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Old 06-27-2020, 10:16 AM
tenders tenders is offline
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Shaft centering cones

If your boat has adjustable engine mounts, how do you know where the engine should go after a replacement or rebuild to be ideally aligned with the strut and shaft tube?

You guess. You can’t see the strut from inside the boat, and you may or may not have a clear view of the shaft tube. If you have a vee drive, as I do, you have essentially no way of seeing the shaft position in the tube without parallax, and certainly no way of maintaining the shaft’s position in that tube while adjusting the engine to it.

That’s why you need a “centering cone” sized for your shaft. A centering cone is shaped like a small solid funnel with a shaft-sized hole bored down its center axis. You first slide the shaft into the boat from the outside through the strut and Cutless bearing, but without the shaft seal, key or coupling attached. From inside the boat you slide the centering cone down the shaft, pointy end first, and tap the taper lightly into the opening of the shaft tube. This perfectly centers the shaft in the shaft tube, holding it in place and allowing you to swing the engine mounts into proper approximate position.

Once the engine is in place with the output coupling in line with the shaft, you take off the centering cone and assemble the shaft seal, key, and coupling. Then you finish the fine pitch and yaw adjustments with the nuts and threads on the engine mounts.

A boatowner would only need the one centering cone for the boat’s shaft size. A mechanic would want a set to correspond to typical shaft sizes. The market would include 100% of Moyer replacement A4 engine customers as well as anybody else who has replaced an engine of any type.
Ideal material: hard rubber, like a hockey puck. In fact this might be fabricatable out of an actual hockey puck, as that thickness would be quite usable.
Possible materials: 3D printing plastic, nylon, wood, aluminum, steel.

My prototype material: plywood. See photo #1. I sanded the taper with the wood spinning in my drill press since I don’t have a lathe. It’s extremely crude...but it’s actually very useful. From this I learned that my engine has likely been 3/8” offset from my shaft’s natural position for the last 25 years. See photo #2.

Possible design improvements:
* fabricate them in halves that get zip-tied or otherwise strapped around the shaft so the coupling need not be removed to get the cone on and off the shaft.
* fabricate them in a slightly flexible material with a cutout, making them “C”-shaped, so they snap around the shaft and hold themselves in place, again avoiding the need to remove the coupling to install and uninstall the cone
* use a gradual taper (ie, a taller cone) to hold the cone more firmly into the tube - at some risk of increasing the size of the cone beyond what will fit in some installations
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Old 06-27-2020, 11:54 AM
Hawkeye54 Hawkeye54 is online now
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Smile Shaft centering cone -

Really a brilliant, yet simple solution ! I like it

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