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Neil,
So the 0.5 - 1" movement is the normal gear lashing plus any deterioration of the rubber flex coupling? That would make more sense than how I originally interoperated the prop movement.
"Bearing stack, if you use my shaft exactly the same stack required."
I have an inquiry in to Tracy about the feasibility of changing the bearing stack order. I've inspected four C model gearboxes and two of the units have some input shaft wear where the 1mm thrust washer is contacting the shaft. It has been suggested that swapping the 1MM and 3MM thrust washers should eliminate the shaft wear between the two thrust bearings. However the 1MM thrust washer will not capture on the input shaft for assembly. I have been unable to locate a 1MM / 35MM shaft thrust washer large enough to mount to the aluminum plate. I've attached a possible design that I have sent out for quote. One change is that the mounting tabs cut at the washer would need to include a radius to minimize stress fractures. Problem is the company has a $200 minimum setup fee.
Bobby
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Wednesday, November 07, 2018 3:21 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: cushion drive - retrofit questions.
Bobby,
There is no need to replace the input shaft on the
RD1-C just to fit my cushion drive. My input shaft is identical except
it is machined from solid and a one piece shaft.--- and much dearer!
Bearing stack, if you use my shaft exactly the same stack required.
Yes snubber washer thickness is unique as distances vary slightly. I am
happy with 5 - 10 thou clearance as the washer is to only contact when
the prop is driving the engine which allows the input shaft to move
forwards. The snubber washer simply prevents metal to metal contact in
that situation. I do know of one redrive that is operating without the
washer at all and all it seems to do is allow oil leakage from the seal
on the input shaft as it travels back and forth, (if it actually does?)
End play I believe is difficult to check as drag on the parts, when
stationery, seem to make shaft movement impossible. But it is possible
in theory for the shaft to move, hence the nylon washer. As you say
gear lash is simple.
Neil.
On 11/8/2018 1:34 AM, Bobby J. Hughes bhughes@qnsi.net wrote:
> Neil,
>
> I've got a few questions about the input shaft replacement.
> Does the replacement input shaft use the same thrust washer stack at the RD1-C?
> If a replacement shaft was retrofitted how does that affect the molly infused snubber washer tolerance? I believe it would be unique for each drive. Not sure what the acceptable tolerance range is.
> 0.50 - 1" movement seems like a lot. There may be some movement in my RD1C but I'm not aware of it. I check lashing and endplay before each flight but never noticed any movement other than lashing.
>
> Thanks,
>
> Bobby
>
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
> Sent: Wednesday, November 07, 2018 12:15 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] cushion drive
>
> Charlie, Photo attached,. Should the rubber fail then the inner drive block will simply lock up on the outer square giving metal to metal which should last quite some time (hours) before wearing either away. The rubber is "engine mount" rubber so will only deteriorate slowly and not just explode and disappear completely. To test for wear you simply rock the prop and any more than 1 inch movement would suggest a problem as in deterioration in the rubber. I can only get a half inch movement which is in the gear drive train. The rubber can be re-vulcanised if it is ever necessary. I have now in excess of 50 hours with the rubber insert for no visible wear..
>
> Neil Unger.
>
>
> --
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