Suzuki RA410 Manual page 331

6A4-72 ENGINE MECHANICAL
Main Bearings
General information
Upper half of bearing (2) has oil groove (3) as shown in figure.
Install this half with oil groove to cylinder block (1).
Inspection
Check bearings for pitting, scratches, wear or damage.
If any malcondition is found, replace both upper and lower halves.
Never replace one half without replacing the other half.
Main bearing clearance
Check clearance by using gaging plastic (1) according to following
procedure.
1) Remove lower crankcase.
2) Clean bearings and main journals.
3) Place a piece of gaging plastic to full width of bearing (parallel
to crankshaft) on journal, avoiding oil hole.
4) Install lower crankcase as previously outlined in "Crankshaft
thrust play".
Lower crankcase MUST be torqued to specification in order to
assure proper reading of clearance.
NOTE:
Do not rotate crankshaft while gaging plastic is placed.