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I have to say I’ve got several plates from 1-20bs, 3-13brewTt, and 2-RX8’s (series1) that show no evidence of cracking, fwiw. M Sent from my iPhone On Jan 10, 2025, at 8:36 AM, Charlie England ceengland7@gmail.com <flyrotary@lancaironline.net> wrote:
I'm pretty sure David's got it right. I've got a flexplate that's never been run on an aviation engine that's cracked. I really think it's a combination of sloppy design and 'good enough' manufacturing. Look carefully at the lightening holes where the cracks usually start. the holes are punched, with no post-treatment to smooth the sharp edges. Then the sheet is stamped putting stress on the metal around the holes. Perfect recipe for cracks.
Len Hanover (you still here, Len?) once speculated that the scrap yards were cracking them by sitting the engines down on the flexplates, but I think they're just cracking from mfg-induced stresses and vibration; even in the car.
Charlie
Automotive tech for 40 years, 25 years Cadillac. I saw quite a few cracked flexplates. Why, some were self diagnosed, corrosion between starter and eng. block changed geometry, witness marks that cust. would try to start a running eng., loose torque converter bolts, loose trans to eng. bolts, wrong starter held on with one bolt. When I was seeking a Mazda RX7 flexplate for out project, first three were cracked right out of the cars. I think our starter is shimmed out 1/16", original RWS PSRU-RD1-B, original starter position.
What i can rember was this also a topic on the late Paul L group discussion.
Maybe Dave Leonard can chime in - think more that it was gyroscopic forces that craked the plates
Maybe i can find the photos and topic in my old mails
Sent from my iPhone
Le Roux Breytenbach
Maybe some of the cracking flexplates are resulting from starting issues, the starter motor can hammer the ring gear if not meshing correctly or if engine misfires on start. may explain why so many flexplates come pre-cracked from the wreckers.
Andrew
Hi M
I was wondering the same thing.
What I discovered first of all was that flex plates are designed to flex (funny that) and cracking is not limited to our setup.
There are companies that specialise in stronger flex plates, particularly for modified and higher horsepower engines.
Since our engines are being used at a higher horsepower per unit time and therefore higher stress (assumption) perhaps our setup could be likened to race applications.
But then our hours of use would be significantly lower (assumption) than an average vehicle, but perhaps not a race application.
Is the cracking we are seeing consistent with race applications? But they dont race automatics, do they?
So my take on this is that perhaps the flexing of the plate in our setup is to some extent higher than OEM.
Our options seem to be:
1. Replacing the OEM flex plate with a stronger part. Steve B being the latest going down that track and in his case also removing the rubber isolation in the process.
2. Connect direct to the eccentric shaft and therefore taking the stress off the Flex Plate doing away with the damping mechanism which Tracy did, and perhaps is still doing. Would be real nice to know.
Like M, I would appreciate hearing what others know or are thinking or doing.
Steve Izett
> On 10 Jan 2025, at 2:15 am, Marc Wiese cardmarc@charter.net <flyrotary@lancaironline.net> wrote:
>
> Has the cause of these cracks been uncovered, and if so, what is the current thinking on it? An AL racing plate?
> M
> Sent from my iPhone
>
>> On Jan 9, 2025, at 1:31 AM, Steven W. Boese SBoese@uwyo.edu <flyrotary@lancaironline.net> wrote:
>>
>> Steve,
>>
>> I didn’t see the cracks prior to disassembly and doubt that they could have been seen on the counterweight side very well -if at all- when assembled.
>>
>> I replaced the Flexplate with a steel flywheel about a year ago. Since then, I replaced the four rubber dampers with machined aluminum discs giving a solid connection and then dynamically balanced the system. This was done because maintaining a dynamic balance wasn’t possible with the dampers. Only a few hours of flight have occurred in this configuration so far and there has been no indication of problems resulting from this change.
>>
>> Steve Boese
>>
>>> On Jan 8, 2025, at 11:03 PM, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:
>>>
>>> ◆ This message was sent from a non-UWYO address. Please exercise caution when clicking links or opening attachments from external sources.
>>>
>>>
>>> Hi Steve
>>>
>>> Is this recent then?
>>>
>>> I’m not able to get to my aircraft at present to check my flex plate which has probably seen 50 hours of service.
>>>
>>> Was it possible to see these cracks assembled?
>>>
>>> I would appreciate your reflections on Tracys latter choice to remove the damper, and particularly when using a timber/glass prop such as an MT.
>>>
>>> It would be great to have an update and current info from Tracy regarding his no damper hours if anyone can contact him.
>>>
>>> Very helpful, thanks again Steve
>>>
>>> Steve
>>
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