Paul,
There are two methods in common use for applying the Teflon coating to a
cylindrical substrate. An older method involves a spiral or helical
wrap of Teflon ribbon. When the wrap is complete, the adjoining edges
of ribbon are fused someway to form a continuous covering. If one
examines a variety of Teflon insulated wire samples some will clearly
show this helical wrap pattern in the insulation. A newer method that
is more difficult and more costly involves extruding the Teflon onto the
surface of the substrate to form a continuous and seamless coating.
The cracks that are apparent in these two photos that Brian posted seem
to indicate a helical pattern. Rotary Aviation could have received a
batch of defective O-ring material or received the wrong material
(wrapped instead of extruded). It may be worthwhile to destructively
test some samples of TES O-ring material to see if cracks similar to
those shown in Brian's photos can be produced.
Aubrey Thompson
In the case of Creavey I think the Teflon is extruded first and the
silicone
is
injected in the liquid state. This is probably done in a mold so the
pressure
required to inject the silicone does not expand the Teflon. I could be
wrong.
On the other hand I think air may be required to convert liquid silicone
to
the rubber state. That is why they call it RTV or Room Temperature
Vulcanizing
I think.
These picture you attached look like very poor workmanship was used to
make
these O-rings.
I have never seen a TES O-ring that looked anywhere near that bad
including
the
ones we bought from McMaster car. Creavey quality control on the other
hand
is
excellent. It is on the cool side of the engine as well. The O-rings look
to
be the proper cross section size however. Perhaps they were well under
diameter
and somebody stretched them to fit. If you try to do this one section of
the Teflon will yield while the rest of it remains the same. Perhaps this
is what happened some where along the line.
I have always thought of rubber, and that includes silicone, as being
"compressible".
What has been brought home to me after reading some bad O-ring experiences
years ago
is; rubber is no more "compressible" than hydraulic fluid. Furthermore
silicone expands
greatly when heated. If it is contained in a closed chamber without
expansion room such as an
O-ring slot it will generate tremendous forces. Enough to crack cast iron
and bend steel.
Therefore it is extremely important to have the right section diameter
when
installing
O-rings.
If the O-ring is oversize for the slot the process of tightening down the
tension
bolts will cause the hydraulic force of the rubber to break the cast iron
end housings.
The problem will compound itself when the engine is warmed up to operating
temperature
as the silicone expands.
The last picture is what happens when the TES O-ring is too large in
section
diameter for the size of the slot. You can see that the Teflon was cold
extruded
into the space between housings prior to final torquing of the tension
bolts.
The date on this photo is March 2003.
Paul Lamar ...No rotor no motor.
Now I'm getting very concerned! I've installed these o rings in my 20B and
now I'm wondering if I should tear it down and replace them with factory o
rings. I'm getting very close to my engine installation and would rather
do
it now than after the installation. Do we know of success stories with
these
o rings? Or should I just change them...
Bob Mears
Supermarine Spitfire
Bob,
I installed Creavy TES o-rings about 4-5 years ago. While I've only got
about 25 hours on the engine, there is no sign of leakage to date. We'll
see how things develop. Where did you get your TES o-rings?
Mark St.
I got the entire overhaul kit from Tracy since he had a 20B kit. I would
have had to bought 2 13B kits from Mazda to get the everything I needed. I
actually assumed He had actual Mazda kits. I had no Idea there were any
other options out there. Plus I figured he was the expert on Mazda/Aircraft
since he does practice what he preaches. He's logged more hours in
Mazda/Aircraft than anyone else I can find, and he runs what he sells.
Bob Mears
I don't think he has Teflon O-rings in any of his engines. I know
he did not have them in the first two engines.
The RX8 engine he is now flying was built around 2004 and at that time
I don't think he or Bruce Turrentine were fans of TES O-rings. Bruce built
his
last two engines. I know his kit was not available at the time his RX8
engine
was built. I doubt seriously he has HIS apex seals or HIS Teflon O-rings in
his current engine. So much for marketing slogans.
Paul Lamar ...No rotor no motor.
I rebuilt a 13B engine over 7 years ago using teflon water rings, and teflon
oil control rings, (and even used them in the oil pedestal). They were
available even then from racing outfits.....I still have some I haven't
used......don't remember where I got them but they have been available for
years.....
Marc Wiese
Hayes Rotary Engineering sold them awhile back.
Paul Lamar ...No rotor no motor.
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