Fitting a Lenz 0511 DCC Decoder to a Bachman Farish 8750
There are two major questions to ask before tackling this job, how to isolate the motor from the chassis and why would anyone in their right mind would want to try.
The first question is now very easily answered thanks to Gerry Spencer (Member 13358) who has come up with a conversion kit. At first sight this looks expensive at £8.50 per loco but it is a very high tech piece of kit indeed. Open the package and you get an insulated brush holder and a brush clip with sleeving on each arm. And a drill. That’s simple, I could do that. But it’s not simple, I gather that the insulation on the brush holder is, I think, “spun polymer”, and has to be of sufficient thickness not to break down due to the high frequency signal, but not so thick that the hole needed in the chassis would weaken it too much. And the sleeving on the clip is to aviation specification which allows you to solder a lead to the clip itself.
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Buy these from Gerry or from Osborn’s Models. Oh, and I’m told the drill is an odd size too. No instructions are included (hint to Gerry?) but read on.
Do not attempt to fit the conversion kit yet, you will be ill-treating the chassis and it will need all its strength. We start with the body and the most worrying part of the job, especially if you are modifying one of the lovely lined BR locos.
Where to put the decoder.
On my first attempt I thought of putting the decoder in the cab roof, but you can see it through the cut outs and on the 57XX versions it would be even more visible. The only other place that seemed possible was the bunker.
The cabs are plastic and will come off. With care. Remove the chassis and put it well out of the way of all the mess you are about to make. Inside the cab you will see that the rear splashers cast into the main body are hollow. Very carefully push the bottom side of the cab side outwards from inside the splasher with a small screwdriver or similar. Some cabs seem to be glued on better than others. Patience and courage will be rewarded with a gentle click as the sides pop out of their locating groove. Or a not so gentle crack if you push too hard. Little and often will eventually break the bond. Gently pulling the cab upwards with very careful levering will remove the cab. Now we need to make the cab an easier fit by scraping or filling the inside and rear of the locating ledge on the cab front until the cab slides on and off but is still retained by friction. All will be explained.
Remove the dummy coal by carefully running a scalpel blade or similar between it and the bunker. Again some are glued on better than others. File the bottom of the coal flat and cut out the top of the bunker where the coal sits. This is needed because there is only just enough height for the decoder even with great chunks of chassis removed. By scraping and filing, thin the back of the bunker (from inside of course) as much as you dare. And then a bit more. Space really is at a premium.
Modifying (hacking?) the cast body.
With your favourite instrument of torture, slitting disc, dental burrs, file, razor saw, axe etc. remove the cast inner part of the cab from just behind of the forward square indentation and nearly, but not quite down to footplate level. Make sure you leave the little arc of splasher in place to retain some strength Grind or file out the rest of this that is inside the footplate, including the web inside the steps. (This is more obvious in the photos or with a loco in front of you). Grind a shallow chamfer inside the cab front/ firebox junction. This gives a bit more room for the leads to be tucked out of sight.
At the sides file down the remaining ledge flush with the top of the footplate but at the rear leave a wafer thin ledge either side of the chassis mounting slot to locate the chassis and the cab back. Tidy it up, smooth and repaint any bare metal or damage.
Mistreating the chassis
Take the chassis apart, best done inside a plastic box or large plastic bag so that nothing gets lost. Once the motor mounting screw is removed the motor will slide out forwards. And the lower brush and spring may try to leap into oblivion. Remove the lower brush clip and mounting.
Some of the wheelsets (even the new ones) are not quite perfect, if your loco ran well before modification make sure you keep the wheels in exactly the same order and orientation. If it waddled they can sometimes be improved by swapping around and turning round. Sometimes, sometimes it makes it worse.
Remove the capacitor if it hasn’t already fallen out. File the back of the chassis forwards and down removing the capacitor slot and a bit more and leaving a wafer thin tab to locate in the rear of the body. Be brave, take out as much as you dare and file a bit off the plastic back of the motor as well.
If you put the chassis block back in the body and refit the cab you should have a clear space in the bunker into which the decoder will just slot.
Making a connection
You have now lost the electrical connection to the chassis block, it was the capacitor lead. I drilled a 1.6 mm hole through the chassis block to take a very small self tapping screw.
Carefully drill out the hole for the insulated brush holder using the drill provided. Do not drill by hand in a pin chuck, use a mini drill or hand drill as this will ensure that sufficient material is removed. Believe me there is a difference, I’ve tried both ways. Drill carefully as the hole breaks out into the shaped part of the chassis for the armature. I’m not convinced whether it is better to drill from above or below. The brush holder should be a good but not tight fit. Before you fit the brush holder decide which way you are going to take the lead from the clip and file a chamfer on the rear corner of the cut out so the lead will safely clear the rear wheel. (Genius has just struck, chamfer both sides and you have a choice).
Repaint the chassis where needed.
For some strange reason the brush seems to fit better from inside than outside. Put the insulated clip over the brush holder ensuring it is a good but not tight fit. Take care not to damage the sleeving. Fit the spring and brush and re-fit the motor. Either use a rubber band or temporary screw and nut to secure it at the front. Hold the decoder to the back of the chassis with the big chip against the end and the leads to the left. Cut and strip the orange lead and solder it to the insulated brush clip, make extra sure that the bare wire cannot touch the chassis. Take of the rubber band or screw and fit the wheels and keeper plate assembly. Fix at the front with the mounting screw and a spare nut (8 BA). Cut, strip and fix the red lead to the chassis, I took it over the top of the end of the motor and down the right hand side to keep it clear of the orange lead. Remove the lead from the motor fixing nut to the upper brush, solder the grey lead to the upper brush and fix the black lead to the motor mounting screw and nut.
Put it on your programming track and check that all is well.
Remove the temporary nut from the fixing screw and fit the chassis to the cast body. Cut a rectangular section from a good quality plastic bag about the size of the decoder and slip it over the decoder with the openings at the top and (of course) the end where the leads are. Tack it to the decoder with a spot of non solvent glue. (Thanks to Gwyn Humphreys 3293 for that tip.) Trim back and insulate the spare lighting wires – anyone know how to do loco lamps in this size? Carefully bend the decoder wires so it fits across the back of the chassis.
Now you will realise why I made the cab removable. Holding the decoder against the end of the chassis slide the cab in place so that the decoder is in the bunker. If you have removed enough from body, cab and chassis it will just fit inside the bunker.
Refix the dummy coal load with a non permanent glue as I think if you need to take it all apart it will make life easier if the decoder can be pushed down while the cab is pulled off.
Test it all again on your programming track. Now, any suggestions for some good settings to suit these little locos?
I’m sure (in fact I know) at least one other person has fitted decoders in these locos. How about writing it up for the journal? Your method might be a lot easier – and I have one more to do sometime!.
Mike Page-Chestney 13822
PS Anyone interested in a Area Group in the Immingham area?