Saildrive diaphrams

[tribune]

Hello,

Has anyone replaced the the inner and outer diaphrams on a SD20 drive? I'm looking for an estimate of time and complexity and if any special tools required. Can this be done with the engine in place also?

Thanks

[Euro Cruiser]

Tribune, I have not. But based on hearing a lot of discussion on this issue, my belief is that the answer is dependent not just on the engine but (even moreso) based on the boat in which the saildrive is installed. Mechanics tell me that a diaphram replacement requires the engine to be lifted, and that these saildrive-equpped engines can be shoehorned into a position where that is very difficult to accomplish. With peripherals removed, how high can you see your engine being lifted?

Is the builder still in business? If so, I'd start there. Does the boat have an Owner's Assn? If so, I'd poll other owners and follow up with the mechanic who's done this work, if possible...unless the owner is knowledgeable of what was involved.

Good luck to you on an interesting project.

Jack

[GordMay]

I believe that the 'SD20' Saildrive is a Yanmar product, intended for GM series engines.

[tribune]

Yes it is Yanmar. Mated to a 2GM20 and in a cat with lots of engine room space. Only have owners manuals at this time but will pick up or inquire on an overhaul manual.

[captjohn360]

hey trib i have a 95 athena and was wondering the same thing. i was planing to haulout in dec . and check them than also how do you know when to replace them i shure dont want to if i dont have to ....jt

[GordMay]

As with any flexible "rubber-like" product, look for cracking/crazing, embrittlement, discoloration, distortion, etc.

From the literature:
Its dual diaphragm virtually eliminates leakage's. The main diaphragm, made of a tough, resilient material is virtually crack-proof to resist damage from any knocks the prop or shaft may take. This tough membrane is backed up by an inner, highly flexible sub-diaphragm. Between these protective walls is an automatic sensor that sends a warning to the cockpit should there ever be any leakage through the main diaphragm.

Presumably, upon alarm, you still have a functioning inner diaphragm (unless it failed first).

[captjohn360]

so ...if it aint broke dont fix it....jt

[Sonosailor]

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.

The interior 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 and removal 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.

[tribune]

Sonosailer

Just what info I was hoping for. Sounds like my situation exactly. Missing the bands on the port side and a mix of congealed salt between the stbd rubbers. Port sensor has wires broken off and looks like the stbd sensor dissolved from below. No water comes out but wasn't sure what to expect. The diaphrams look real good from above and below. Maybe I'll just replace the sensors and the bands on both sides. Do you recall the price of the bands and if your workaround for the bands worked I'd like to hear how you did it.

Thanks,
Ron

[tribune]

Sonosailor- sorry, lousy spellr.

[Sonosailor]

Trouble with secondary diaphragm is that the most interior steel band has to be repaired first.

You might be able to get both bands on from inside the boat, but I could not because of tight space (small multihull). I also needed to have a go at the sensor threads after the sensor broke off during extraction. The bands were ~$200 CAN, and were not in stock, so I held off, thinking I might be able to use existing bands, and meet my target launch. I had already spent a fortune on replacing the sensor - unjustifiable cost for two SS prods through a hunk of threaded plastic that could dry out and fall to pieces.

After dismantling and cleaning salt out, I found the interior band was broken. The bands hold the rubber in place by compressing the rubber around the assembly. A raised section of the rubber locks into a groove in the saildrive to prevent slipping. The band compresses by a built-in lever system. The mechanic simply pushes the band together until the lever is flat, then bends a retaining clip closed around the lever portion.

I had acquired some very large stainless steel bands used for repairing sewer pipe, and hoped the screw mechanism would do the job. No room for the screw assembly between the saildrive and the flange, so I had to improvize further. The old band provided the appropriate final diameter, so I designed around that. I cut off the screw assembly, then cut the same end to create a narrow tongue that could fit through a "screw-thread-slot of the other end of the band, and bent it outwards at 90 degrees. After choosing the target screw thread slot, my wife and I devised ways of pulling the band around the assembly in opposite directions. After many tries, we had the rubber in place with the little tongue through the slot of the band, and bent it over. I am confident mine will hold.

We re-used the outer band with no problem, and reassembled. As the outer band is accessible and visible to you before you start, you might want to take a look at it. Gently remove the band to get an understanding of what you are dealing with, and consider just buying the bands if time and money are not a problem. The original product does work slick (the home-made strap was anything but slick), but again, price is unjustified.

Only unique tool was a Ryobi (you might better recognize "Dremmel") for cutting the stainless steel band. No need if you have the Yanmar bands. I think we used needle-nosed pliers and vice grips, but may have used other SS bands or wire as extenders during the final pulling- I forget, sorry. The primary bolts that hold the saildrive together are large metric allen bolts. Metric keys are required, and provide good purchase. the Ryobi brushes helped a bit to get the plastic sensor pieces out of the threads, but gentle prodding with a bent awl and some dental tools allowed cleaning and preserving of those fragile aluminum threads.

I asked a lot of questions on the yanmarhelp.com site, and accessing these might help you.

[tribune]

Thanks again Sonosailor. All good info. I'll take a look at the Yanmar site too. You mentioned that the sensors were very expensive also. More good news. I thought aircraft were bad. Haven't checked yet but I assume the sensors are just plain continuity switches. May be a way to improvise these. I'll won't be down on the boat till mid November so I'm trying to get all my ducks in a row now. Thanks again for your great description of this process.
Cheers,
Ron