Well, actually I got the instructions for this from Vance who posted them way back. Since doing my own thrusters with those instructions, Greg Cottrell came over one evening and we did his with the Vance method as well.
1. Take the motor apart. You want the can with nothing else attached, because when you drill holes in it there'll be chips, which should not be allowed into coils or anywhere else.
2. The magnets are glued to the can, so you can't remove those. Drill two holes on opposite sides of the can, making sure you miss the magnets. Choose the hole location so that once the thruster is installed, one hole will be at the motor's highest point and the other at it's lowest.
3. Tap the holes and install threaded plastic elbows for 3/8" clear vinyl hose.
4. Clean up the chips and put the motor back together.
5. Connect about 6-8" of vinyl hose to the lower elbow. Use a funnel to fill the motor with oil through the hose until it flows out the top elbow.
6. Wrap the hose around the motor (mine loops once around the shaft) and connect to the top elbow. You want to do this trying to avoid air bubbles, which means you make the connection quickly with oil flowing -- a puddle on the floor is unavoidable.
The hose has two functions; it comes in handy for filling the motor, but more importantly it's compressible. A tiny bit of air is unavoidable (barring a bathtub full of oil to assemble the thruster submerged) so the flexibility of the hose keeps the seal from being squeezed by compression of that remaining bubble.
That's it for oil compensation. Each motor should take you about half an hour to do. The other question that comes up is what kind of oil to use. I've used Marvel Mystery Oil and this time I just refilled with WD-40.
Now as for sealing up the cables, that depends on whether the motor shaft is going through the hull or not. If it is not, as on my stern thruster, then you've not got any significant pressure differential across the cable seal. I've just got that one sealed with marine silicone around the cable jackets. But on the side thrusters it's a whole different matter. Look at Emile's project, he's got a photo showing really super workmanship on a trolling motor penetrator. What you want to do is connect a section of solid conductor inline with each cable, to prevent pressurized oil from wicking along the strands. You have to pot those solid conductors with epoxy inside the thruster shaft. The shaft should have a groove or thread on the inside to give the epoxy something to hold onto. The tricky bit is the lack of space. You have to keep those conductors apart so they don't short out, but also have to keep them from touching the shaft wall. As you can see Emile did it with a plastic insert that acts as a spacer. Be as generous as space affords with the cable diameter -- you don't want to pot a space heater that melts epoxy.
good luck,
Alec
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Hi Alec. Could you explain in more detail how you switched over to the oil compensation of your thrusters?
I remember the past thread and drilling a new hole in the thruster casing was made for the addition of the oil.
How is the existing hole with the wires sealed up?
I found some brass compression fittings at the hardware store that the threads on the Minnkota motors match, and the original supplier also had an aluminum fitting with a rubber compression grommett that screwed into the nipple where the wires exit the motor. What parts and methods have you got on yours?
Frank D.