I also have replaced the keel bolts. I originally did it(1983) from the top, during the winter one at a time. I also took 4"x4"x1/4" steel plates and used them as washers to spread the load. Based on a slow leak around a keel bolt and small movement of the keel, I decided to drop the keel. In 1996 I dropped the keel, cleaned the keel top and keel sump, replaced the bolts(3 were bent), and reseated the keel. The keel had pulled down a little so it was wiggling in it's sump. I cleaned all the bolt holes and heated them for about a week to dry them. I then coated the top of the keel with Gougeon's epoxy(use this or another high solids epoxy that won't shrink on curing) thickened with silica and milled glass fibers. As the hull was seated on the keel, the epoxy came up thru the holes. I used even bigger steel plates over the bolts this time and let it cure. The epoxy coming out the bottom was faired into the joint seam. Its smooth, water-tite, and it doesn't move.
The bolts are 1/2" machine studs. I had them turned by my stainless guy. Very cheap. I had 3 extra made. Good thing too. I used stainless nuts also, not a good idea. 3 of them galled and destroyed the studs. Next time(There won't be a next time for me. The repair will outlast me.) I'll use bronze nuts, they won't gall. An explanation for those that don't know what galling is. In this instance it is the nut creating heat and welding itself to the stud as it is tightened under pressure.
There was some discussion that the keels were epoxied to the boat originally. Don't count on it. Many are not. In 69 and 70 they used something like 5200 to seat the keel. There was no epoxy in there. Later they used epoxy to seat the keel, and faired the joint better.
These keels had lots of voids and hollows as a result of the casting process. The factory did extensive fairing of them as part of the assembly process.
Blair Arden OTIS B. DRIFTWOOD Sail # 570 Columbia 26 Mk2
EMAIL: sailor570@compuserve.com