Prop Crankshaft Seal Replacement
Completed 8/20/2011
This is one of those jobs that I wasn't hoping to have to do, but
yet I had to do something. I've had a couple of leaks
develop in the last year. One of them was the plug gasket
just behind the prop hub, for the governor shaft. It was no
big deal at all...just a simple one of those copper crush gaskets
that had finally become not-snug-enough...and I replaced it with a
fiber gasket with a part number from the parts manual. It
was causing a drip down the front gear leg when parked.
Then if you look at the nut in the middle top row photo below,
it's a thru the case bolt. It was either that nut or one
above it out of the picture that started leaking next. I
took the nut off and saw that there's no washer at all other than
the regular metal washer...I guess they don't call for them
either. Strange, but oil can leak out of there. So, I used
some anaerobic sealant and fixed that one. With that done, I
thought I was home free and would have no more oil drip mess on my
air box and lower cowl....well, close, but not done.
After all of the above, when I'd fly, I saw just a couple dozen of
the very very faintest oil streaks on the windscreen, only on the
right side. It was as if a tiny pinprick dot of oil had hit the
windshield and flowed upwards. Not enough that you notice it
on oil consumption. Not enough that it drips in the
cowl. Not enough that you can hardly even SEE it unless
you're in the right lighting....but it's there.
With nowhere left to turn for the time being, I figured it just
HAD to be the prop shaft seal. I'd replaced one before on a
different plane, so it wasn't totally foreign to me. On that plane
I had used a product in a small white can called Permatex 80017
Aviation Form-a-Gasket #3 sealant (supplied by my A&P working
with me at the time). This time around in my research I
found that the stuff to use is Pliobond
20, available at Aircraft Spruce among other places. It
provides a real fast setup time too.
So I headed out with my copy of Service
Instruction SI-1324c to the hangar and started work. I
pulled the prop, then had to pull my Lightspeed ignition pickup
ring, to get clear access to that area. You can see some
slight seepage along the case center line from the leak.
Funny thing is, my ring gear and associated parts were dry as can
be, with no oil on them. So, although it was leaking there
wasn't much getting flung around. The seal that popped out
was a split seal variety. I had obtained from Aerosport
(free) 2 new seals, both the split and solid round style. On
the old plane I did the solid seal. I decided to give that a
try again. Installing the seal is a bit like giving birth,
in the amount of stretching that seal takes! I removed the
spring, heated the seal in boiling water, greased the seal a
little, used some rounded edge non-sharp instruments and a pin to
hold the seal while I stretched it over the hub, and then
reinstalled the spring in the seal. After a bit of cleanup
to get rid of the oil/grease from lubing the seal, I was able to
apply the pliobon with q-tips and then stick the seal in the
bore. The job took maybe 4-5 hours I suppose. The old
seal, pictured below, had dozens of cracks around the inner lips
of the seal. It was easy to see that it had hardened
somewhat over time. That was the good part...I was glad to
see that the old seal was not perfect, because I didn't want to do
the job for nothing.
At present, I've put about 18 hours on since then and while the
oil up the windscreen isn't 100% gone, it seems to be drastically
reduced. In 4 hours I may get just a fraction of what I did
before, and even that was light. I'm still not sure if it's
licked, but there may be some additional oil trapped in nooks and
crannies that is still working it's way out. Prior to this
work, I was able to look at the cowl, just adjacent to the upper
inside corner of the right intake, and see that in the spinner gap
was where the oil was coming from. This seems to indicate
that it has to be from the prop area, one way or the other.
I'll be doing an oil change soon now and will give a good
inspection and if I note anything new I'll add it to this
write-up.
Oh, and while I had the prop off, there's a ton of grey sludge
that builds up in the inside of the crankshaft and prop hub...I
was able to once again clean all that out. It builds up
enough that it may be working checking every 500-1000 hours to
clean out.