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
The gear box was purchased when old man Lou Ross was still involved, but
don't know who actually built the box. I agree that a new gear box is in
order. Besides, I would have never felt comfortable putting a turbo on the
engine with that gear box. So, will see what kind of schedule I can get
from Tracy on one of his gear boxes. If he happens to have one laying
around, I think I could get it on in time for Sun & Fun.
Ed
Bad luck Ed. Sorry to hear that. I would love to have a look at it with
a dial indicator when it is mounted on a rotary table or a lathe.
Could you take it all apart and just ship me the main casting? I'll pay.
Do you have friends there with a lathe? Chuck it up with a center
in the aft main bearing race and see if those teeth are machined concentric
in the casting. While you have it apart you could check the ring
gear and input shaft bearing for runout.
Paul Lamar
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