Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 255Get this manual
Reverse Gear Backlash CHECKING Revers Gear Backlash0.040 into 0.060 in(1.0mm to 1.5mm)
Install dial indicator and align the dial indicator pointer so that it is perpendicular to and touching the "I" mark on the dial indicator toolnghten the indicator tool onto the drive shaft and rotate the drive shaft so that the needle in the dial makes at least one full revolution and comes to on the dial indicator scale
Although reverse gear backlash is not adjustable, it may be
checked as follows:
1Apply backward pressure on the propeller shaft as follows:
aInstall the pinion nut adaptor, washer and propeller nul as shown
aNuts (4) (obtain locally) Threaded Rod (318 in(9 .5 mm) obtain locally) Dial Indicator Holding Tool (91 -89897) Dial Indicator (9 1-58222Al )
e Indicator Pointer
I Backlash Indicator Tool (91-53459)