Hi Donald,
Skyport has no "dog in the fight" of inactivity or poor maintenance. I
always recommend without hesitation or reservation the retrofit of the
cups for the "later" 0-rings. Frozen oleos are distinctly uncommon on
Ercoupes actively operated and properly maintained. It is always a
"new owner" that "discovers" the insufficiency of prior activity and/or
maintenance.
Just as there is a huge difference possible between "rebuilding" an
engine (factory overhaul vs. "field" overhaul, new limits components
vs. acceptable service limits components, etc.) the log book entry you
refer to tells you nothing. "Paper" annuals take place, and not
uncommonly. Until and unless you get one of those oleos apart, you
don't personally know that the cups described in the log were actually
installed.
I find it difficult to believe your frozen oleos were actually
disassembled three years ago and reassembled with the Skyport cups and
brake fluid. Have you tried to contact the mechanic signing off that
work? Mechanics that just "go through the motions" and are unfamiliar
with Ercoupes more often than not just squirt fluid into the cap as the
plane sits static on the floor or ramp without taking the time to see
that it hits the piston and comes right back out. "Well, it's full",
they incorrectly presume; and another year passes until someone who
knows or cares gets involved in the process.
Let's speculate. If they were refilled with hydraulic oil, the cups
would have failed and much of the oleo fluid would have exited. It is
not my understanding that hydraulic fluid absorbs water (like DOT 3
brake fluid). A cup so deteoriated would not "clean the surface" of
the piston or cylinder all around so as to freeze the oleo parts
together so solidly as you describe. Just how the oleos would have
frozen due to rusting with any hydraulic OIL present at all in the
ensuing three years is a mystery to me...a sequence of events unlikely
as described. How could water get in there and rust an oil covered
surface (absent a flood)?
Oleo pistons and cylinders have no taper or "choke". Accordingly, I
find it hard to believe that the accumulation of rust from moisture
absorbed by DOT 3 brake fluid would have dimensional effect between
annuals presuming a plane to be flown even once a month. To such
extent that it did, the process could not occur if non-hygroscopic DOT
5 Silicone brake fluid is used. That's likely as "legal" as a nitrile
cup ;<)
Incidentally, it's really a challenge to center the hole in the cup
properly (for those that order Wagner cups and "do it themselves"). An
off center hole can cause premature failure, I would
think...particularly if the cylinder were not properly honed before
cleaning and reassembly.
Regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
--
On Jun 13, 2010, at 10:04, Donald wrote:
At the risk of offending Skyport, which is not my intent, I feel I
should share some observations about the MLG upgrade with the brake
fluid and "rubber cups".
I notice in my aircraft history, about three years ago the MLG struts
were totally rebuilt, with new donuts and the Skyport rubber cup
upgrade. I recently removed them because they were stuck in the
compressed position, making them absolutely solid links. To my
surprise, several others quickly reported the same problem!
I have been trying to pull them apart with several mechanisms, with no
success as of now, in other words they are complete junk, I think I
will probably pull the ears off the piston before they break loose.
They have been soaking in several types of rust solvent!
The problem appears to be that the brake fluid cleans the surfaces and
then moisture in the air rusts them, and the first landing they stay
compressed. If I ever get them apart, I will share photos of what
happened.
I would suggest that if you have such strut upgrade, that at least
every annual you pull the bottom bolt and drop the bottom part down
enough to at least check for corrosion of the piston (and bore). This
is a very quick and simple procedure, and costs far less than a
replacement set of MLG sturts (if you can even find them). Of course,
you must not try to lubricate the surfaces with a petroleoum product
because of the incompatibility with brake fluid.
I had a spare set of struts with belleville spring washers I used on
mine, and I put new O rings and hydraulic fluid. If they leak, I will
go for a nitrile cup and stay with hydraulic fluid.
Comments welcome.
