i hit a snag putting my B50 back together a while ago.i put the updated alpha bearing and carillo rod in it,and now the crank tightens up when i snug up the crankcase bolts.
as you B50 guys will know,there is a bearing spacer that goes on the drive side of the crank before it is offered into the case half.so the questions are,is (was) that spacer available in different thicknesses to allow proper endfloat with varying tolerances? i'm guessing the new bearing has slightly widen'd the crank,and my spacer is now too wide.
You need to have the faces on the side of the wheels where the bearing touches machined to give you back 3 to 5 thou end float. Before doing that however you need to ensure the new big end pin is seated correctly in the tapered holes in the flywheels. I would advise against thining the bearing spacer as this would move the whole crank to one side and the con-rod may not be central to the bore.
This seems like a common thing with Alpha Bearings. I have installed four Big ends to bikes over the last year and 1/2 and all of them have ended up like yours, so that should put your thoughts at ease regarding the growing big end.
on to making space.. have any spacers been placed between the main bearings and crank case? this is where I would start.... If not then I would start looking for another place to make space.. but as Kommando said in the preivous post, you need to make the space evenly between both sides so that the crank remains central.. 3 - 5 thou endplay should do it for the space.