Adding a smoke generator to a model locomotive is a very popular enhancement, and although it doesn't necessarily look 100% prototypical, it adds a whole new dimension to the model, not to mention a smile to the beholder!

YouChoos uses Seuthe smoke generators for fitting to OO steam locomotives. Either Seuthe #27 or #22 are generally appropriate as these have a protective sleeve that at least gives the plastic-bodied model a chance of surviving the high temperatures. Other suppliers provide similar products, and can sometimes even provide a bespoke smoke generator for specific models - First Class Trains is an example, who provide custom-made smoke generators, as well as Seuthe-like units.

Beware though, that prolonged use of a smoke generator could cause some warping, misshaping or melting of the plastic of your prized model!

Various steps can be taken to reduce and avoid this risk though, and that is the purpose of this guide.

Firstly, investigate the space you have available beneath your loco's chimney - is it deep enough to take a Seuthe unit? Seuthe #27 is a couple of mm shorter than the #22 so it may be more approprate in some models. If there isn't enough space, you may consider grinding some of the chassis to create space. Beware not to take too much away though, or you may compromise the loco's ability to stay on the track - particularly if the loco has light-weight front bogies.

A loco with a short chimney, such as an A3, Duchess, or West Country Class is a good candidate for smoke. Generally, the taller chimney that a loco has, the more difficult it is to add smoke. In some cases you can actually remove the model's existing plastic chimney and use the smoke generator itself as the new chimney! YouChoos has done this to great effect on Bachmann Jinty and Hornby Thomas models.

If you are particularly worried about the plastic chimney becoming misshapen, you could consider replacing it with a metal one instead. Such replacement chimneys can be obtained from a variety of sources, such as South East Finecast, Alexander Models, Alan Gibson Workshop etc.

Assuming the chimney is wide enough to fit the smoke generator (file some extra diameter out if need be), you can simply insert it into position, ensuring that the top of the unit is flush (or marginally lower) than the top of the chimney, then glueing into place using a high-temperature resistant glue, such as DevCon's 5-minute 2-part epoxy. Put glue right around the join where the smoke generator meets the loco body, which will give support to the model's boiler, and dribble a very small amount down the outer case of the unit on one side and under the base (but only a thin streak) - this will help to support the smoke generator and stop it from 'sinking' in the tubing later. However, do NOT cover the whole smoke generator, or the entire base where the 2 wires come out, or the unit will have no way to breathe or dissipate heat.

DO NOT let ANY glue go down into the smoke unit!

Smoke generators normally have just 2 wires, which can be connected to your decoder. It doesn't matter which way around you connect them, although YouChoos tends to stick to the convention of using the unit's BROWN wire to the BLUE positive wire of the decoder. You do NOT need any resistor (if you do, you'll probably get no smoke!). The other wire connects to an output wire of your decoder - YouChoos normally uses the PURPLE (4th) output wire for this purpose, although the GREEN will also work just fine.

Check that your decoder is up to the job of supplying the power required to operate the smoke generator (anything from 70mA up to 180mA). As an example, the CT SL51-4 decoder has 8 function outputs, but only the 1st 4 (WHITE, YELLOW, GREEN and PURPLE wires) can supply this amount of power - the other 4 outputs have reduced power which are ok for LEDs but not enough for smoke. Check your decoder's manual to see if it is capable. Note that the standard Hornby decoder does NOT have enough power to run a smoke generator.

In extreme cases you can use a miniature relay which takes power directly from the pickups, but uses a decoder function output to switch that power on and off. This then protects the decoder from overload. However, it is just another component for you to squeeze in somewhere, and you'll have to learn how to wire the relay up too!

In general, don't try to install dual smoke generators into plastic bodied locos - these combined will produce sufficient heat to melt the plastic quite quickly, so unless you are prepared to take the risk, stick to a single smoke generator in the front chimney of double-chimney locos.

Below is the pretty Bachmann Wainwright C with its new metal chimney (supplied by South East Finecast) fitted, complete with Seuthe smoke generator, ready for treatment with the airbrush...