I'm a page or week behind but C4 is the ball clearance not the fit in the case from what i remember. If you assemble it like that & even if the bearing is a good fit in the case ring i'd put money on that you'd feel up & down play 'like a worn bearing' but will be the insert moving. Had it on my YZ125E but think i got a new case free for that one as worked for the dealer. But happened again on my YZ125F & i did a bit of a dodgy job of drilling & tapping "threading' 1/4 whitworth grub screws in 4 places to secure it. Drilled it so half the hole was in the insert & half in the case so thread was in both & then locktited the screws in slightly countersunk & punched the case 'not the insert' just for added safety but locktited the screws & never moved. I made them quite a tight thread in too probably by using a shortened starting tap to get shallow threads down the end of the hole. Was only 45 years ago haha, just like yesterday.

Yes, C4 is the internal clearance, I have seen "standard internal clearance" bearings spin in the case, possibly because they are too tight? 

A simple spin is not the problem here and I don't think the C4 question was answered so hopefully the correct bearings will be installed.

C4 bearings in that fully round pocket is NOT correct.
C3's are made for crush as in horizontal split cases.

Nothing to do with main bearing wobbling in pocket designed for slight interference fit.

cliff

your pocket is puckered

only hope is another set of cases or shim pocket, which may not center it correctly.
in that case C4's may work

Thanks Mark. Yes standard clearance is too tight in the race once pressed onto the shaft & inner race is expanded plus outer race is squeezed. Yep it aint good, hence C4 or whatever they say on the mag side.

Yes Morley, C4 internal clearance is what Yamaha specified as correct for that bearing. 

Oh, and on the other side (clutch side) Yamaha specified C3 internal clearance. 

(Crank has a "slip fit" into the bearing on the clutch side so makes sense internal bearing clearance spec is different)

You can actualy feel the difference with the bearing in your hand when comparing C4 to standard bearing. Just the slightest movement which is reduced by squash & squeeze on mag side.
I said it long ago but in my stupid days [no not today] on my B33 i used to solder the bearing outer ring because it was loose in the left side case.
Was a common trick. But this time i made it too tight 'by far' in the case & when i ran it up, with no time to spare on race day, it squeeled loudly.
So bugger it i layed it over on the left to get lots of oil & gave it a valve bounce or two.
Job done & shut it up squeeling--. Message is--don't do what i do lol.
Pitty photography wasn't easy back then.
Crank cases bubbling & fizzing in a large bucket of boiling water & lots of caustic soda crystals. Big scum of stuff on top of the water.
Then 'oh', the bearing fall in now. Bugger.