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 looks almost exactly like my situation when I reached the 160
hour mark. I checked and could not find any mis-alignment. I then
rebuilt the input shaft with a new sun gear, reinstalled the drive, and
flew it for another 10 hours while I waited for a new RD-1 from Tracy. I
still have the Ross drive, if the sun gear is the same as yours, we
could trade sun gears. Or the whole drive for that matter. You would
have to accurately measure it to see if it's the same, knowing the
variations in different units from Ross.
I want to see you at Sun-n-Fun!
Have you checked end play in the E-shaft to verify the thrust bearings
are holding up? I forget whether you have a thrust bearing in the Ross.
I do not, and the engine thrust bearings showed wear after 160 hours.
Chuck Dunlap
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