RE: CRRC 40cc kit
If there isnt too much clearance in bearing seat, you can fix it in place by red (nut-locking) high temp loc-tite.
If a bearing change is needed, you can dismantle it easily by heating the crankcase over 300-350 *C.
Once I even used a blue loc-tite (medium strength) and it still holds nicely after 20 liters of gas in a 26cc..