Mark & Debbie Mueller
I have changed the valve on the aft head. My advice to any 54 owner needing to change the aft head valve is to sail to an Amel service center and pay them to change that valve.
Before you start be sure to flush a large quantity of water and water with Clorox through the tank allowing it to drain thoroughly.
The valve will normally have an overlay of fiberglass between the valve and the stub in the hull that should be removed before trying to unscrew the valve. I used a Dremel tool to slowly remove the fiberglass; use caution not to damage the threaded nipple that screws into the valve. Arno does not overstate the fact that you will get bruises and abrasions when doing this job.
In my case removing the valve required a standard pipe wrench to get the needed leverage. Due to the restricted space I unscrewed the valve from the stub in the boat allowing the hose barb to rotate in the hose then unscrewed the valve from the fitting in the hose. Even warming the hose with a heat gun to make it more pliable I was unable to remove it from the hose barb first. I then removed the hose barb. Assembly began by putting the valve on the stub first then assembling the hose barb and hose. Take a look at the space you have to figure out a plan. It would be advisable to have an assistant with you to hand you tools. In my case I left the head in place so I could lay on it and reach back into the cavity, in the front head it might be easier to remove it to have a little bit bigger area to work.
Take a look at this valve by Groco. The unique feature is the grease zerk that will allow you to periodically grease the ball to prevent sticking.
Brass Ring A54