1983 Yamaha 30EN Outboards Service Manual, Page 110Get this manual
GEAR SHIM ADJUSTMENT Before making shim adjustment, all parts should be thoroughly cleaned and blown with compressed airShim adjustments shou Id be made with the water pump removed Gear backlash
"A" clearance (called "backlash") is allowed
between the two mating gears in order to take into account possible errors in machining, center-to-center distance tolerance, deformation due to load or thermal expansion and oil film thicknessShim adjustments are required if the following parts are replaced