no, you dont have to slpit cases to check. To check the counterbalancer bearing is remove your clutch side cover and you will see the counterbalancer and check the bearing play. Also take the stator cover off and the timing plate off and check that side too. Then from there you can check your waterpump. While you are in there check out the kick assembly for slipage and might be good to refresh the clutch while you are there.
Note that if you really want to do a big bore kit like the 330 you will have to split cases to have the cases bored. That would be a good excuse to go through the whole motor. Just all depends on what you time line and buget is.
Thanks for bring that trike back to life, looks like its going to be a sweet project
Tyler
85 ATC 250r -Under Construction
86 TRX250r
05 KFX400
02 400EX