that there is a variation in gear tooth spacing. When operated manually, a 'binding' can be felt when the mispaced tooth is meshing against the gear beneath. This will be why the loco jerks and possibly, clicks.
The blur lines indicate the 'bearings' within the frame in which the shaft here is retained. Because the bearings are part of the chassis frame, there is no way the gear is coming out the top because this would require the part of the metail chassis frames (impossible to do) so the only way this gear is coming out is by its axle being pushed through from the side to release it. However, this highlights a further design fault indicated by the green line that the shaft is prevented from coming out because the 'nylon' plastic chassis facias (noted previously as being melted to the metal frames) but up against the ends and these in turn, are retained by the inner edge of the footplate. This is a seriously bad design, clearly not designed to be dismantled.
In order to get access the the end of the shaft, I would have to remove the footplate and the 'nylon' facias. The footplate is a single piece moulding which is wrapped around the chassis block area which retains the motor. The chassis cannot come up through the footplate because there are various retainers and the pickups making it too wide to do so. Which means that the chassis must go down through the footplate and the only way to do that is to force the sides of the footplate outwards to allow the chassis block to pass through. I managed to achieve this without breakage.
This is how this model has to be worked on because the whole design is tied up like a spider's web by the wiring, none of which can be disconnected because everything is soldered and there are no pluggable connections:

I then commence pushing the gear shaft from the lower end. It's a reasonable tight fit, but it can be pushed through. The 'nylon' facia becomes an issue, but I decided to force it anyway (indicated by green line) and eventually, the shaft can be removed:

Here is the offending part for which a replacement will be obtained:

The malformed tooth can be seen to the left of the 'dirt spec' (introduced during removal) and aligns with what appears to be an injection moulding point on top of the gear. The tooth points slghtly more to the left than it should, creating a smaller spacing on to the left of the tooth and a larger spacing to the right, thereby contributing to even running.

I made contact with Gaugemaster who are the appointed spares agent for Heljan in the UK. Gaugemaster advise that they have no replacement mechanical parts such as gears for the class 14.
I now have a £110 model with a manufacturing defect in a critical part of the mechanism for which the replacement part is not available. It is looking like this model is not repairable.

Following contact with Heljan, Gaugemaster (the authorised Heljan part dealer) and Peter's spares, I have found that replacement gears for the Heljan class 14 are not currently available.
Ultrascale can make one for £50.00. Sorry, but I think that is a little excessive for one gear. And I think an 8 month delivery schedule is totally unacceptable.
Heljan have advised that a new run of the class 14 is being produced in early 2022 and have asked that I wait until that run when new gears will be made.
I have therefore relegated this entire dismantled model into a tray and put it on the shelf. Nothing more can be done with it until early 2022. Great!

Heljan advise that they are awaiting samples of the new batch of class 14's. Once samples have been received, they will have a better idea of timescales for delivery.

More to follow.

Related Articles

Review of the Heljan Class 14
Introduction to Weathering
Weathering Locomotives
Index of Articles

Graham Plowman (Created 20/09/2021, Modified 18/01/2022 5:57:39 PM +11:00)

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