Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 208Get this manual
8Hold pressu re up on drive shaftLightly turn drive shaft backandforth(No movement should be not iced at propeller shaft Dial indi cator registers amount of backlashwhich must be .019" to .027" (.483mm to .686mm) d Remove forward gear and forward gear bearing raceeRemove or add sufficient amount of shim(s) in front of forward gear bearing race to correct backlashNOTE: By adding or subtracting .001" (0.02Smshimthe backlash wi ll change approximate ly .0015(O.038m )
Reverse Gear
DETERMINING REVERSE GEAR BACKLASH Although reverse gear backlash is not adjustable, it may be checked as follows: 1Propeller shaft and bea ring carrrier must be completely assembled and installed in gea rcase 2In stall shift shaft in gearcase3Shi ft gearcase into reverse 4Slide6 in 1.5 in1.0(152.4mm 38.1mm) piece of PVC pipe over propelle shaft and position pipe against beari ng carrier5Secu re pipe against carrier with propeller nut and tab washeraThreaded Rod (Obtain Locally)WashersNutsDial Indicator Adaptor Kit (91 -83155)Dial Indicator (91-58222Al)Backlash Indicator Tool (91-53459)