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In a message dated 10/28/2018 5:49:12 PM Eastern Standard Time,
flyrotary@lancaironline.net writes:
As a heads-up to new
arrivals, the flexplate cracking issue likely
predates use of the engine in aircraft. I've got one
that's never flown that has two cracks. I think Len
Hanover mentioned that mishandling at wrecking yards
may be one cause (dropping the engine on the
flexplate when storing it). It doesn't seem to be
limited to rotaries, either.
Bottom line
for me is to check before using. That's how I
discovered cracks in mine.
Charlie
Hi Joe,
Yes, my flex plate not only developed cracks
but basically disintegrated. Keep in mind that I
was running about 300hp at rookie school for
Reno. None the less, the flex plate was never
designed to transmit the output of engine, just
allow the starter to turn it over. The lightening
holes in it alow flexing that initiated the
cracks, then the whole thing shattered.
Surprisingly, in my case the pieces happend to jam
together in such a way that it still functioned
until I happend to find it on inspection several
flight hours later.
All the details of my fix are in the archives
somewhere, but basically I replaced the flex plate
with an off the shelf lightweight flywheel that I
addapted to accept tracys damper plate. I took it
to a machine shop to have the mounting holes
correctly placed. I also had it balanced, but I
probably could have skipped that step. I also had
to machine a recess into Tracys mounting plate to
allow the starter to reach the teeth on the
flywheel. Details are in the archivees
somewhere. That was going on in June July and Aug
of 2011, which may make it easier to find.
Tracy also engineered a fix. His solution is
in the archives too. He also seemed to think that
the flex plate was good enough for a normially
aspirated 13b, but after seeeing what happend to
mine, I believe that even a n.a. 13b would
eventually fatugue the flex plate into the same
result. As I recall, at least one other person
detected cracks in the same place.
Best,
Dave Leonard
I believe
that Dave Lenard had an issue with cracks
appearing in the flexplate. He came up with
a solution and does anyone recall the
details of the solution and would it work
for all 13bs with Tracy’s PSRU?
Joe Berki
On the
racer, I built a small steel flywheel just
big enough to fit up a 5 1/4" Tilton dual
disc clutch pack. The front side needed to
have about 1/4" spigot so as to clear the
flex plate which has a slight conical
shape. I just bolted the flywheel on over
the flex plate. Never a problem on the 95
RX-7. a big problem on a sports racer I
built. The driver defeated the rev limiter
by shifting into 1st rather than 3rd while
already turning about 9,500 RPM. The
transmission was a Hewland FT-200, dog ring
style, so it went right into the selected
gear. The flex plate has only 6 welds to
keep the ring gear on the flex plate. The
ring gear broke next to one weld. The free
end tried to machine the bell housing into 2
pieces. The ring gear also rolled outboard
about 30 degrees. It wanted out and almost
made it.
On the
replacement ring gear I TIG welded an
additional 6 welds and added 12 welds to the
back of the ring gear.
Since you do
not need a wear surface for the airplane
installation, just a piece of aluminum plate
could be used to produce a similar flywheel.
The flex plate is just used to start the
engine and delivers no torque loads to the
gear box.
Lynn E.
Hanover
Len, if Tracy's damper plate is used, it bolts to the flex plate,
just inside of the ring gear. So for our purposes, the flex plate
does deliver torque loads to the gear box.
Charlie
(apologies for the random order of posts)
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