RE: Difference between OS 46 fx, and fxi?
I had heard that the FXi designation was used to differentiate the later engines from the early .46 FX engines that were prone to peeling liners. The rumor mill said that the FXi engines were made with an improved plating process that kept the nickel where it was supposed to be.
I own both .46 FX and .46 FXi engines and find them identically outstanding in terms of performance and reliability.