On 28 Nov 2023, at 5:11 pm, David Leonard wdleonard@gmail.com <flyrotary@lancaironline.net> wrote:

There is really no such thing as an AD for these non certified parts.  Yes, my redrive is the RD-1B with the 2.17:1 ratio.  The part that fails here is the connection of the sun gear to the input shaft. The input shaft fits inside the sun gear and they are fixed in place with either a weld or a pin or two.  The pin is about 3/8 in diameter.  

I believe the RC-1C uses the same input shaft and sun gear, but I am not sure.

This is a different issue from the flywheel.  The original design called for the use of the auto transmission flex plate to transmit the torque loads from the engine output shaft to the plate with the dampeners.  However, in the car this was only used for starting, and not to transmit the whole power of the engine.  Over time they tend to flex and crack.  There are a couple of different solutions including replacing the flex plate with a flywheel like I did.

The 3rd failure mode that I came across was my failure to supply a dedicated oil line from a high pressure area which caused the plain bearings to seize.  However, that was at Reno with high power and high gyroscopic loads.

Dave Leonard

On Mon, Nov 27, 2023 at 10:33 PM Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:

Hi Guys.

Has an AD been issued on the RD1-C PSRU?

How many of these failures has there been?

Now I’m thinking I understood yours Dave was an earlier version with a lower ratio but the shaft assembly may be exactly the same.

Do you both have the damper with original shore hardness donuts? I recall Dave changing to a modified low weight steel or ali flywheel.

You have my attention!

Steve Izett

Genesis 4 Port RD1-C MTV-7C

On 28 Nov 2023, at 12:07 pm, David Leonard wdleonard@gmail.com <flyrotary@lancaironline.net> wrote:

Hi Dennis,

This happened to me 3 times, Once with the older style weld, and then twice with the pin.  After the pin sheared for the second time I sent it back to Tracy and he placed a second pin 90 deg to the first one.  That fix has held up for a couple hundred hours including racing at Reno (appx 300h.p.).

Of note, 2 of the failures occurred during long gradual descents at low power.  The other occurred after a backfire during start-up.  I have a suspicion that low power descents cause the prop and engine to alternately overrun each other causing a rapid hammering back and forth.  This problem is made worse by the somewhat lax gear leash that Tracy designed into the PSRU.  I believe that was a good choice for normal operation but may make things worse during periods when the plane is pushing the prop yet enough power is being produced to cause the torque to alternate directions.

So in addition to the 2 pins, I now make sure that I keep adequate power applied throughout descents so that the torque remains positive.  In steep descents idle power will probably allow the torque to remain negative which is also OK.

Hope you are doing well, glad to hear that you are still flying. A machine shop should be able to place a new pin and machine a hole for a second pin.

Cheers.

David Leonard

Turbo Rotary RV-6,  N4VY

On Mon, Nov 27, 2023 at 7:09 PM Dennis Haverlah clouduster@austin.rr.com <flyrotary@lancaironline.net> wrote:

The shaft between the RX-8 engine and the reduction drive unit has a gear secured to the shaft with a steel pin.  (The gear drives the planetary gear set). The steel pin sheared off allowing the gear to rotate on the  shaft.   I understand this has happened to others in the past.   I’ve heard that several fixes were proposed or tried – welding the pin to the gear, doing more deforming of  the pin at the gear surface or installing a tighter or larger pin.   I have another new shaft/gear assembly I plan to install  after I incorporate  improvements. 

When the pin sheared the gear only rotated about 3/32 inch on the shaft. The two pieces of the pin outside the shaft were thrown out of the gear and apparently were chewed into very small particles by the  planetary gear assembly. 

 

Any info. You may have will be highly appreciated!

I have about 920 hours on my RX-8 engine in my RV-7A

 

Dennis Haverlah

512-921-0636

 

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