Replacing the rear seal in the transmission

Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
If the rear oil seal in the transmission fails, oil will be spattered 360°around
the transmission coupling (the coupling to the propeller shaft) and the oil
level of the transmission will decrease to zero. This needs a solution before
the engine is used again.
My 2001 Tartan 3500, #131, has a 3GM30F Yanmar engine (the ‘F’ means
fresh water cooled with a heat exchanger using sea water as the exchange
medium). This has a KM2P, 1:2.62, in forward, ratio, Kanzaki transmission,
also made by Yanmar, as standard. The area we need to operate in is very
easy to access under the berth in the aft cabin.
Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
This seal fails because of poor alignment of the propeller shaft with the
transmission or overheating (no oil left). My situation was unknown, but I
suspected poor alignment causing a leaking (original) stuffing box which I
had sought to remedy with a PSS dripless seal. The old stuffing box had
indicated previous chronic leaking (that’s sea-water in) to me, and maybe
the transmission seal had already been damaged?
I recognized the oil seal damage when I lost oil and the transmission did not
immediately engage with the engine running. It turned out that my engine
was nowhere even close to being in alignment (1-1/2° too close to level!) (see
below). The Tartan yard that originally sold the boat is responsible for this
as it should have been part of her commissioning check out.
transmission housing
coupling
hose clamps
PSS seal
lock nut
rotor
oil seal
stern tube
output shaft
bellows
propeller shaft
carbon graphite flange
O ring
inside of hull
It is not a particularly difficult seal to replace and inexpensive ($5 from
Yanmar and $1 for the “O” ring). The limitation on easy, in-boat replacement
Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
is having enough room in the space between the output shaft of the
transmission and the propeller shaft coupling (rear) to slide the propeller
shaft back and remove the output shaft coupling (forward bit). You could
also worry about the torque wrench you should get into that space with a
30 mm socket on it to accurately torque the lock nut (the manual says 61.5
to 83.2 ft/lbs (10 +/- 1.5 kg-m)) on the output shaft, if you are so inclined. I
wasn’t.
You should think about seawater coming into the boat whichever type of
propeller shaft seal you have. The seal is below water level. Do not walk
away from the boat for a week or so looking for parts or daydreaming, as is
my wont, and leave this seal susceptible to leaking after the propeller is
nudged by your diver or an adventurous harbor seal. You will get some
water in when you are messing with it and this will be retained by the nondraining well under the engine. We pumped this well out with our manual
engine-oil-draining pump.
The first step is, as above, to ensure you have enough room to at least
remove the forward part of the coupling which measures 1-1/2”, 38 mm, long.
On my PSS seal (see diagram) I could move the stainless steel rotor
forward, along the propeller shaft, 1-3/4”, 44.5 mm, which indicated I could
then slide the shaft back the same distance whilst maintaining the integrity
of the seal. In fact the rubber bellows around the stern tube could also be
loosened and slid back about 3/4”, 19 mm, so giving me a total of 2-1/2”,
63.5 mm. The rotor had two set screws (which need replacing once you
loosen them) and the rotor is hard to slide on the shaft - mine needed to be
tapped with a hammer initially, before it became a bit easier to slide.
Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
•I marked the couplings together (with a Sharpie) so I could put them back
in the same orientation (I can’t think why this matters, I just read it in some
book).
•I undid the four bolts that hold them together, marked the shaft next to
the rotor and the rotor itself for re-alignment later (same caveat).
•I moved the rotor forward on the shaft and slid the shaft back, bit by bit,
until I gained the clearance I needed to get the forward part of the coupling
out.
•I increased this clearance by loosening the seal clamps on the stern tube
and sliding the bellows and shaft back before retightening the clamps.
The forward coupling is held onto the splined output shaft by a specific
30mm reverse-thread locknut, that, on Catcher, was barely finger tight(!).
This nut has a thin lip facing aft that tapers to an edge. This edge is
supposed to be bashed into
the threads to lock the nut
once you’ve torqued it down.
On the forward side the nut
has a circular recess next to
the shaft, as if to hold an
“O” ring, but it doesn’t.
However there is an “O” ring
forward of this nut, it just sits
around the output shaft.
Replace it too.
•The oil seal sits in the transmission housing and has to be pried out with a
screwdriver. Be careful not to scratch the surface the seal sits in on the
Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
housing, as this could cause any new seal to leak. Its a bit sticky, but with
patience (and the destruction of the old seal itself) it comes out.
transmission housing
for'd part
of coupling,
removed
hose clamps
loosened
bellows,
stern tube
squinched aft
rotor slid for'd
on shaft
oil seal
propeller shaft, moved aft
output shaft
PSS seal
aft part of
coupling
inside of hull
•Clean the surfaces with a rag and tap the
new seal in (flat closed surface of the seal
faces aft) with a wood block and a
hammer until it is flush (screwdriver as
punch through the bolt holes on the
coupling); see the picture on the right:
•Put a new “O” ring on the output shaft,
put the coupling back in place and the
reverse-thread nut and tighten it to about
70 ft/lbs (95 Nm). I used a plain wrench
and tugged hard on it because that is all
that would fit.
Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
•Using a rectangular metal punch/chisel and hammer, knock the locking lip
into the threads in just one place.
•Undo your rotor and slide it aft as you slide the shaft forward, same with
the bellows, until all is in the original position.
•Replace the rotor set screws, tighten well and tighten the bellows clamps.
•With the four coupling bolts back in place, but not at all tight, check that
the two couplings have an even gap between them all around. Use anything
metal that is of an even-thickness to evaluate this (a feeler gage if you have
it). If they do not have a completely even gap all around, your engine is not
in alignment with your propeller shaft and should be corrected using the
adjustable height fore or aft mounting bolts.
As mentioned above, my engine was way out of alignment. I undid the nuts
above the aft engine mounting plates until the lock washers beneath the
nuts were free, then I tightened down the supporting nuts under these
plates to allow the engine to drop. I measured the engine plate height from
the engine mount with a 6” (150 mm) steel ruler before I started and reduced
this height by my calculated 0.34”, 8.6 mm, before I re-checked the
coupling. After some back and forth I got the space between the two
coupling parts measuring the same all around. I then tightened down the
top nuts onto their lock washers as tight as I could. See picture below...
Replacing the rear seal in the transmission/reduction gear.
Aligning the Tartan 3500 engine with the propeller shaft.
I refilled my transmission with 0.3 liters of 30 SAE (that’s ‘weight’) Castrol
oil (the oil level is checked with the dipstick sitting on top of the threads,
not screwed in) and ran the engine, engaging forward and reverse gears a
few times. Then I re-checked the tightness of the coupling bolts and the
engine mounting plate top nuts and checked for any leaks in the dripless
seal or the transmission seal. Thank goodness - there were none. The next
day I checked the oil level again after the oil had settled and took a little bit
out with a plastic glue syringe with a bit of tubing on the end, to make it
correct.
©Philip Roberts, 2013, Palo Alto, California, USA.