Shims in the Coupling ?

[DennisDW]

Hi All,
After discovering, thanks to Nigel Calder's books, my inability to align the shaft was a problem with the coupling out of true, it occured to me that a temporary fix might be a shim in the between the faces. The gap is very small, maybe .004".

Has anyone tried this or have any thoughts on it?

Of course I will have the coupling faced at the next haul out but until then...

Thanks for your consideration,
Dennis

[KestrelBuck]

No, absolutely do not try shims. Shims are appropriate in a static situation, but are a really bad idea in a dynamic application.
I see you are in St Pete, Florida. In early 2010 I had my engine and shaft realigned and the cutless bearing replaced by Progressive Boat Yard in St Pete. Afterward I brought the boat north: down the west coast of FL, then all the way up to Chesapeake Bay. Because the prevailing winds did not prevail and there were many deadlines I had to motor a large part of the trip. The work done by Progressive was rock solid.

[Play Actor]

Assuming your coupling is at least 4 inches in diameter, 0.004" is probably a tolerable error in the coupling. I've tried shimming couplings over the years without much success. If you're within 0.004" and still have significant vibration, you may have another problem. Have you tried rotating the two coupling halves relative to one another, 90 degrees at a time, to see if the gap moves? Have you checked to make sure that the two halves are concentric? It's possible to have the two faces parallel, or nearly so, and still have the shaft off center to the transmission coupling, or to have a bent shaft.

[DennisDW]

Hi,
Yes, I've spun the coupling 90 and 180 and the gap is consistent and moves with the shaft coupling. It is concentric. There is an internal alignment lip and there is no run out with a dial gauge. I had the shaft cut down last haul out for a Max Prop installation. As per their instructions I had the shaft and coupling checked for face error. It came back to me with no indication of metal removed so I assumed it was ok. That may have been a false assumption. Or perhaps when I torqued down the set screws it threw it off. That really shouldn't happen on an interference fit I don't think.

It's not a high power application. A 3GM30 in a 15 ton boat spinning an 1 1/4 shaft and a 16" wheel.
Thanks for the replies,
Dennis