X Class Locomotives

Fine tuning the bogies of an X-Class Models S scale model of an X class loco.

A number of modellers who have bought one of my X class kits over the past six years have commented that the bogies do not stay on the track. If this is the case I am fairly sure I know what is wrong with your bogies.

The radius for each of the radial arms which serve the bogies will not be the same length. The bogies have to sit exactly dead centre in the space of the short concave main frames above the bogies, or below the bogies if the loco is sitting upside down on your workbench. The radius is then measured to a central point just in front of the power bogie. At this point I place a 15mm 8BA machine screw in a 2mm hole. I then measure back to the pivot point centre of the bogie bolster which needs to sit upside down to get this measurement.

On the last X class I assembled, the radius is 30mm for one radial arm but the other one is 1mm shorter at 29mm but you will need to measure yours. It depends on where you drill the hole in front of the bolsters at each end of the rigid 8 wheel mechanism. I make temporary radial arms from 1mm styrene 4.5 mm wide, drilling a hole at each end to suit the two different desired radii until I get it right. The holes in the radial arms should be at least 2.5mm dia to take a 2mm or 8BA screw so it pivots freely, otherwise this will catch which is another cause for derailment of the bogies on curves or through reverse curves such as points.

Also the radial arms should sit as horizontally as possible so that the pivot holes at each end dont catch on the screw. Thus the fairly long screw in front of the drive bolster. Given all this, then the side frames of the bogies should not foul the mainframes below the driver’s cabs.

To provide added weight to the bogies, on the bottom side of the bogies I fit and stick a sheet of lead 35mm x 12mm x 1mm thick on the flat side of the bogie, the side facing the track ballast. Also, the brass bearings need to be at least 13.5mm long so you have slight, but minimal wheel and axle slop.

I have an unpainted X which "flies" around both my track and the Swan View layout at the AMRA clubrooms, because I have got these details just right, mainly through trial-and-error. You can use your own radial arms and not use the ones made with the kit. Brass radial arms would be even better.

 The back-to-backs of the wheels need to be checked as well and this can be done using an NMRA track and wheel gauge which is an invaluable tool in the modeller’s kit bag.

I can and usually do bring my unpainted X class to our monthly meeting so you can see what I'm talking about. You can email me to remind me to bring it.   meanwhile I hope this helps you. 

Meanwhile, a couple of photos may help....... or not.