Mine is on a Lyc IO-360 with constant speed prop.  The plate is just
under 12" OD and fits the 12" spinner.

Has anyone had trouble with cracks developing around the four mounting
bolt holes?  I think this was original from Lancair since there is a
very similar photo in one of the older catalogs.  It has a very large
hexagonal hole in the center and the four mounting holes already
drilled.  Each of the mounting holes is backed up by a large rectangular
aluminum doubler with four rivets each.

As you can see in the photo, these cracks are severe.  Any ideas?

Tom,

 

Yes.  Part of the problem is with the way the Lancair back plate was formed - it has a slight curl and is always under stress from flexing.  I also noticed two missing rivets.  Are any doublers cracked?  How many hours on the back plate? Another problem is the lack of a bulkhead to stop the spinner itself from moving and causing further flexing of the back plate.

 

Replacing the back plate will not solve the problem unless a bulkhead can be constructed.  If it is a Hartzell prop, it is possible to attach a bulkhead to the forward face of the piston cup.  This assumes the spinner is actually symmetric.

 

I had a similar problem that became critical at about 400 hours.  The glass spinner was starting to crack also.  I bought an aluminum spinner/back plate/bulkhead from Aircraft Spruce that was especially for Hartzell CS props. I also bought doubler plates from Lancair to add to the back plate.  I had to take 3/4" off the depth of the spinner so it ended at the 12" back plate.  I had to discard the bulkhead and turned my own out of 1/4" nylon.  This was not a small project.  The result shows no stress after the most recent 400 hours.