Join Date: Jan 2012
Location: British Columbia
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Boil your coupling in a pan of water, and pack ice around the shaft for a half hour, before putting them together. That should make it easy. If you have heated it in place , you may have warped the shaft. Check that out before re-installing them. Put the coupling on the shaft and resurface the coupling in a lathe. Cutting the shaft key way can also warp it out of alignment.
Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"