Without enlarging the drain line, the internal pressure in the gearbox will be in the range of 2 to 4 psi and applied to the input shaft seal even with a groove cut in the mount plate.

Steve Boese

On Apr 30, 2021, at 8:45 AM, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:



For what it's worth, I had a leaking input shaft oil seal. Possibly from bad installation (bore badly scratched).
I tried to polish out scratches along the shaft (no clue how they came about), but still visible.
On Tracy's recommendation I cut a small groove in the mount plate to prevent any pressure build-up behind the input shaft thrust bearing. (The factory groove in the input shaft, that supplies the thrust bearing with oil, varies from shaft to shaft and was not under Tracy's control.) 
I installed a double-lipped SK9862 oil seal.
So far no more leak!

But the point is that you can eliminate pressure build-up behind the thrust bearing that might want to force out the oil seal by cutting a small grove in the mount plate, providing a path for the oil to return.

Hand cut with a dremel. Not pretty, really wanted it deeper than wide.

BTW, I'm using the mount plate from my old (crashed) RV-3. The one I got with the drive from the Cozy-girls had starter position in wrong place and designed to bolt to a engine mount plate under the engine.

Finn

On 4/30/2021 2:00 AM, Sboese sboese@uwyo.edu wrote:

Neil,

With a -6 drain line to the crankcase, air that was initially inside the gearbox is mixed with the oil and this mixture is forced out the drain by an equal volume of pure oil coming in.  Eventually all the air is eliminated and the gearbox is completely filled with oil.  An RD (Tracy Crook) redrive fitted with a -10 (5/8”) id drain and a vent from the upper part of the redrive to the upper part of the crankcase will not fill up with oil and only have crankcase pressure inside.

Steve Boese 

On Apr 29, 2021, at 4:25 PM, flyrotary@lancaironline.net wrote:

Mat,

                Oil into the redrive is needed mainly for lubrication and also heat transfer.  Very little is needed as lubrication needs little with oils these days.  It appears that In most cases the redrive actually fills and does not drain readily.  Why I do not know.  This puts pressure on the seals back and front, which suggests it may be beneficial to hold both seals in with small screws to prevent them getting pushed out.  Screws are good insurance as in flight a detached seal could ruin a good day.

Neil.

 

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