Yanmar SD31 manual - seal replacement

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jwdorst

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Yanmar SD31 manual sought (seal replacement necessary)

Does anyone know where to get a manual of the Yanmar SD31 sail drive unit? I would like to replace the seals of mine, and can't seem to find a manual or drawings anywhere. Does anyone have any comments on this job from personal experience?
 
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i recently did seals on sd50 - i dunno if that is similar as erm...i can't find a manual. You can usually get an exploded parts diagram from the dealers free of charge, and that's all i used.

Do you want to do upper seals (leak in engine compartment, which usually needs you to move the engine forwards) or lower leg seals (which needs the boat out of the water) ?
 
hm well looked at sd20 looks about the same as sd50 so lets guess the sd 31 is aboutthe same as well...

Marine Power will sell you the bits on internet and email an exploded part diagram. The parts diagram makes things look more complicated but never fear. I am guessing you want to do the much more common lower seals

get a digital camera to take pix as you go, everthing you take off, click a pic first.

Boat ashore

Drain the saildrive oil- Undo the lower drain and filler cap and leave it to drain while you do summink else like have lunch

UNdo the props and anodes etc until you get to two big cap screws/bolts (big Allen key heads one above the other) and undo these. You can see that these screws retain a half-inch thick bit of metal the seal housing. The seals you want to replace are all in this bit here.

Using a leather hammer or a ordinary hammer and bit of wood, tap this sideways so it turns 90degrees, and then you can get hold of the thing and tap it from behind and it comes off. If yer in a windy/dusty yard, tape a plastic bag over now-open saildrive to protect the geas etc.

The seals are some big o-rings on the outside of this housing, and also some other shaft oil seals - likely two facing each other - on the inside of this same housing you have just taken off. take pics.

You can bash out the inner (annular black rubber-type lip shaft seals) any old how as long as you don't damage the housing BUT there's possibishy some plastic spacers between the two seals and you shdn't damage them cos ned to re-use. I was ok using an old chisel first thru the other side tho, first one side then the other, you know.

The new shaft seals are a tight fit. They are easier to put in if the housing is warm cos the hole is fractionally larger, so put it on a hot home radiator overnight or in boiling water, and put the seals (in a bag) in the freezer overnight to makem fractionally smaller is the classic DIY way to do it.

Otherwise (in yard, no fridge or freezer) we found that one of the spacers from the assembly and a socket over was perfect - lightly tap in the seal nicely spread over the whole circumf of the seal THE RIGHT WAY UP (with two seals they normally face opposite directions, spacer betweenem), and then new o-rings go on the outside, light grease on everyhting so it's not dry and reassemble. Use thread sealant on the cap screws.
 
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To clarify. Bought the boat last year. No known maintenance history of SD. Now 15 years old. I'm the type of person that tries to stay ahead in the maintenance game, so (although no problems at the moment) I would like to replace the 2 seals that prevent water from entering the boat (the lower seal does that on its own of course, when all is well, and the upper serves as a backup).
 
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