Cat SX - Struggling to mesh pinion & spur

[Verde]

Ive just set up a used sx I bought, but Im struggling to fine tune the spacing between pinion and spur gear. It's either too loose or too tight and I can't find a simple way of adjusting it. I read an old thread regarding the same problem, but it didn't get to the bottom of how it was solved, despite changing lay shafts and bearings.

Any advice welcome.

Jason.