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Date: Sun, 17 Jul 2011 23:25:08 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Flex Plate Failure - Improvements
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On 07/15/2011 08:48 PM, Mark Steitle wrote:
> Guys,
>
> I removed the flex plate from my 20B today and found a crack.  So, as 
> they say, "I now have skin in the game."  I was out in the garage 
> tonight, contemplating this problem and a possible solution came to 
> me.  I'll run it by you guys here and see what you think.
>
> Comparing the 20B flex plate to a picture on the Mazdatrix web site, 
> it appears that the 20B auto flex plate is identical to the Renesis 
> auto flex plate.  The outer dimensions (ring gear) and offset from 
> eccentric shaft flange to outer edge of ring gear of the 20B flex 
> plate is the same as the 13B plate I removed from my 20B today.  The 
> Renesis/20B plate has a more gradual dish shape than the 13B, and is 
> thicker too.  Since I had a spare 20B flex plate and a spare 13B flex 
> plate, I took a few quick measurements, and it looks like the 13B flex 
> plate could be easily made to nest down inside the 20B plate by 
> removing the 13B's ring gear.  That would allow for the two plates to 
> be bolted together using the four 20B outer bolt holes along with the 
> six crank bolts in the center (when installing on engine).  Then the 
> existing redrive adapter plate could be attached using the original 
> four existing bolts existing in the 13B plate.  This would leave the 
> RD2-C aluminum adapter plate offset by the thickness of the 20B flex 
> plate (.090"), and would result in a much stronger flex plate.  I 
> calculate this would increase the FWF weight by about 4 lbs.
>
> Comments?
>
Sounds like a lot of work to get to overkill.  Why not just bolt some 
rubber disks to the adapter plate so that they fill the lightening holes?

The plate is plenty strong enough as long as it doesn't actually flex.  
Which begs the question of why to they call it a flex plate..but I 
digress.  Add four more points where the plate is tied to the adapter 
plate, and the slight flex will be eliminated.  Only a few oz of extra 
weight, and no machining.