Ed Anderson wrote:
Well, got to the point in my conditional inspection of taking off
the Ross
PSRU (2.17:1) and inspecting it. I had planned on replacing the oil
seal as
this one had around 100 hours on it. I also wanted to check for any
wear of
the planetary gear housing spokes where they rest in the matching
notch
milled into the rear of the gear case. That is the area where Tracy
encounter wear after extended used.
The good news: No apparent wear in that area (Panetary in
Housing.jpg)
Now the bad news:
Upon removing and inspecting the gearbox, I discovered that the
front 3/4
axial length of each tooth of the Sun gear was gauled/galled? at a
depth of
roughly 1/4-1/3 of the gear tooth down from the peak of the tooth.
The
gauling pattern was uneven in that it looked like a series of pits
of
various size along the length of the tooth all connected together.
They
were deep enough to catch your finger nail on. The photo tends to
exaggerate
the pitting, but it was there on every tooth. (Galled Sun Gear.jpg)
I next inspected the planetary gears and they initially looked OK,
until on
closer inspection I found similar (but not as sever) pitting on one
of the
pinion gears. The rest looked OK.
It was clear from the wear on the Sun gear that only approx. 3/4 of
the gear
was engaging the pinion gears when operating. While the sun gear
could go
far enough forward to engage the pinion gears completely, it appears
that
the thrust force kept the Sun gear backed out of a complete union
with the
planetary gears. (Sun Planetary Mesh.jpg) Don't know if this could
have had
any bearing on the galling problem or not.
>From what I understand about gears (which is not much) this galling
pattern
is indicative of lack of lubrication or possible misalignment. I
had
measured the oil flow through the gear box at 2000 rpm and had a
pint/minute - similar to what others had reported. The total flow
would seem
adequate, but of course, it may not have been getting adquately to
all the
gear teeth. I am now wondering whether my extra drain near the
rear of the
housing which stopped the real seal leak may have deprived the Sun
gear of
essential lubrication or whether the lack of a thrust bearing
contributed.
In any case, no way to tell if I could get another 100 hours or 10
hours on
the gearbox, so I'm grounded until I reach a decision about what to
do.
Alternatives appear to be.
1. Acquire new input sun gear shaft (or replace the sun drive gear
on the
input shaft) and planetary gear.. Add additional lubrication
channel to
rear of gear box. However, I don't know of any source
to get a new/replace the Sun gear.
2. Purchase a redrive from Tracy Crook (my initial inclination).
Just wanted to pass on to the group, what I had found. Now the race
is on
to see whether I can get flying again in time for Sun & Fun (and of
course,
it would be a week or so earlier this years).
So if any of you "Gear" gearheads would comment on potential causes
for this
problem, I would appreciate it.
Best Regards
Ed Anderson
Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com
Looks like a classic case of severe misalignment. When was that box
bought
Ed? Too bad Chris Ross dropped the ball on the later boxes. Some early
boxes are still going strong in gyro's and other applications.
Examine the tooth slots in the housing and see if one side is worn
more than the other. Only one pinion gear worn is an indication of
that.
Looks like a severe case of non concentricity. In the old days, with
a manual milling machine, it is quite easy to make that mistake.
Now a-days with NC mills things like that rarely happen.
This would be hard to fix without a new casting.
I would junk it or sell it to someone with a machine shop.
Paul Lamar
Ed that sun gear looks like it was oil starved. Overheated somewhat.
Royce
In hindsight, Royce, I am inclinded to believe that inadequate lubrication
was a major factor. In my endevaors to eliminate the oil leak around the
rear shaft I did two things.
1. I reduced the diameter of the oil restrictor from the engine reducing
overall oil flow to the gear box.
2. I installed an additional drain near the rear of the gear housing.
While 1 and 2 solved my oil leak problem it may well have fostered the gear
problem. Althought it may have been a problem that would have surfaced
eventually in any case. Tracy Crook informed me that his Sun gear looked
like that after 600 hours. I had 256 hours on mine. But, over the past
year, I have flow the aircraft more and over longer distances. So heat
build up due to inadequate lubrication could have been a factor as well.
It may be that the lubrication path in the Ross design I have is simply not
up to the challenge. I believe that a couple of folks have added additional
lubrication, so it will be interesting to see if they ever develop this
problem.
Sigh! Well, this is what experimenting is about, finding out what works and
what does not.
Ed
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