Here is some info on a recent Gen 2 gearbox failure (
See answers below
--- In firstname.lastname@example.org
, "Larry" <simpsonl@...> wrote:
> Could you provide a few more details about your failure? I do not
> recall seeing it mentioned on the group before. Appearance of your
> oil at change?
-------- The oil at the time of failur had 36 hours (mobile 1 75W-90
synthetic)The oil color was light and no observable particles in the
Any other warning signs before the failure? Noise?
-------- My Gen II Gearbox temps always ran hotter than the engine
and the oil temps. (Normal temps for me were 205 - 210F with climbing
temps for any power above 2100 rpm) In retrospect I have learned
that this was probably a warning sign. After the failure, I used a
loaner gearbox to get the plane home and it ran significanlty cooler
(15-20F)than my original gearbox so I speculate that there was
something amiss with my original gearbox. The day of the failure, it
was very hot in Atlanta and my GB temps were running about 215, this
was probably another warning sign that I did not notice.
> Spiking temps? How catastrophic was the failure? Did it occur in
-------- Failure was in flight, After cruising for about 1 1/2 hours
on the day of failure. There was a sudden appearance of loud
squealing noise and the gearbox failed about 3 minutes later. (gears
stripped and engine raced, I shut the engine down in flight) Pure
speculation on my part is that one of the bearings failed and after
the bearing siezed, it lead to a failure of the gears. Again, in
retrospect, I think the high temps were telling me about a problem
that I did not recognize. The dramatic difference in the loaner
Gearbox (much cooler temps) tells me that this was an issue
associated with my gearbox that may or may not be present in other
units. The new Gen III gearbox is much much cooler running in my
> I am also running a Gen 2 (blue front) PSRU and it typically runs
> the 200-210F range at full throttle and any prop setting above 2000
> RPM. My engine temps are usually about 30 degrees lower. I have a
> inch blast tube and a 1.25 inch blast tube to the bottom and left
> sides of the unit respectively. Aircraft Spruce delivered another
> inch tube and some scat today which will be installed next week for
> the right side.
> At 25 hours TT and 10 hours since the previous change, the Mobil 1
> 75W-90 oil looked slightly gray but there were no visible metal
> flakes on the fine screen that I strained the oil through. I am
> letting the oil "settle" for 48 hours and then will see if there is
> any sediment and if so, if it is magnetic. Then I will send to for
> I am upgrading to the Gen 3 in January, but am concerned that I may
> need to curtail my flying until then.
> Thanks for your information.
> --- In email@example.com
, "n62km" <n62km@> wrote:
> > David, I did have a complete gearbox failure on my H6 normally
> > aspirated Gen II gearbox after about 100 hours. It appears my
> > particular unit was behaving differently than most units (running
> > so it might not have be a representative sample of most units in
> > field.
> > I have sinced moved to Gen III and have about ten hours on it.
> > unit is running much cooler.
> > Steve RV8 H6