A long time ago in a galaxy far, far away, I built a Wills N7 kit. The chassis was built using the etches for the kit, now sold by South East Finecast. The original chassis had the 'posh' hornblocks from Gibson (I think) which were the lost wax casting with a tiny springs pushing down on the bearing with a bolt through the top of the hornblock to locate the spring and set the ride height.

All of this worked fine until you took into account the sheer weight of the white metal body. The body casting ment that the bearings were always running on the ends of the bolts and frankly the springs would do nothing except perhaps help a wheel drop down into a dip in the track. The net result was a very 'hard' riding loco which tended to clack a bit, most probably because when I had jigged the chassis up with the coupling rods for a start the bearings would have been set in the middle of their travel and now they were right at the top of the travel. All it takes is for one horn guide to not be exactly verticle and you get a tight spot.

The result was a chassis that ran perfectly until you put the body on.

So eventually something had to be done and, with progress on the other locos finished and the work on the layout not being exactly transportable to a Friday evening meeting, out came the N7 for another look.

Clearly I needed a way to get more springing and to actually carry the loco's weight on the springs rather than as 'unsprung' weight. The thinking on springing seems to have moved in favour of 'continuous springy beams' CSB (the details are so involved that the CLAG website and Scalefour Society forum have pages and threads which can cure any level of insomlia). The simple theory seems to be to use handrail knobs to provide pivots for a continuous wire along each side of the chassis. Then use some mechanism to spring the moving bearing vertically from this wire, for example an etch from the back of the bearing or even another handrail knob drilled into the top of the bearing. The idea is that you can then thread a wire through the whole lot and it springs.

The clever bit is calculating were the pivots need to go and for this purpose there is a fiendish spreadsheet on the CLAG website. The idea is you put in the wheel centres of the axles and then adjust the pivot points relative to these axles until the spreadsheet calculates the weight on each axle to the the same. Obviously the spreadsheet produces a figure accurate to more divisions of millimetres than I can drill, but it gives you a good idea where to aim for!

Retrofitting onto the N7 was a bit difficult as I didn't want to have to take the wheels of the axles and requarter them etc. This meant that I really didn't want to have to either thread anything around the axle or apply heat the bearings which would probably make the wheels melt! In the end I decided to solder a long hand rail knob to a little 3mm square of brass and then thread the knob through the hole in the hornguide previously used by the height setting bolt. This arrangement is then threaded onto the CSB. Amazingly the result works and the loco is now much smoother as it moves along the track with all the weight of the white metal body 'sprung'. You can tell this is the case as there is still about 1mm deflection if you press down on the chimney where previously it was 'solid'. All this was made much easier as the chassis still had my original builders marks where I had marked up each bearing with the corresponding horn block. This meant that I knew I could get the bearing and wheels back in the same way around as they came out.

Hopefully the pictures will show you what I've been talking about. I've got a bit to do into terms of getting the loco finished still, it needs the brakes back on, a cab floor and backhead and some weathering as a way of hiding the somewhat iffy lining... And no this isn't going to the the N7 that lasted as station pilot at Liverpool St fully lined out with an immaculate paint finish.

David