On Thu, 21 Jul 2005 11:29:29 -0500, "Jim Burns"
wrote:

Well, after only putting 12 hours on our Aztec since our annual, we've got a
bad prop seal on our left prop. The prop shop is overbooked until OSH is
over, so we've got it scheduled to go in Aug. 3. (One side benefit is that
while the prop is gone we'll have time to put in our new side windows!

The prop has 985 hours since overhaul, 8 years ago, with a recommended TBO
of 2400 hours or 6 years.

It would be a good thing to get in there and take a peek. I've always
recommended a re-seal/look-see at 5 years (then 6 when they started
painting the inside of the hubs). Have personally seen too many
corroded "H" hubs.

What happened? Most likely we over greased it at annual and then last
Sunday in 98 degree heat, the pressures in the prop were high enough and the
grease was thin enough to leak past the weak seal. We knew the seals were
weak, as there was a slight amount of grease at the roots of the blades, but
now it's being flung out over 3/4 of the length of the blades.

Normally there shouldn't be even a slight amount.

A couple of interesting things that we've learned.

1) For aluminum hubs, Hartzell no longer recommends simply pulling one
grease zirt then pumping grease into the hub until it exits the open zirt
hole. Now they recommend to pull one zirt and pump grease until it either
begins to exit the open zirt hole or after adding a maximum of 1oz of fresh
grease, whichever comes first. It's still important to remove on zirt from
each side of the hub before adding grease to prevent pressure from building
in the hub.

That has been the "official" procedure for quite some time. Depending
on the utilization of the plane the prop is bolted to, you may truly
need to pump enuff grease to flush out the nasty stuff. Internal
corrosion in the bearing cavity (where the grease lives) is a big
problem with compact hub H's. Having the inside of the hub painted
helps but...

The trick is to add the grease s-l-o-w-l-y and not to use a pneumatic
powered grease gun. If the grease coming out doesn't look like the
grease going in, pump until it does.

Why? Our prop shop says that they've been getting at least 2-3 props per
month that are still under warranty that have been over-greased and the
seals have blown. They say that they've been complaining to Hartzell about
the old greasing procedure for years, and they've finally addressed it.

I know it was in the "book" 5+ years ago (had a sister company across
the ramp that was a prop shop). People have been popping grease seals
for years and years, and will continue to do so.

The bearing cavity for each blade should be full of clean grease. A
new or overhauled H propeller requires topping off with grease after
it's placed into service. Especially if you are going to dy-bal.

2) Another thing that we learned is about Hartzell's recommendation to use
Aeroshell #6 grease. Our guys say that in warmer temperatures, it's simply
too thin, they absolutely cuss at it. For most GA piston engine airplanes,
our shop says they normally use Aeroshell #5 even though it's prohibited
from use at temperatures below -41F (placarding required). Hartzell uses #6
because it is a more "general purpose" grease, has a broader temperature
spectrum, and without knowing specifically the area their props will
operate, they feel it covers the most bases. I don't know about you, but we
rarely fly in temps below -41.

Remember the switch to #6 quite well, had #5 aircraft in the fleet as
well as #6, was hard to keep track (even with the little sticker).
Never had an issue with #6 being "too thin".

The shop we're using, Maxwell Aircraft, has been in the propeller business
since the 1940's, so they should have enough experience to know what they're
talking about.

I don't know squat about overhauling propellers, but I've allegedly
maintained a bunch of them (on personal and "working" aircraft). I
learned a lot more about what works and what doesn't periodic
maintenance-wise when the old boss bought the prop shop. A good
guesstimate would be that I averaged greasing a pair of compact hub
H's a week for 15 years. That isn't counting steel hubs, just
compacts.

Any comments or experience is greatly appreciated.

BTW, on the 135 aircraft, we cycled H props through mandatory overhaul
about every 2-3 years (before they stretched the TBO from 2000 hrs).
I've been out of the business for awhile, am assuming that they still
roll some types of blades during o-haul. It's a real bitch when you've
got a set of blades that meet/exceed every spec but are under the min.
diameter because rolling (and polishing to remove the roll marks) put
them under the min.

All these props (first with #5, then with #6) had nasty grease pumped
out of 'em-and fresh grease pumped in every 100 hrs (usually 6-8
weeks). Never had corrosion issues, had very very very very few grease
leaks at the hub. Did have a zerk ball stick very now and then-makes a
mess.

Regards;

TC