1998 Mercury Force 40 Sheared Foward and Pinion Gear????

[malibu76]

Hey, Just had some bad luck, and my Forward gear and Pinion Gear are mangled. While in forward I heard a pop, immediatley cut it off. Disassembled and found the damage. I found the parts here on the site. My question is with these gears always running meshed together, how did this damage happen? There was noting else in the foot damaged. Whats the most common cause for sheared foward and pinion gears?

Thanks, Jimmy

[MercuryPartsUs]

The common reason is water in oil from a leaking seal. But it could have been shimming, bad bearing bad gear.

[malibu76]

The teeth that are not damaged show no sign of wear and the bearings are not pitted or worn.The oil was not milky and had no water come out when the drain plug was removed.The input shaft has a heavy spring which provides preload to the bearing above the pinion gear. Does this spring give any problems such as working up the shaft causing excessive motion on pinion and forward/reverse gear preload. Also the spacer that holds the bearings in place, which is all a part of the bearing, has pitted and damage to the top of it where the spring runs against it and holds down the top edge of the bearing. We have had a problem with the boat cavatating some especially when we get into some milfoil, and we have to put it in reverse to clear the prop and go again. But going into reverse and then in forward is nothing out of the ordinary so that shouldnt be a factor. We are however going to put a jackplate on it while its down to drop the motor so the foot will be deeper in the water. Is there any guide lines on where to mount the motor on the new jackplate? I dont believe I am going to get a electric adjustable one.

Thanks for all the info

Jimmy

[boats.net]

Sometimes there is no way of telling what caused it. Motor height useing a jack plate is trial and error, you will just have run it and make adjustments.