Evan Salant wrote:
I'm thinking about buying a M20J and have a question about the A3B6D
engine. Specifically, why haven't more owners switched to the dual
drive magneto of the A3B6 IO-360 instead of the more typical A3B6
engine with only a single drive magneto. Seems like easy enough to do
at the time of overhaul. Is it a cost issue (unlike core ?) ? Are
there any other issues ?

Evan,

The Bendix "Dual Failure" mag was usually installed by manufacturers due
to space constraints in the engine compartment. Of course, you can
check for STC's to allow the switch, but it's likely that a dual mag
engine just wouldn't fit.

Happy Flying!
Scott Skylane