I finally got into the gear box today and found another issue.  In
 addition
to the sun gear pin failure inside the gear box, the flex plate came
 apart.
I found a piece of it in my cowl as a litte hint of what I was about to
find..

Here are some pictures.  The plate was pretty badly broken up and was only
being held together by Tracys aluminum damper plate and the steel bolt
 ring.
 Pin in sun gear was also broken.  No apparent serious damage, just what
 I
assume is cosmetic galling of the input shaft, adapter plate, and bell
housing from the loose pin floating around.

Thinking back, I had an early sign of it at the Reno Pylon School.  After
one of the races I noticed that my home made cover over the flywheel had
been marred by the flywheel but was not in contact with it.  I attributed
 it
to the high air speeds (205 Kts Indicated coming down "The Chute") somehow
pushing my cover down onto the flywheel.  I put some creases into the
 cover
to make it stiffer which seemed to solve the problem, but perhaps the flex
plate had broken at that time.  With a mis-tracking flex plate it is easy
 to
see that sun gear pins would be undergoing additional stress.  So I am
calling the underlying cause of both issues the flex plate failure.

The large washers that covers the rubber dampers between the dampers and
 the
flex plate have made a significant groove into the aluminum of the
attachment plate.  I have never noticed that before, possibly was a
 function
of the twisting flex plate.  Question is, does it need to be replaced?

My rubber dampers are noticeably worn and soft and need to be replaced.  I
am getting quite a significant amount of oil coming past either my rear
 oil
seal or the oil seal on the gear drive.  That oil may have done in the
rubber dampers, that got too sloppy and stressed the flex plate that
eventually fatigued and broke, which further lead to the pin failure.

So I am undecided on what to do about the flex plate replacement.  I agree
that the iorn flywheel is not the answer.  The machine work would have to
 be
quite extensive, because the aluminum plate rides inside the ring.  After
all that machining, it would have to be re-balanced but that would be
difficult because it has the rear counter weight built in.

Using one of the aftermarket aluminum flywheels might work.  It would
 still
have to be machined to make space for the damper plate, but at least it
would be aluminum (easy to machine) and could then be balanced
 symmetrically
(perhaps even with the damper plate installed so it is all nicely
 balanced.
 That would not be a low cost solution, however!

Paul, if I were to get an aluminum flywheel like this one:


http://www.racingbeat.com/RX7-****1986-1992/Flywheels/11465.**html<http://www.racingbeat.com/RX7-**1986-1992/Flywheels/11465.html

<http://www.racingbeat.**com/RX7-1986-1992/Flywheels/**11465.html<http://www.racingbeat.com/RX7-1986-1992/Flywheels/11465.html
do you think that you could put it on your milling machine and mill in the
resesses for tracys damper plate?  Then would you have any suggestion on
where I could get it balanced?

I am also wondering if I have any business trying to make that much HP.  I
was about to install a water/methanol injection system to be able to use
more boost at Reno.  But it seems I may not be able to safely use the HP
that I already have...

-
--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/ <
http://n4vy.rotaryroster.net/
http://RotaryRoster.net <http://rotaryroster.net/ <
http://rotaryroster.net/

Wow Dave that is a game changer.

I have a guy up here in SZP with a really big lathe that can make
a new "flex plate" . As I recall the subject of flex plate run
out came up recently. Perhaps your plate was warped. Everybody
should check their plates for run out. Any run out puts a bending
stress on the plate due to dynamic imbalance. All parts of the
plate want to revolve in the same plane. If the plate does
not track it will introduce a bending stress in the material.

Also the alignment of the input shaft to the box must be
perfectly in line with the e-shaft axis. This is not easy to
check. Perhaps a low cost laser can be inserted into an empty
gear box starting at the prop bearing end and see where the light
spot falls on the counter weight. A holder for the laser can be made
and checked in a lathe for an aligned axis. If you UPS your empty box,
spacers and adapter plate  up I'll put Jim Poole on the job.

One quick and dirty way is to assemble Tracy's damper on the
input shaft with out bolting it to the flex plate. In fact
leave the flex plate out and off for the moment. Use the engine block
as an anchor for a dial indicator and check for damper plate run out.

Then measure the distance from the block to all four quadrants
of the damper plate.

Paul Lamar


 Dave if you look on the RX-8 flywheel as been redesign by Mazda and those
4
 holes 1" dia plus are located further apart  as the center of the flywheel
 and
 close to the ring gear It looks to me Masda had similar fatigue problem
 with the
 RX-7 flywheel.The problem we can not fit  the Tracy damper plate because
it
 does
 not fit the attaching holes and are to close of the ring gear unless
 someone
 have an other solution


 Jean Prudhomme


 I don't think that is the problem. There are several 3 rotors running
 with that flex plate. Tom Parkes is a turbo 3 rotor no less and
 Mark Steitle's is a p-port 3 rotor with over 300 HP. Please check your
flex
 plate for cracks Mark and Tom.

 This is the first time in 12 years we have a reported failure in the flex
 plate.

 I think it is some kind of alignment or heat problem.
 The rubber bushing can be replaced by fabric reinforced
 silicone rubber washers from McMaster Carr good to 500 F instead
 of only 200 F.

 Paul Lamar

Paul,

I'll check my flywheel this weekend and let you know if I find any cracks.

Mark


 Paul It look to me the RX-8 flywheel is a better design and if it fit on
the
 RX-7 i would like to send you a suggestion by adding an aluminum plate for
holes
 alignment and intall the Tracy damper


 Jean Prudhomme


 You say flywheel but do you mean flex plate?
 The flex plate both RX8 and 13B have six holes.
 The flywheel has no holes in that location.
 Don't use aluminum for this application. Use 4130.

 Paul Lamar


Sorry i means flex plate as you show my photo in mid position


Jean Prudhomme

I also agree that the RX-8 plate looks better, but it would be too hard to
get it to work.  I think that it is bigger.  I can check on that next time I
get to the hangar as I have a turbo flywheel sitting around that is the same
size as the RX-8 flywheel.

I still think that either the lightened steel flywheel (17lbs incl. counter
weight) or an aluminum flywheel (12 lbs - used in racing applications so I
assume it is pretty stout alum) would be the next step up in terms of
strength and at least as easy to addapt as trying to beef up (then balance)
an existing flex plate.  Vs. about 8 lbs for flex plate plus counterweight.

Take another look at these flywheels from mazdatrix  Even the aluminum seems
like it would be much stouter than the flex plate.

http://www.mazdatrix.com/flywheel.htm