GOOD NEWS!! WE JUST GOT FAA-PMA FOR THESE IMPROVED SPINNER BACKPLATES.
I have developed an improved spinner bulkhead (back-plate) for the rear engine for my 337F. We made some extras if anybody has crack issues. We developed these for a commercial operator. You have to pull the prop to find the cracks. It is worth the trouble since most of them are cracked! The original Cessna is stamped from annealed 6061 aluminum and Cessna depended on the stamping process to work harden them. The problem is that where they crack at the bolt holes there is no forming to strengthen the soft aluminum. My bulkheads are spun from annealed stock twice as thick as the original and heat treated to T4 and then we re-spun them to take out the heat treat distortion. This gives them about 15 times the high frequency cyclic load crack resistance of the original Cessna part. They are then lathe machined for a final true and lightened back to the original weight. After the hardware is installed they are then epoxy primed and balanced to within 2 grams. Log book entry is all that is required. Contact me for more info
davem@mcfarlaneaviation.com.