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 tofind..

Here are some pictures.  The plate was pretty badly broken up and
was onlybeing 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 Iassume is cosmetic galling of
the input shaft, adapter plate, and bellhousing from the loose
pin floating around.

Thinking back, I had an early sign of it at the Reno Pylon
School.  Afterone of the races I noticed that my home made cover
over the flywheel hadbeen marred by the flywheel but was not in
contact with it.  I attributed  itto the high air speeds (205 Kts
Indicated coming down "The Chute") somehowpushing my cover down
onto the flywheel.  I put some creases into the  coverto 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  tosee that sun gear pins would be undergoing additional
stress.  So I amcalling the underlying cause of both issues the
flex plate failure.

The large washers that covers the rubber dampers between the
dampers and  theflex plate have made a significant groove into
the aluminum of theattachment plate.  I have never noticed that
before, possibly was a  functionof 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.  Iam getting quite a significant amount of oil coming
past either my rear  oilseal or the oil seal on the gear drive.

 That oil may have done in therubber dampers, that got too sloppy
and stressed the flex plate thateventually fatigued and broke,
 which further lead to the pin failure.

So I am undecided on what to do about the flex plate replacement.

 I agreethat the iorn flywheel is not the answer.  The machine
work would have to  bequite extensive, because the aluminum plate
rides inside the ring.  Afterall that machining, it would have to
be re-balanced but that would bedifficult 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 itwould 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
do you think that you could put it on your milling machine and
mill in theresesses for tracys damper plate?  Then would you have
any suggestion onwhere I could get it balanced?

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

-
--
David Leonard

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

Yes, it is becoming pretty clear that any option other than the auto-
tran flex plate is going to take considerable extra work to get it
addopted.  I think the aluminum fly wheels are my first choice of
alternative at this time, but I may just put in the flex plate and
stop trying to make a lot of HP.
--
David Leonard

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

I would not use aluminum Dave. IMHO a better way is use fatigue  resistant
.065" thick  4130 sheet reinforcement tig welded in the center
diameter. I'll build you one out of a spare plate I have if you will
work on finding a replacement.

Paul Lamar

 Hi Dave,

 I gather from your e-mail and web that you are a Naval Aviator. This would
 tell me you are used to aerobatics, which will put assorted higher stresses on
 the airframe. I was having a morning coffee and contemplating navel lint when
 I came to the idea to check your web and construction photos. Also this came
 to the forefront after the pylon school with high stresses.

 Your PSRU mount on the plate has a fairly small diameter ring of bolts. During
 aerobatic manoeuvres, there will be a large torque on the prop that will be
 transmitted through the PSRU to the mount plate. I believe the flex should be
 determined and dealt with.

 So, how to measure and calculate the flex force. A hydraulic cylinder like
 used with a pump for body work can be modified to have a pressure gauge and
 the cylinder diameter is easy to find.  This will tell the pounds force. If
 this cylinder is extended a bit (1/2 stroke) and a bottle jack is used under
 it to apply force, then a dial indicator will show the amount of flex. Put the
 hydraulic jacks under the front of the PSRU just behind the spinner. A piece
 of angle or channel iron bolted on the top of the engine (the lift bracket
 bolt hole) will provide a mount for a dial indicator, to read movement on the
 top of the front of the PSRU. Paul should be able to do a quick calculation of
 the force applied through the prop during turns.

 You may need to install braces from the front of the PSRU back to the engine
 bellhousing bolts to stiffen it up. A small amount of flex is like a
 misalignment and under load it will not take long to break the flex plate.
 Brace to the sides as well.

 Dale Davies




David I sent an idea of using the RX_8 flywheel with an additional aluminum plate,the RX-8 look a stiffer design


Jean Prudhomme

Yes it does look stiffer Jean but it would require a new Tracy style damper plate because I suspect it is larger in diameter.

I think the cracks started in these holes.
The 13B plate is only 1.5 mm thick or about .059".
I think the holes could be filled in with .065" thick 4130
and it would be much stronger. Also a 4130  doubler plate
could be added to the center. This is all low cost.

Aluminum is not a good material for this use.

Paul Lamar