Regearing a servo

Hi everyone,

I’m trying to create a gear box for a prototype I’m building at home and need to re-gear a hobby servo:

to work with a better motor (I’m replacing its small pager motor that lasts 100 hours with a motor that lasts 1000 hours).

The new motor runs at about half the speed but twice the torque. Therefore, I need to reduce the current gear train’s ratio of 650:1 to 325:1

Any ideas on how to tackle this? I’ve never worked with these little gears before… I found out that removing the last gear from the train reduces it too much, to 125:1, so I may need a custom gear train. Any suggestions on how to do this myself or who to go to to get this made?