I agree with Alan. In my 37 years of Bantaming I have had to repair several sets of crankcases due to the discs coming loose. A retired NZ dealer friend was almost bankrupted fixing D14B warranty claims due to the rivets failing.Johnsbantam - New zealand
After the later D7 and some earlier D10 models the discs were added with the intention of closing off the dead space in the crank flywheels so reducing crankcase volume, increasing primary compression ratio and efficiency. But they are not gas tight, volume remains nearly the same.
So leave out, or if rebuilding crank get some good thick plates made, machine the crank lip off, a step inside, clear of the seal diameter and hold on with countersunk cap screws loctited in. Beware the flywheel material is hard and can only be drilled/tapped slowly and carefully. Spark eroding out broken taps is expensive !
I have had this done this on my trials D7, road B175 and racing D14 cranks.
& Thanks Alan