mercruiser leg ratio
 

hi do i only need to take the top with 4 bolts off the top of the leg to count the teeth on the gears

yes, just drian the lube down a little till you can see the gears, mark one tooth and count them, I can't remember the number of teeth verses the ratio, but it shouldn't be hard to find. If you have hte same number of teeth on both gears, its a 1.65. You should have a 1.83 ratio with the 3.7L engine