Most weedies use ball bearings on the crank...A bearing engineer told me a ball bearing will take half its rated capacity as a thrust bearing....The load capacity of most bearings used in our gassers is about 3000 lbs, so they could take 1500 lbs thrust...
Some of the small McCulloch weedies had roller bearings, as do ALL the Quadra/US Engines 35/41/42 cc engines.. The Quadra/US Engines have a small bronze thrust washer to take up the thrust....Works fine.....
Not many chainsaws use roller bearings..The later procuction 5.8 Sachs Dolmar engines had a big roller bearing on the clutch side..A ball bearing was a direct replacement, so the airplane conversions got changed to the ball bearing....