Replacing The Upper Unit On The Gemini Stern Drive

I recently had to replace the upper unit of the drive leg due to a damaged pivot point in the casting. Because of the age of the Turtle, in doing so I was also upgraded to a newer design, which uses different bearings, and runs a little more quietly. Overall there really wasn’t much to this project, although I hit a few road blocks, because it was my first time taking the leg apart.


Most of the screws came out pretty easily, except one of the large ones attaching the upper unit to the lower unit, which needed to be heated with a torch to free. As you can see from the first photo, there aren’t that many parts involved, just the housing, 3 bearings, the shaft, the top gear, a large hex screw, and a large thick washer, referred to as a mudguard washer by Sillette.

This photo also shows the parts laid out in the order in which they get installed, and shows which way the roller bearing (the bearing to the far right in the second photo) should face when installed in the bottom of the casting.

Removing The Bearings

The third and forth photo show where the bearings get installed in the top and bottom of the casting. I got a lot of differing advice on how to install the bearings ranging from heating the casting with a torch to tapping them in. What I recommend and what I’ll do next time is freezing the bearings and installing them all at the same time.

Then put the leg out in the sun, on its side, so none of the bearings will fall out, and allow the bearings to heat up and expand back to their normal size. At this point they should be tightly in place, and the shaft should slide in easily. This way is a little more time consuming, but I think it’s the easiest way to do it, with the least chance of causing damage to any of the parts.


Once the shaft is in place (photo 6), the gear just slides on top and you reinstall the large washer and screw. At this point the upper unit gets screwed back onto the lower unit. On the joint between them, as well as the top cover, and front cover (where the CV joint is) I used a Locktite Gel Seal/Gasket Eliminator, comes in a large red tube. I’ll update this with the exact part number once I find it.

Apparently Locktite makes a lot of different sealers in large red tubes. I was given an almost used tube from one of the local outboard shops. The final step, before screwing the top cover back on is to put a 2×4 in the prop to hold it in place, and tighten the screw on the top gear, but not so much that the gear can’t be turned by hand.

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