BoatBanter.com - Johnson FD-12 lower unit leak

varnish_freak wrote:
I have a '54 Johnson FD-12 which I recently rebuilt pretty much from
the head down.
I've got it running and it seems to be doing just fine on the upper
end. But I've had to take the lower unit apart three times now because
I'm getting water in the gear case. I have replaced all the seals, the
impeller, and even the impeller housing but somehow there's still water
sneaking in.
Anyone out there have experience with old outboards of this vintage?
Any ideas on how I can stop the flood?
Your thoughts would be much appreciated.
Thanks much!

54???

The gearcase is not vented.

The power throughput vs gear/bearing sizes is very much under designed,
but they get away with it because the excessive heat generated can go
through the alloy case quickly into cold water.

There's a deliberate air pocket at the top of a not overfilled gearcase
to allow for this heat expansion.

The top (input) shaft seal might when new & on a new shaft be oil tight
but after only a little use they're certainly not air tight,
particularly so when trying to seal a completely unsupported small diam.
drive shaft thrashing around above, under power.

Once the air is expelled then the heat expansion has nowhere to go so
the leg builds excess internal pressure.

The seals are designed so as the pressure to be sealed increases so too
does the lip pressure against the shaft.

The lip seals quickly cut grooves in the S/S shafts (stainless is quite
soft).

As soon as the leg warms up it quickly squeezes the air out the top
seal, then when the engine is shutdown the leg quickly cools & contracts
allowing water to be sucked in to replace where the air bubble "was".

So a 54 leg has most likely got grooved/damaged shafts in way of the
seal surface. They can be "rebuilt" but this is not often good; as the
shaft, with no proper support between the engine & the gearcase, is only
"just" strong enough to start with.

So be careful paying too much to have it "repaired" because the fix
might not be long lived, indeed depending on how it's done the shaft
might not either:-).

Below is a paste of a previous post on how this is dealt with by
"some", it does work but is a fiddle to set up such that it's
"invisible" to the casual observer.

K

Paste:

I've noticed you're not getting any response, well watch what
happens when I answer!

I'm a bit bloodied & bruised at the moment & certainly not looking
for a fight with anyone, so if my response creates any flame or trouble
of any kind, (say a big dark e-male called Guido arrives in the night)
I'm really sorry so just ignore this, do whatever the dealers tell you,
pay whatever they ask. I should declare up front that I'm officially
band from responding to any OMC related posts, but hey.

Damn; Moe, Larry & Curly are going to go absolutely crazy about
this, I hope medical help is at hand.

(i) It is an old motor which you seem to have accepted is probably not
worth spending much money on particularly if the electric shift then
goes & dies. So before you give up on it, or maybe waste a lot of money
on it; consider this.

(ii) You say the seal under the water pump has gone & this might be
right, but the problem is that as the gearcase gets hot the expanded oil
has nowhere to go so pushes the air in the gearcase top past the seal,
which is no problem really until it cools again because it then sucks
water in. You can of course rebuild with new seals etc. but the real
problem is usually the shaft itself gets grooved & worn, so even a new
seal can't seat properly or if it does, not for long.

(iii) Your decision obviously, & because it's not in the manuals & costs
virtually nothing, very much frowned upon by the dealers, but we've had
some success with old similar problem motors by;

(a) Buy a SS short, hex headed set bolt to replace the top
filler screw (take the old filler screw with you, to get the thread
right, it's a surprisingly big thread on a small head; hangon... a
tick.... I've just gotta write that down)

(b) Get some small diameter copper tubing & placky tube to
tightly fit over it & a small container, we use a clear placky sauce
bottle.

(c) Drill a hole through the middle of the new bolt & silver
solder a short length of copper tube in, put another piece of copper
tube into the spout of the sauce bottle. (epoxy if needed)

(d) When you have reassembled the leg, it seems you have no
problem with that, just make sure all the electric shift wires are
routed/clamped as original, fill with the correct oil in the normal way,
but with two or even three of those ripoff priced little OMC nylon
washers, (or Silastic) put the ventilated new bolt in the top hole.

(e) Now mount the sauce bottle somewhere, they will fit under
the engine cowling if you want (drill a little hole in the base of the
engine cowling so the bottle's neck protrudes & will stay inverted) or
even inside the boat or engine well.

(f) Connect the two copper pipe ends with the placky hose,
attach the placky hose to the leg using cable ties, also use little ones
as hose clamps, fill the sauce bottle with the correct oil & very
important, put a fine (pin?) hole in what was the bottom of the sauce
bottle to let a little air in. (They forgot this with Curly & look what
happened)

Obviously now the gearcase has a constant oil supply at a modest
(less than 1 psi) positive pressure & as it gets hot it can expand, but
more importantly as it cools it sucks oil in instead of water. You can
see at an instant if the gearcase is actually losing oil, etc. & top it
up easily. Mercruiser sterndrives are set up this way.

This does no harm, costs nothing & can/has kept several old
gearcases that weren't worth reparing in service for several years. If
the oil level drops without the gearcase becoming hot followed by cold,
then the leak is really bad & you're not much worse off than before you
tried this

Placky = plastic.