Boat hypochondria or shaft coupling problem?

[ChessieSailor]

Hi all,

I'm known for both "boat hypochondria" (seeing problems where they don’t exist) and its opposite "boat denial" (refusing to see real issues), but yesterday I was adjusting my packing gland and spent some time examining my shaft coupling. It was replaced by a very good yard mechanic in 2009 using the old shaft (also relatively new). It has two seasons with low hours on it (boat out of the water last year). I noticed the small piece of shear key protruding from the keyway, but I can't say for sure whether or not it was installed like this or whether the key is working its way out. I can see how it is not sheared at all on top and also that the “groove” (not its boat name) on the shaft slopes up, which would prevent the key from working its way out depending on how long it is. I also noticed that the two parts of the aft flange are not completely flush on the 1'' shaft, but again, I can't say for sure if it was installed like this. I ran the boat at 1200 RPMs in gear against the lines and the coupling/shaft did not seem to wobble or vibrate excessively and alignment seems good (to my eye). So have a look at the photo and let me know if anything seems amiss.

 

[Don Crowther]

Looks good to my untrained eye!!

 

[Ralph Johnstone]

Simply shows that key is slightly longer than the depth of the coupling which is the way you want it.

 

[Dan Johnson]

I agree with Ralph. No apparent problem evident.

 

[Stu Jackson]

I had a shaft key work loose many years ago. Bought a new one and a spare, but put a plastic wire tie behind the key on the shaft. Still there.

 

[Ron McCoy]

Yours looks good. See how the shaft curve is cut (sloped if you will), the pin can't move any further out if it tried.
As for the alignment, the only way to be sure is to measure it. Yanmar likes .003" all around the coupling. Remove the coupling bolts (usually four each). Insert a feeler gauge at all four quadrants (top,bottom and left and right). Spin the coupling and test again. If one or more quadrants are out of tolerence, loosen the appropriate forward engine mounts and move the engine to align the engine to the shaft. This can be complicated for the neophyte and time consuming. If you're not sure, find a qualified marine tech to do the work. Have the engine in alignment with the shaft will save wear on your cutless bearing, transmission and possibly the engine itself. Good luck.