On the pinion bearings, I prefer to polish the journals on the pinion to get the fit I prefer; light enough that I can get the bearing on and off without damaging it. Light enough on the front bearing that it will go in and out with a light mallet. Then you're able to set it up with the bearings you're going to use. I find the bearing fit on new pinions to be all over the place depending on who made them. Some just need the coating polished off, others require more work for an acceptable fit. Tolerances seem to be all over the place on these parts these days.
Read it again. Don't make it a loose fit, just a medium or light press so you can get it apart without damaging the bearing. If you can get it apart or put it together by hand, you went too far, IMO. Front bearing can be lighter, sometimes they will go together by hand with all new parts. 1 or 2 thousandths make a difference in the pattern. I want to set it up with the parts I will be installing rather than have to fudge it. Tolerances on the parts are all over the place these days.
If you have a spare gear set that you carry to the track, it should already have been set up with the correct shims and bearing on the pinion ready to go.
When the pinion nut is tightened, the front race, spacer (or crush sleeve) and rear race and all pinched against the pinion head. You will burn the bearings up, weld everything together and twist the pinion in two before you turn a race on the shaft IF you didn't make it sloppy loose in the first place.
