I have the SD20s with 2GM20
engines on my 1996 Tobago
35. I have torn down the assembly to investigate and work on the diaphragms, although I did not replace them.
To do this in the Tobago
, I had to disconnect the saildrive from the engine, disconnect the engine mounts from the "plinthe", and slide the engine forward. I then removed the bolts that hold the saildrive to the plinthe, and disconnected the saildrive from the rear motormount.
The bolts that hold the saildrive down to the plinthe (That is what the manufacturer calls the fibreglass box that comes with the engine and saildrive that is glassed into the bottom of the boat and holds the complete assembly.) compress the edges of the main diaphragm and an "0" ring against the plinthe.
The saildrive, with prop removed and shaft protected with plastic and padding, can be carried out of the engine room by one person, but my wife certainly helped with steering
out of the Tobago. Once on the ground, after knocking the barnackles off the underside, the bolts that hold the main diaphragm come off reasonably easily. As I recall
, however, the same bolts hold the upper and lower assemblies together, with the diaphragm sandwiched in between. Therefore, reasonable cleanliness and tidiness should be followed.
diaphragm is held in place by two damned expensive, skinny, steel
straps. Likely the straps will rust at the welds before the diaphram lets go, and they could be damaged by the effort to take them off. If there are any special tools, it must be related to the installation
if the steel
bands. Good small needle-nose pliers, a sharp knife, patience, and ingenuity can get you by.
I was only in there to clean out salty water
that had got in between the diaphragms that set off the sensor and removed its value to us. I found the secondary seal was compromised, likely by me stepping on it during my oh-so-steep learning
curve with the boat. Since I couldn't get a new strap in time, I made one with a dremmel tool and a stainless steel strap (there is no room for the basic screw that normally tighten a strap).
I have no idea how old my diaphragms are, but they look great. I was told by somebody that these diaphragms should be replaced every 2 years, and that this should be followed, esp for a boat making long voyages. I went to La Marin in Martinique
to buy these for replacement, and the people who could have made hundreds selling them to me told me I was being an idiot for buying
them before there is a problem. They have them in stock and will get them to whatever boat yard I might end up in.
I decided, after being made to feel stupid (no worries, I'm used to that), that having 2 layers, with a sensor, and with the engine area in the Tobago behind a half-bulkhead, and the boat being considered unsinkable, that I would wait for a problem. We would have to lead more than two lives to know what is the right thing to do in most situations.
If you did decide to replace the two diaphragms, I would recommend replacing the steel straps at the same time. At least have them available. Yes, more expensive. How much time? I do not think one person could do it in under 2 hours, esp the first time, and a full day might be required. The bolts are all large, and shouldn't strip or cause trouble. I had trouble with the sensor, and it took me 2 days to clean out the broken, stuck plastic out of the threads with dental tools. Wouldn't it be fabulous if we could move every threaded object on our boat every 4 months or so?
Hope some of this helps.