[John Webb]

The X03 came before the X04, the latter was put into production in 1954 and went on for many years and many hundreds of thousands were made.

Regards,
John Webb

 

[John Webb]

The X03 was the first version of the motor which could be put in and taken out of the chassis without having to dismantle the chassis - made testing and replacement easier. (There's quite a bit about the motors in Pat Hammond's "History of Rovex, Volume 1 1950-1965.)

Regards,
John Webb

 

[John Webb]

The X03 featured on the 81B service sheet is a second version with a single-start worm to give a greater reduction than the X04 had - so yes, there was the X03 with two-start worm, the X04 with two-start worm and then the X03 with single-start worm.

Regards,
John Webb