Blown gearcase seals can cause a lot of problems for your boat. If your entire gearcase gets filled up with water emulsified in gear oil, it’s on borrowed time. As such, you’ll want to catch degraded seals before that can happen and change them out for new ones.
Marine Tech’s Gearcase Pressure/Vacuum Tester will help you test for degraded seals before you take everything apart. Once you’ve determined the seals are the problem, you’ll need to change out the seals, remove any gunk or scale that has corroded the O-rings, and replace the O-rings as well.
Let’s get started!
Step 1: Remove the Upper Bearing Carrier Housing
Corroded O-rings can make it extremely difficult to remove the upper bearing carrier. To help you achieve the necessary amount of force without breaking anything, we’ve developed an upper bearing carrier puller that does the job easily and safely.
First, remove the 12mm bolts on the upper bearing carrier housing. Then, take your puller and work the claws down into place. Slowly pull the carrier housing out using the puller, and be careful not to drop it or scrape any polished surfaces.
Step 2: Pop the Shift Shaft Cover and Remove It
Tuck some clean, lint-free cloths into the area where the carrier housing was. That will keep any debris from falling in.
Next, gently pry up the shift shaft cover, working it loose a little at a time. Patience is key here — these covers are easy to break. As you remove the cover, try to keep it from knocking the shaft itself out of place so you don’t have to reset it.
Step 3: Remove the Carrier Housing Seals
Using a chisel, reach down inside the carrier housing to catch the bottom edge of the top seal and tap gently to work it loose. Try to avoid touching the sides of the bearing with your chisel, or you’ll end up having to replace that, too.
As the seal pushes out of the housing, dig out any buildup around the O-ring so it doesn’t fall down inside. Then keep chiseling gently away until the seal comes loose. Turn the housing upside-down and remove the seal. Then chisel out and remove the second seal in the same way.
Give your carrier housing a good rinse with some mineral spirits to make sure it’s nice and clean and has a totally smooth surface for the new seals.
Step 4: Install New Seals and O-rings
Now it’s time to install the new seals. Pay attention to the orientation of the seals so that you install them correctly. If you aren’t sure about the orientation, Yamaha has parts diagrams and schematics on their website that show you the orientation of almost every seal they make.
Put a very light coat of grease on the outside of each seal and press them into the housing one at a time. To make installing the new seals even easier, try using the end cap off a SeaStar hydraulic steering cylinder as a seal press.
Next, put the new O-ring onto the housing, taking care not to touch the razor-sharp edges. Add a tiny drop of grease to the outside of the O-ring so it won’t pinch anything while you’re reseating it.
Then, use a light coat of grease to press a new seal into the shift cover and add a new O-ring to its underside.
You’re almost ready to put everything back together, but first, coat the threads on all your bolts with just a little grease.
Tep 5: Put it All Back Together!
Make sure any shims or washers that came out of the gearcase when you pulled the housing out are put back inside the same way they came out. Then, slide the carrier housing back into the gearcase just until the O-ring rests on top. Use the puller again to tap it down gently, so the whole surface is even, and secure it with the bolts.
Once that’s finished, put on the protective seal cover and replace the shift seals and shift shaft cover, and bolt those down as well. And you’re done!
