Fitting DCC Sound to a Lima Class 117 DMU

This article describes the process of fitting DCC sound to Lima class 117 DMU, together with some detailing:

Sound Decoder

My sound decoder of choice is the excellent ESU Loksound:

These decoders are a single package, combining traction control with 4 functions and sound. They are back-EMF decoders and provide excellent control. Because the decoders integrate traction and sound, the sound is properly synchronised with the motor operation.
The ESU decoders come supplied with a speaker and a baffle box into which the speaker fits. Wherever possible, I try to fit the larger ESU 40x20mm speaker and a bass-reflex speaker as this combination gives better sound reproduction. However, on this model, there isn't enough space for a bass-reflex and surprisingly, the sound recording actually sounds very good with a well sealed standard speaker.


The Lima class 117 is not a ready candidate for DCC sound, not just because it isn't 'DCC Ready', but because it has such an incredibly noisy motor which would drown out DCC sound! While this particular model is one of the better Lima runners, it can be made to run very well with a decent decoder and decent wheels, motor noise prevents DCC sound being fitted.
If we want to fit DCC sound, we must address the motor noise.
Hornby have not released the former Lima class 117 in upgraded form, however, they have released the Former Lima class 121 and it has an upgraded mechanism which is very quiet and runs extremely smoothly. It is to this model that we look for a replacement chassis:

We believe that when Lima introduced the class 121, they modified the class 117 chassis irreversibly to suit. As a result, the chassis was modified to have a bow end at what was the former corridor end of a conventional class 117 power car. This can be seen below when we try to fit the new Hornby chassis to the Lima class 117 body - note the clip which protrudes too far for the flat ended class 117:

We must therefore file the bow end on the Hornby chassis flat:

A note of caution should be made here because filing the end flat removes the plastic which attaches the back of the buffer beam to the chassis. As a result, it bows inwards. To compensate, we screw fit some plastic support, prior to filing.

Preparing the Speaker Space

To prepare the space for the speaker, we drill holes in the bottom of the weight compartment. The lugs inside the compartment have yet to be removed. We still need to drill a hole for the speaker cable:

We then fit the speaker in place, after drilling a hole for its cable and then fit some of the weights back on top of it and clip the seating back into place:

Fitting the Decoder

Because there is not much space above the motor assembly and because the ESU decoder is fairly long, we must create space by unscrewing the 8 pin socket and moving it towards the front end. We plug the decoder in and sit it on top of the motor housing, suitable retained using insulation tape:

Note the screws on the left end - these hold the plastic retaining in place behind the buffer beams.
While we are fitting the decoder, we also wire in connections to the first bogie of the next coach so as to provide for extra pickups:

Refitting Weights

By removing weights in order to accomodate the speaker, we have lost about half the weight of the vehicle. Therefore, we refit them in the roof above the window perspex. The purpose of the tape on the inside of the windows on one end is to blacken the guard's area windows so at to hide the decoder and coloured wires:

Detailing Modifications

The Lima model is fairly basic in detail, so here we fit Craftsman exhaust pipes, steps, buffers and buffer beam detailing and a driver - in my opinion, DCC sound just doesn't sound right if there is no driver!
The coupling is Bachmann 'EzMate' and is compatible with Kadee.

The Completed Model

The following picture shows the completed model, together with a green version of the same model which has been sound fitted and modified in the same way. At the time of writing, replacement wheels from Ultrascale are awaited for both models.

CV Adjustments

As supplied by Ian Bishop (LegomanBiffo), the decoder requires no CV changes other than the max volume CV (63) set to a volume of personal perefence. DMUs had little more than bus engines and consequently, were not very noisy.

Prototype Videos

Epping and Ongar Railway's Class 117
Driver's Eye View of the NVR between Peterborough and Orton Mere
Barry Island Railway 117 departs Plymouth Road
Class 117 DMU Departs Alresford
Class 117 front seat ride on the Looe Branch July 1994

The Model in Action

Graham Plowman (8/8/2011)

Sound Package supplied by Ian Bishop (LegoManBiffo)
DCKits Logo

ESU Loksound Decoder supplied by:
Howes Models Logo

Bass Reflex Speaker supplied by:
DCC Supplies Logo

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