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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
Ed Anderson
Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com
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