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As most of you know, I had planned on attending the
South East Regional Fly in at Evergreen, Al this past weekend. Well, as
some of you suspect, I didn't make it. I had not mentioned anything before
this point as a gearbox problem developed and I wanted to give Tracy the change
to inspect it before all the spectulation got started on a possible cause.
I have approx 30 hours on the gear box at this point.
First, the problem was in the gearbox, BUT IT HAD
NOTHING TO DO WITH TRACY CROOKS EXCELLENT and WELL
DESIGNED GEAR BOX!!! I will repeat that - the problem had nothing
whatsoever to do with the gearbox design (or components or parts or assembly) -
I am waiting for the drive to get shipped back so I can put it on the aircraft
and fly to the Shady Bend flyin later this month. Now with that preamble
out of the way. Here is the story:
Well, as I was doing my preflight before my planned
departure for SERFI last Friday morning, I noticed that the
engine was a bit harder than normal to turnover by pulling the prop through
(something I always do as part of the preflight). But, it was a cold 39F
morning, so I initially just attributed the difficulty to that 50 weight oil
being sluggish. However, ANYTHING that is not as it normally is, gets my
suspicions aroused. That gut feeling has saved me more than once and I
have learned to listen to it.
I attempted to crank and immediately noticed
that not only was it much slower than normally, but what really got my attention
was the battery voltage dropping to 4-6 volts! That was an immediate clue
that plenty of starter current was flowing but it wasn't turning the engine as
it should. So I immediately stopped cranking and sat there trying to think
the problem through. Got out and play with the prop some more. It was plain hard
to turn - not just sluggish oil.
I though initially it might be the engine bearings,
but once I noticed that the normal 1/2" of free play at the tip of the prop was
gone (actually, it was there - just very hard to move) I suspected the gear
box. Well, took off the gear box and the engine turned over fine so it
wasn't an engine problem, but I couldn't budge the prop flange. So rather
than destroy any forensic evidence by taking it apart myself, I sent it back to
Tracy.
He just sent me an email detailing the cause.
It appears that some nickel plating (some of you may not be aware- but, I had
the aluminum casing of the gear box nickle coated for protection) had gotten
deposited on the inside of the bronze pressure bearing on the end the gearbox
nearest the prop. For whatever reason, the Nickle accidently deposited on
the bronze bearing by the plating process started flaking off and some got
deposited and smeared onto the inner surface of bronze oil pressure
bearing. Most of the flakes apparently pass through the gear box
without effect. However, the tolerance on the pressure bearing for the
prop shaft is pretty small .0015-.002. In any case, enough of the nickel
plating had gotten smeared on the bronze bearing surface to reduce the tolerance
to .0005 inch. That was what was causing the binding.
I had inspected the components after I had
them plated, but apparently failed to notice a bit on the prop end of the oil
pressure bearing, the plated nickle has a sort of gold tent to it which makes it
blend with the bronze pretty well (at least to my eyeball). In any case, as I
stated earlier, nothing to do with the gearbox per se, just my failure to detect
and remove the nickle plating where it did not belong. I really appreciate
Tracy taking the time to inspect and fix the problem just before his departure
for Copperstate - what a gent!
Tracy, said that because I caught it so soon, there
was no damage to the shaft at all and only a very small groove in the
bronze. He bored the bronze bearing sufficient to remove any nickel
plating and the small groove and will be shipping it back this week. So it
looks like I will get to fly to Shady Bend after all. Was not looking
forward to the drive.
So now you know the story. I had not
mentioned the gearbox problem, because I did not think it useful to
do so until Tracy had a chance to determine what the problem was. Clearly
neither one of us wanted to think of a design problem (particularly Tracy-I
imagine) and fortunately it was not. I had not even considered a possible
design problem as I knew that Tracy had over 400 hours on his and many others
were flying out there. It Just another one of those strange
happenings I seem to attract {:>) perhaps because I try different things
- sort of like Rusty {:>)
The lesson appears to be that if you do get the
gearbox plated, powder coated, painted or anodize, etc. to protect it from
corrosion. make certain to protect and/or clean off any deposit that gets where
it doesn't belong. Second if you encounter the unusual, don't proceed with
flight, I know - needless to say, but I'll say it anyhow, if you encounter
anything unusual on preflight - don't fly until you have resolved
it.
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