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Another RTR conversion at Honley Tank


Dave at Honley Tank

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The K3 conversion is complete. At least the engineering bit is complete; the re-numbering and early BR totem, plus a bit of weathering, remains to be done.

 

Although I've done a fair bit of lathe work on this one, I think it can be described as an easy conversion for any one willing to buy and assemble a new set of valve gear and a set of Gibson wheels. I wasn't!

 

Years ago, just after Bachmann introduced the W-D, I converted one of those, and reported back that it was not such an easy conversion without the help of a lathe. The K3 was very similar.

 

In both cases my reluctance to spend more cash meant that I wanted to retain the Bachmann coupling rods and valve gear, they are after all commendable bits of modelling. Unfortunately the crank pins of the Bachmann wheels are of much larger diameter than those we modellers normally use and which are readily available from various traders. I have been told that now-a-days Gibson retail a set of brass bushes with which to bush the Bachmann rods, but I have no experience of these

 

I turned up a new set of crank pins of a diameter to match the Bachmann ones. (dimensional info. in sketch below). I went much further with the lathe work for the K3 as compared to the W-D because, apart from the drivers, I re-used the Bachmann pony and tender wheels.

 

However these were thinned down from the Bachman 0.120" thickness to the EMGS suggested 0.090". Assuming you have a good set of step chucks, or you make a suitable pair of same, then skimming 0.030" of the wheel front is a doddle and for EM there is not the need to reduce the flange height; P4 would offer a greater challenge, - but that's not rare!

 

The pony needed a new axle ( 2mm silver-steel ) but I re-used the tender axles. The driving wheels could also be done like the others but the crank pin boss would need re-building after skimming so I chose to use Gibsons.

 

Unfortunately the Bachman wheels are a bit under-sized (but within normal wear limits), while the Gibson replacements are spot on size for a brand new wheel. The difference is not far short of 1mm and it results in the Gibson flanges gently rubbing on the Bachmann running plate, and as this is metal, intermittent short-circuiting does not allow good running!!! I raised the body with some 0.030" plasticard packers but this also raises the buffer centres; I think within tolerance, but events may prove me wrong.

 

The chassis width (across frame outer faces) is of course too narrow, leading to excessive wheel side play. On the W-D I made cosmetic main frames to cope with that problem, but because there is some lovely detail on the K3 frames I decided on spacing washers this time.

 

The driven (middle) axle had 0.078" of washer (3 washers supposed to be 0.040 +0.020 +0.020!?!), and this is giving about 0.010" play. These washers are on the gear wheel side, the position of the gear wheel helping the limitation. The front axle being between the cylinders must have its side play fairly tightly controlled too; -this has a total of 0.060" on one side and 0.070" on the other and feeler gauges suggest there is now 0.006" play. Because of the valve gear those amounts of side play are about as sloppy as we dare go without having fouling problems. I may have gone a bit too far in restricting the rear axle to 0.015" play, with 0.1" on one side and 0.090" on the other. Test running on my EM layout has been OK but on Arnold Bellfield's '˜Bodgers Brow' the K3 was not too happy on the tighter turn-outs.
The sketch and pics show the new crank pins
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Dave, I don't have a lathe but found that converting the Bachman WD was simple. The trick was to buy a set of WD coupling rods from Alan Gibson. They were spot-on for the Bachman chassis - top marks all round and, of course fitted the Gibson crankpins perfectly. I forget how I bushed out the conn rod - probably a short length of copper tubing bashed out with a hammer to expand it into the large Bachman hole, then drilled and reamed to fit the Gibson crankpin. Sorry if that makes you cringe, Dave, but it's typical of my bodger's approach - and it resulted in a smooth and slow running heavy goods loco. False black Plasticard cosmetic frames completed the main surgery and Brian (Windermere) Lewis's bit of sound trickery has given it a lovely WD clank when it's coasting.

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