Splitting Headaches and a Split Chassis – a bad combination (or why split chassis DCC conversion is VERY Hard!)

This weekend has allowed a good amount of time for working on the layout and projects.  In hindsight, it should of been a good opportunity to simply operate the layout, as having caught some serious man-flu; coughing, headaches and tiredness meant full concentration wasn’t on the cards.  I should have sat back with a cup of tea and watched the trains go by; but I did not!  I really wanted to start and complete a project.  Unfortunately this wasn’t to be!

One of the remits of this blog was to share modelling mistakes and today’s post follows this promise with the admission of defeat!  Having received the latest Bachmann Collector’s club magazine I had read through it and found an interesting article on converting a split chassis locomotive to DCC.  Although I had absolutely no good reason to attempt this myself; after reading the article on converting the Bachmann J72; it seemed achievable.  I’ve always liked the look of the J72 and found a very cheap example on ebay of preserved J72 69023 Joem and having a spare old R8245 Hornby DCC chip I thought; why not?

I did a little research on the model beforehand and found on a forum someone advising another person to not bother trying to convert the Bachmann J72 to DCC.  I wish I took that advice as easily!  I knew it would be a challenge; but then also thought it achievable.  Going back three years ago; I didn’t know how to fit a DCC chip in a DCC ready locomotive; but I now have experience of converting conventional non-DCC loco’s – Hornby terriers, Duchess, West Country, J94 classes, also the Bachmann N class, Austerity 8F, without any training or knowledge of soldering and a D grade GCSE in DT from many years ago!  Given this steep learning curve, I thought a split chassis DCC conversion was the next step…

For those who do not know; converting a split chassis model is difficult due to how it is constructed.  The model underneath the plastic body is effectively two chunks of metal; literally split down the middle by insulated plastic.  The two metal frames have direct contact with the wheels, with the wheel sets having insulated bushes to prevent shorting.  The theory behind the construction was simple – you need no wiper pick-up’s on the wheels and no circuit boards or wires at all. The principle wasn’t a bad idea in pre-digital days, although in practice it varied in how effective it was.  Having such large and heavy lumps of metal separated by plastic can often lead to weaknesses and cracking at critical points.  The designs varied in terms of their longevity and performance – some such as Bachmann’s Lord Nelson class having a pretty good reputation whereas their old LNER B1 split chassis version was terrible, by all accounts.  Bachmann are slowly upgrading their split-chassis to more conventional types (the LNER B1 being a recent and welcome upgrade) but these updates take time and money.

Unfortunately the only way to add a DCC chip in between a motor and a live body frame is by performing some surgery to bore out to access and isolate the motor.  The motor on the J72 is buried in metal and required some sawing, milling, drilling and filling for it be accessible for wiring.

To protect the smaller parts, the whole chassis has to be dismantled.

Once dismantled and cut up, it the chassis has to be wired to a DCC chip.  This introduces wires into a design that was meant to be wire-free so you’ve got to be sure you insulate everything carefully and you need to factor in this consideration to create enough space at the chassis surgery stage.  The same goes for the DCC chip; which will need an insulated home.  On tender locomotives, the tender is often a good location.  So far, so good, or so it seemed – the motor could be accessed and space was carved out for a DCC chip with just simple wiring needed to take place before re-assembly.

At first it seemed that I’d got it right and the partially reassembled chassis worked – it went backwards and forwards a couple of feet.  It needed some tidying, but on the whole was OK, or so I thought.  However, the rebuild was slightly flawed and the alignment of the two chassis halves wasn’t perfect.  It was literally a couple of mm’s out of what it could tolerate and although barely noticeable it meant that after tidying up the wiring, the fully re-assembled chassis wouldn’t budge.  The cog’s were out of alignment between the wheels and the motor.  It required a full dis-assembly to find the cause of the slight misalignment, but I never anything obvious, except a little too much insulation.  It soon became apparent that the dis-assembly had created problems of it’s own and the misalignment was more pronounced on the re-assembled chassis.  The final straw came when one of the cables from the Hornby DCC chip popped out.  The cables are held on to Hornby DCC decoder’s by a tiny dab of solder and can be talked loose.  With so much handling, a wire coming out was only a matter of time.

So what next?  All is not completely lost.  This J72 could still be DCC chipped; the alignment issues could be sorted by a few new plastic spacers and screws.  The motor frame is open and ready to be wired.  A new chip would be needed of course and a better one than the one before.  However, I’m hesitant to do this, as it would be so easy to make another mistake and for it to start costing silly money.  So for now; J72 69023 Joem is being put on display, pending a future review.  In the meantime there are more pressing projects; the main one being to get well before contemplating anything so complicated!

In summary and in answer to the question of whether DCC conversion of split chassis’s is possible – the answer is yes and Locoyard’s Bachmann 850 Lord Nelson is the proof of the pudding.  However it is significantly harder than re-wiring a conventional DC model and a simple error can lead to bigger problems; so the possibility of conversion goes with the caveat that you have to be very competent and confident of what you are doing.  If you are not; don’t bother – it really is not easy and not worth the hassle.  Hopefully this entry explains why conversion of a split chassis to DCC is so difficult – fundamentally adding wires and a circuit board to something specifically designed to not have either of these things is always going to be difficult and can lead to unexpected problems including ruining circuitry, balance and alignment.

2 thoughts on “Splitting Headaches and a Split Chassis – a bad combination (or why split chassis DCC conversion is VERY Hard!)

  1. Thanks for this, we were actually just looking for internal photos, but very interesting and a useful caution.
    My son reports having seen a J72 permanently coupled to a wagon with wires going between the two… perhaps this could be one way around the problem, if it is indeed worth solving at all.


    • It’s a possible solution to the problem of finding space for the decoder, but doesn’t get away from the need to grind away metal to get to the motor contacts and re-assembling the chassis afterwards. I’d say that is the hardest part and if you can do that, removing some metal to create space for a decoder shouldn’t be an issue.

      Good luck if you do attempt it, I hope it goes better than my attempt!

      All the best,



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