As a heads-up to new arrivals, the flexplate cracking issue likely predates use of the engine in aircraft. I've got one that's never flown that has two cracks. I think Len Hanover mentioned that mishandling at wrecking yards may be one cause (dropping the engine on the flexplate when storing it). It doesn't seem to be limited to rotaries, either.

https://www.google.com/search?ei=kizWW_L1KYOuzwKdkaLYBA&q=+flexplate+crack+symptoms&oq=+flexplate+crack+symptoms&gs_l=psy-ab.3..0.9099.9099..10752...0.0..0.153.153.0j1......0....1..gws-wiz.ntPTjk3KElA

Bottom line for me is to check before using. That's how I discovered cracks in mine.

Charlie

On Sun, Oct 28, 2018 at 12:48 PM David Leonard wdleonard@gmail.com <flyrotary@lancaironline.net> wrote:

Hi Joe,

Yes, my flex plate not only developed cracks but basically disintegrated.  Keep in mind that I was running about 300hp at rookie school for Reno.  None the less, the flex plate was never designed to transmit the output of engine, just allow the starter to turn it over.  The lightening holes in it alow flexing that initiated the cracks, then the whole thing shattered.  Surprisingly, in my case the pieces happend to jam together in such a way that it still functioned until I happend to find it on inspection several flight hours later.

All the details of my fix are in the archives somewhere, but basically I replaced the flex plate with an off the shelf lightweight flywheel that I addapted to accept tracys damper plate.  I took it to a machine shop to have the mounting holes correctly placed.  I also had it balanced, but I probably could have skipped that step.  I also had to machine a recess into Tracys mounting plate to allow the starter to reach the teeth on the flywheel.  Details are in the archivees somewhere.  That was going on in June July and Aug of 2011, which may make it easier to find.

Tracy also engineered a fix.  His solution is in the archives too.  He also seemed to think that the flex plate was good enough for a normially aspirated 13b, but after seeeing what happend to mine, I believe that even a n.a. 13b would eventually fatugue the flex plate into the same result.   As I recall, at least one other person detected cracks in the same place.

Best,

Dave Leonard

On Sun, Oct 28, 2018, 4:23 AM Joseph Berki jskmberki@windstream.net <flyrotary@lancaironline.net> wrote:

 

I believe that Dave Lenard had an issue with cracks appearing in the flexplate.  He came up with a solution and does anyone recall  the details of the solution and would it work for all 13bs with Tracy’s PSRU?

Joe Berki

 

On the racer, I built a small steel flywheel just big enough to fit up a 5 1/4" Tilton dual disc clutch pack. The front side needed to have about 1/4" spigot so as to clear the flex plate which has a slight conical shape.  I just bolted the flywheel on over the flex plate. Never a problem on the  95 RX-7. a big problem on a sports racer I built. The driver defeated the rev limiter by shifting into 1st rather than 3rd while already turning about 9,500 RPM. The transmission was a Hewland FT-200, dog ring style, so it went right into the selected gear.  The flex plate has only 6 welds to keep the ring gear on the flex plate. The ring gear broke next to one weld. The free end tried to machine the bell housing into 2 pieces. The ring gear also rolled outboard about 30 degrees. It wanted out and almost made it.

On the replacement ring gear I TIG welded an additional 6 welds and added 12 welds to the back of the ring gear. 

Since you do not need a wear surface for the airplane installation, just a piece of aluminum plate could be used to produce a similar flywheel. The flex plate is just used to start the engine and delivers no torque loads to the gear box. 

Lynn E. Hanover