I have a basket case Motor that I am working on. It has the right crankcase # 315 that the bearing end of the countershaft on the Right side is ruined> I've seen this several times unfortunately. Included in the basket is a brand new never used Right Crankcase that has 44401 stamped on it.
  The bearing hole is about 2 mm larger than the 315. 
  A friend told me there was a service Bulletin that addressed this...# 336?
  Anyway , 2 questions
  will the 44401 work...seems to match up perfectly
   what is the new bearing # that I would need to order.
  
        Thank you,

      mp

A CT3 should have come with the larger needle bearing... 23mm OD vs 22mm OD.   This change was made during the CT2.  Anyway, the revised 23mm OD bearing is 93311-31507-00 per the Service Bulletin. 

BUT!!!!  Yamaha used the same basic AT/CT architecture for the electric start DT125 in 1974.  (The 74 DT175 got a pretty much redesigned engine with the "jackshaft" shifter)

The Electric Start DT125 got an even *bigger* needle bearing in the right case.  25mm OD if I remember correctly.  The part number for it is 93311-31567-00.  My guess is this is what you need.  I'm pretty sure Yamaha kept the CT3 15mm shaft diameter for the 74 DT125 so you should be ok if the bearing OD you need is 25mm and the cases match up good.  

 

Ok… thanks.
  Measure the hole it’s 25 mm.
  Gives me a direction to go!
  Thanks again