Rotary Engine wrote:
Don't buy after market apex seals! Stick with stock Mazda
iron apex seals or Iannetti ceramic apex seals.
We are seeing things on the rotor housing chrome wear surface
we should not be seeing on an engine that has only a few
hours on it.
http://www.rotaryeng.net/history.txt
I am not going to name names yet.
Paul Lamar ...No rotor no motor.
Paul,
Before seeing the chatter mark damage on Chuck Dunlap's and Dave
Leonard's rotor housings I wasn't convinced that ceramic seals were
worth the expense unless the engine was to be turbo boosted
significantly. I think I am changing my opinion.
I found this thread
(
http://www.rx7club.com/printthread.php?t=182522&page=1&pp=15) that
describes some torture testing of the ceramic seals made by NRS Rotor
Sports. It's worth a quick read of the 11 pages of the thread for
the detonation damage pictures and discussion. On page 4 of the thread
there are some links to earlier videos of the X-Treme Rotaries 20B
powered ski boat. It was originally fitted with different ceramic
seals on each rotor as a test. But, now it appears that they have
settled on the NRS one piece seals for all three rotors.
(
www.xtremerotaries.com/main2/Quicksilver/Quicksilver%20article.pdf)
There are several concepts mentioned that are probably worthy of further
discussion:
1) The price of the NRS seals in quantities of 5 sets is reasonable,
around $650. (group purchase, perhaps?)
2) When the ceramic seals have broken from detonation abuse, they
apparently are likely to cause less ancillary damage to other engine
parts than broken metal seals.
3) Wear on the ceramic seals
_and_ on other engine parts is much less
with ceramic than with metal seals.
4) The wear on certain springs used under ceramic seals has been extreme.
5) There is no mention of chatter marks in any of these discussions!
6) Most of the use of ceramic seals has been by the drag race
community. There is not much data on how ceramic seals act under
extended use in an aviation type duty cycle.
After thinking about the metal seals and the chatter marks for a while
now, here are some thoughts I'll offer for discussion. From the
photos, the chatter marks appear to have a wavelength of about 1/8
inch. At around 6000RPM the rotors will be turning at 2000RPM. If the
housing has a circumference of around 30 inches, then the seal velocity
along the housing is about (2000/min)(30 in) = 60000in/min =
1000in/sec. If 8 chatter marks per inch are showing in the housings,
the chatter frequency must be around 8000/sec. So, I think the chatter
is a squeak of about 8000hz. A squeak occurs between objects sliding
against each other because the static coefficient of friction is
greater than the moving coefficient of friction, so, the objects
repeatedly stick and then move. This is the mechanism that excites
vibrations in a violin string when it is bowed. I can't think of any
other mechanism than a squeak that could drive the seals to vibrate at
8000hz. Clearly the looseness of the seal in the rotor slot is a big
factor in getting the squeak started and when the chatter marks become
deep enough, there is probably some kind of orbital motion taking
place. Since the coefficient of friction between the seals and the
housing is an integral part of the squeak process, it suggests that the
SUBTLE DETAILS of the seal/housing lubrication is much more important
than we have heretofore thought.
I've decided that I
_will_ include the oil injection pump and the NRS
ceramic seals in my installation even though I am not planning to
turbocharge it initially.
Just for fun, there are two more clips of the Quicksilver boat in action
on page 3 of this thread:
(
http://ausrotary.dntinternet.com/forums/viewtopic.php?t=57587&postdays=0&postorder=asc&start=0)
Here is some data on the NRS seals that I gathered from the references
above:
>From NRS:
Coeficient of friction would depend on a number of variables; seal
finish, characteristics of the mating materials, lubrication,
temperature, pressure etc.
I am not aware of any controlled tests for COF with ceramic seals
against the hard chrome of the rotor housing. However several speed
shops have seen gains of 20 ft lbs of torque (1 piece) and 25 ft lbs of
torque(2 piece) when switching from steel seals (normally aspirated).
There are two NRS ceramic formulations: Grey and Black
Hardness (Gray) 1650 Vickers- 10kg load
(Black) 1560 Vickers-10kg load
Thermal Conductivity
(Gray) @ 20 Celsius- 65 (Wm/K)
(Black) @ 25 Celsius- 25.6 (Wm/K)
Fracture Toughness
(Gray) @ 20 Celsius- 8.0 (MPam1/2)
(Black) @ 20 Celsius- 6.4 (MPam1/2)
Peter Giljevic (Rice Racing/NRS Australian Distributor) tells me that
Rohan wanted to push the NRS Ceramic Power Seals to the X-Treme limits
therefore they were installed in the rear rotors. Here's how it is:
Mazda Speed ceramic seals in the front rotor and NRS Ceramic Power Seals
in the center with the NRS chamfer to 2mm seals in the rear rotor. This
test lasted about 35 minutes at wide open throttle.
February 16 2005 update: The test results have been backed up by another
grueling session of 26 minutes at full throttle and 9500 RPM @ 22 psi.
Rohan tells me that the stresses on the internals of the engine are
approximately double of what the same engine would see in a car,
especially when the boat comes out of the water under boost and then
slams back down.
Here are some spec's on the boat:
- Hull - Kevlar 1850 bullet, Bravo 1 XR leg
- Engine – X-Treme Rotaries 1962cc 20B (3 rotor) rotary engine, bridge
ported, turbocharged, fuel injected
- Horsepower – 800hp 9500rpm 615 ft/lbs torque
- Speed – max 120mph 9650rpm
- Tuning – by Anthony Rodrigues, Maztech of Melbourne
- Turbo – Garret GT42 1000hp
- Intercooler – PWR barrel water to air
Aubrey
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