Originally uploaded by Phil_Parker.
The dock tank locomotive is well placed for weighting. The side tanks are nice big boxes which you could fill with lead or any other heavy material (uranium anyone ?). Sheet lead put in during assembly would probably be best but to allow the lightweight testing I decided to drill holes in the bottom and pour "liquid lead" in instead. This is followed by some glue to hold the tiny lead balls in place.
A word on glue - don't use PVA as it can cause the metal to swell. I've seen a 7mm scale GWR 0-4-2 with the smokebox blown apart because it had been liquid lead'd and PVA'd. I've used a cheapo "Liquid Nails" style glue. It is supplied in a tube with a nozzle - which gave me the size for my holes as I used this as a funnel for the lead before forcing the glue in.
Once the glue is in, the holes are covered with masking tape and the loco set the right way up. This should allow everything to dry in the right place. Tiny lead balls find all sort of ways to escape and I know from experience can bung up a model gearbox !