Just to give another view of the same project:
Two weeks ago I replaced my backing plates with fiberglass backing plates. I also replaced the thruhulls and rebuilt all of the valves. It was quite a job! A couple of tips:
I pounded out the keeper bolts on the valves and then disassembled the valve in the boat. I used a soft lumber 2X4" (cut down to fit) to place inside the valve body and use as a lever to spin them off of the thruhull.
I used one of those vibrating cutters (Harbor Freight) to remove the old backing plates and most of the 5200. I used a 5 in 1 tool (high tech putty knife) to remove a lot more of the 5200 and finally a bronze wire brush on my drill to get the rest off. I used 3M adhesive remover to help get everything clean.
With the old thruhulls in place I put my fiberglass backing plate in and spun the valve back onto the thruhull. I used a thick piece of paper to determine where any gaps were so I could grind down the back of the fiberglass backing plate to ensure that the inside and outside of the hull was square. There were lots of times up and down the ladder. When I got it reasonably square on the backing plates. I then 5200 the fiberglass backing plates to the hull and spun the valves down onto the thruhull.
Removing the thruhulls (now you are probably asking why do I need to remove the thruhulls? Good question. Unless the backing plate is exactly the same thickiness as the one you are taking out your handles are going to be in the wrong place. You have to mount the valve where you want it and then spin the thruhull into the valve from the outside - you definitely need a machine shop to cut down the new thruhulls to fit. My machine shop charged me $25 to cut down all of the thruhulls) To remove the old thruhulls I use an open / closed end wrench. I inserted the open end into the thruhull down to where the tits are and then put a screw driver in the open end and spun them out of the hull. It was easier than I expected. I then cleaned up the hole of any 5200. It came out quite easy.
I then cleaned, lapped, greased, and reassembled the valves. I bought new bronze carriage bolts to replace the ones that were holding the old valves in place. These are not cheap! I drilled out the keeper holes from the outside to the inside of the boat. I then mounted the valves with the carriage bolts. I had the new thruhull in place loosely when I did this step.
I then placed 5200 around the bottom inch of the thruhull (part toward the mushroom end). Work the 5200 in well so there is no wicking through the threads. I put liquid Teflon (NAPA) on the top of the thruhull threads. This was in case it was tempted to leak. I was careful not to get the tefelon on the fiberglass as I inserted it and then spun the thruhull onto the valve using my open / closed end wrench.
Cleaned up everything with Disolveit and repainted the thruhulls (except for the two big ones that are used for the cockpit scuppers. I plan on using these for grounding my SSB and I wanted them raw bronze.
The entire job took me about a week. I had a helper for the mounting of the valves and installing the new thruhulls.
A couple of notes. I had a heavy duty bucket without a handle that I used for a stool inside the engine compartment. It was a life saver. I used a wire brush on a grinder to clean up the old thruhulls. Don't use this on the inside of the valve housing or the cone or you can really mess up them. The lapping compound was from NAPA. I got the fiberglass backing plate from an old sailboat hull that was being cut up. They are cutting up a lot of old boats in Green Cover Springs Marina. If you need fiberglass they can sell you some. Ask for it in long boards so you can run it through a plainer. I used a belt sander and it took FOREVER to sand it down flat. I used a grinder with a cutting wheel to shape the fiberglass. It actually went quite fast. Remember to only tighten the valves a little. The grease does the work not the mechanical tightening.
I had another post on this subject. You might want to look it up to see if I had any other suggestions
