removing saildrive

I'm trying to remove my saildrive to rebuild it over the winter. Something caused my zinc to corrode away completely over one season and the casing was damaged by corrosion. Maybe a grounding problem, I haven't figured that out yet.

I removed the four mounting bolts and also the two smaller bolts from underneath. The drive unit is free to wiggle around. I followed directions from khardy's post and was able to lift the engine up off the mounts, but it's not separating completely. It seems to be still connected somehow to the saildrive. When I lift the engine the rubber membrane (still bolted to the hull) is lifting and preventing the engine from moving further. Does anybody know what I'm missing?

Thanks Bill, your description was helpful. The problem that the "intermediate piece" (top ring of the saildrive above the membrane) was stuck to the bottom of the engine. Making sure everything was disconnected and whacking it with a rubber mallet freed it up.

You may be right that the prop lost its electrical isolation from the rest of the saildrive. The rubber lining looks to be intact but it's possible that the prop body was making contact with the screws that hold the zinc. If the zinc was inadvertently protecting the prop that would explain why it corroded away so fast.

I really, really want to make sure that this doesn't happen again, so I'm open to suggestions on other things to look for. I bought the boat out of the great lakes and put it in saltwater for the first time last year. I suppose it's possible that something was set up wrong for a long time but was never a problem in fresh water.

The internals of the saildrive, except for the outermost prop shaft bearing are ok. The bottom part of the housing has a dime-sized hole in it from corrosion. If I can't get it repaired (welded?) it's going to be expensive to replace.

--Andy

khardy's suggestion I believe is your best solution. I've seen many legs repaired nicely with epoxy... The key after all repairs are done is to recoat leg with 4-5 coats of interlux interprotect 2000 (my fav barrier coat)and be sure to check zinc frequently. There may be a bad ground at the dock?

Thanks guys, I'll try an epoxy repair. I wasn't aware of those McMaster products but they look perfectly suited to this.

I was thinking more about Bill's suggestion that the isolation between the inner core and outer body of the prop may have failed. I measured the resistivity between the outer body and the inner spline and got 1.3 kohm. I don't know what's "normal". If any of you have the inclination to test yours, it could be done with the prop mounted, measured between the outer body and the propshaft. I emailed AB Marine, the North American Gori distributor, and got this info:

"You do not say how old your propeller is. The Gori saildrive hub also has a
security cam system, which increases the longevity & ensures manoeuvability
at all times - a "get home factor" even if you strike something & the
bushing fails. Possibly this is touching due to breakdown of the bushing.
The hub can be revulcanised. It need to go back to the factory. Cost
$496.00 + freight."

Boat mooring areas have in recent years become bombarded with electrically charged water. Dock and 110/120V shore power and all sort of systems and equipment running discharge current into the water in most marinas, some worse than others. In other words, the problem may not be with your boat, but could be a leakage fault in a nearby boat, or just a combination of small leakages in big numbers from the multiple boats around you.

When in the water, I dangle a 1 kilo zinc over the side grounded to the exhaust manifold on the engine. I suspend it to a depth to get it as close to the s/d unit as possible. If you do this and it works correctly, you should notice deterioration to the portable anode and much less deterioration to the fixed anode. If I rely only on the fixed anode, it will require changing every few months. If the marina in which you keep your boat has conditions anything near what we have at the West Vancouver Yacht Club, and if you did not inspect or change that anode for a year, I believe you would definitely have a problem. It is a very small anode and part of its volume is made up of a ss backing plate, so the actual volume of zinc on it is tiny. I suggest you augment it in any case with a big chunk over the side.

I repaired the saildrive with G-flex from West System. Looks good but I haven't tested it yet. When reinstalling the saildrive, do I want to use any sealant on the upper and lower membranes? I think when I disassembled it there was something that looked like 3M 4200 on the sealing surface of the outer ring (where membrane contacts the hull), but nothing on the inner ring (where the membrane contacts the saildrive).

Thanks, Andy

Thanks to all of you for your advice in repairing my corroded saildrive. I have the boat back in the water and it seems to be working ok. However, I'm hearing a whining sound when cruising at high engine speed. It's only there when at more than 3/4 throttle. This sound wasn't there last year so I suspect it's something to do with my repair. In addition to fixing the saildrive casing I replaced the front shaft bearing/seal. The gears all looked fine. Any ideas as to what might be causing the whine?

thanks, Andy