"they aren't very hard to
"they aren't very hard to change, ipeller and housing are mounted on the top of the lower unit. there is usually four bolts and sometimes a nut that hold lu on . somtimes the shifter linkage is the tricky part. i'm not familiar with the mercs, my older johnson i had to drop lower unit down a bit then there was a coupler for shift linkage. once you have it apart there's a steel or plastic cover that the shaft runs through. take the bolts off and cover comes off to expose impeller. then it's just a matter of sliding old one off and sliding new one on. be carefull not to lose the keyway or drivepin,you'll have one or the other. i then slide on new impeller then slide on housing, then turn the driveshaft while pushing down on housing, just make sure your twisting the right way, you can tell direction by looking at which way old impeller fins were facing, my teo motors both rotate clockwise.also while it's apart you want to check the housing for hot spots or scoring, i would recomend buying a complete impeller kit and doing them both. remember to lubricate the new impeller with some grease before installing to prevent a dry start. if your not sure manuals are around thirty bucks and have better instuctions and pics. or most shops will charge about an hour labor plus parts, most impeller kits are between 30-50 bucks. you can also search youtube there are a couple videos of guys changing impellers, good luck"