I recently picked up a frame from a prewar 227. After cleaning off a lot of old grease I discovered that this locomotive had a custom made worm and worm wheel. These were very nicely made. The worm had a single lead and the worm wheel, the gear on the axle had 20 teeth. The stock worm is a three lead worm and the worm wheel has 21 teeth.
The srock 227 has a gear ratio of about 14.77 to 1. This means that the motor turns 14.77 times to make the wheels turn once. With the custom made single lead worm and gear, the gear ratio was about 42.2 to 1. This switcher was a really slow running locomotive.
In the photo below the gear on the left is the stock worm and gear and the worm and gear on the right is the custom made, single lead worm.
