Entry posted by D869
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Owners of Farish class 47s circa 2008-2010 will probably have read lots of words on RMWeb about the shortcomings of some batches of this loco. I am the proud (ahem) owner of one of those models - D1764 in two tone green with full yellow ends. This loco has been on the St Ruth roster since the 2010 Expo in Oxford and has, shall we say, never been a favourite with the operators, it being fiendishly difficult to get all 6 axles reliably on the track and seemingly having a remarkable ability to skip the rails even on those occasions when the hapless driver does manage to get it railed up correctly.
It's pretty well known that there are two major issues - the bogie outer sits too low and the loco body sits too high. This posting is about the first issue.
The simplest fix was done a long time ago - the bogie has mouldings underneath each axle gear which on my loco fouled the track when passing through pointwork, dumping the loco onto the dirt. The outers were unclipped and some big flats filed on the mouldings under the gears, leaving just the thinnest amount of plastic beneath the gear - holding it up to the light is a good way to judge this when filing. The guard irons were also pretty low so these had some plastic shaved off too. These simple mods were of course a huge improvement but after several more shows, its fair to say that this loco's record has been pretty mixed - some shows being spent entirely sidelined because it was still a pain to put on the track and its tendency to derail hadn't been entirely cured either.
In the past few weeks I've decided to have another look at D1764 ahead of the Epsom show to see if I can cure it once and for all of its antisocial tendencies. The first step was a thorough reading of the various words posted on RMWeb, followed by a close inspection of the bogies with vernier calipers to hand. My conclusions were much as others have said - not only does the outer sit too low but all of the axles have too much vertical play. These two factors account for the difficulty in putting the loco on the track - the low sideframes mean that you can't see the bottom of the wheels comfortably while the wheels flopping around all over the place add to your difficulties when trying to put the thing on the track.
The first step in solving these problems is to shave some plastic off the bottom of the bogie inner. This is straightforward enough but not quick.
I decided that the outer axles had about 0.4mm of vertical freedom so I would remove this amount from the bottom. Before doing this the bogie has to be fully stripped down - a soldering iron to heat up the pickup sufficiently to soften the melted plastic pins that hold them in place and then push all of the gear pivots out (from the side that has a slight taper). Do this aver a tray - you cannot afford to lose any bits to the carpet monster! Finally I cleaned the grease off the bogie to stop it attracting filings. The bogie was then filed in stages, trying to get one section down to the right dimension, then another and finally joining all of the filed sections. In my case I was looking for 3.7mm high at the ends and 4.7mm where the first 'step' is.
The photo below shows the first stage of filing the bogie - look at the left hand side between the axles.
After thoroughly de-burring the bogie and cleaning all of the filings off by shoving Blu-Tack into it from every concievable angle I started reassembly, again over the tray. I found a handy way to get the pivots started back into their holes - hold the knurled end in a pin chuck and then push them in from the side where they are the tightest fit. When just protruding into the inner cavity, add the gear and then finally (free from the pin chuck) push the pivot fully home.
Before refitting the pickups I added some wipers for the centre axle from 36SWG phosphor bronze wire... more on the centre axle later.
The second problem that needs to be solved is how to persuade the outer to sit higher up. All the work so far has created the space for it to do so, but has done nothing to make sure that it will happen. I tried just re-fitting the outer and found that it was now possible to rock it from side to side... not what we want. I wasn't able to find much detail on how others had done this. My first attempt was to try to push the clips on the inner upwards by melting them with a soldering iron. The main result of this was the removal of a lot of the plastic from the clip - I don't think it really moved much at all. The second (and so far final) attempt was to add a piece of etch waste bent into an 'L' shape so that the foot of the 'L' sits in the slot above the clip. This had the desired effect but it makes the bogie rather a pig to assemble as well as deforming the outer a little. Suggestions for better solutions will be very welcome.
Here's a photo of the bits of etch scrap in situ
Finally a comparison photo of a bogie that's been 'done' (left) with one that hasn't (right). The difference is not hugely noticeable but it is there. There is also a lot less vertical play on the axles of course, but you can't see that in the photo.
Initial running trials on South Yard have been successful but that's not a great test because the loco has passed tests there several times only to disgrace itself on St Ruth. It might get a run on St Ruth tomorrow.
And finally... even with this modification the bogie still has some... err... character. As has been noted by others, the centre axle has more vertical play than the outer ones. You might think that the only concern here is that the wheels can flop around too much (which they can) but there is another problem. If you watch the loco carefully when running back and forth you will see that the centre axle will lift without any provocation from the track. The reason for this is that the centre axle is also part of the gear train to one of the outer axles, so the torque transmitted to the outer axle forces the centre axle to either the top or bottom of its range of movement. The result is that one bogie will always have its centre axle lifted, depending on the direction of travel. This could well be the reason behind some of the derailments. Shaving 0.4mm off the bottom of the bogie has reduced this problem but because the centre axle started with more play it still has some movement. The loco also has the 'body sets off before the bogies' issue when reversing direction. Oh well, one problem at a time!
Oh, and if the loco starts to behave itself better then it might get treated to a lower body, some weathering and so on.
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