Adding the next idler gear messed things up though. It looks like the worm gear is slightly non-concentric on its shaft. The bearings have been opened up to give a little play, but adding the next gear took away thay play. So, some more careful opening up of the bearings eventually resulted in free running of the gears.
By now, the stub axles used by the idler shaft muffs were quite a loose fit, and kept dropping out. It was time to glue them in place. For the second shaft, with the hole drilled in it, this was a simple matter of applying some super glue into the hole on the end of a pin. The worm gear shaft is trickier, because there is no room for such a hole. I inserted a small piece of plastic rod to ensure the two stub axles can never meet in the middle. Then I tried adding some glue into the muff, putting it into position, then inserting the stub axles through the bearings. First I tried superglue, then I tried Uhu. No real success with either, except that I managed not to glue the muff to the chassis. However, the stub axles are now a tighter fit, and might stay put.
The rear wheels were fitted next. The muff had to be reamed out quite a lot, but still retaining a tight grip on the half axles. Everything was still nice and smooth. Adding the centre wheels locked the whole chassis up though. The gear was hitting the solder and folded tab of the spacer fitted above it. The solder, and some of the tab was carefully filed/chiselled away until there was clearance. The same was done for the front wheels, but eventually, on Friday 13th, all wheels were turning sweetly, and very slowly, under motor power.
The chassis had been blackened using a CD marker pen. It needs touching up after all the fettling, but it is a quick, easy way to do it.
