I have actually partially disassembled an opposed piston Fairbanks Morse engine. This was in the early 1990s, and we were removing the antique engines from the dewatering stations around Lake Okeechobee and replacing them with 3,067 cubic inch Cummins 16 cylinder high speed diesels.
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I have very little experience with antique diesels, a few Cummins model Js, Vines, and model Hs, a couple of Detroit Diesel 110s & 149s, some EMD 567s, and one UGLY huge Waukesha V-12. However, I can tell you that for its size this F-M diesel was an unwieldly nightmare to work on. I can see why the railroads would favor the 567s. Servicing was night and day simpler. I cannot imaging working on this thing in a locomotive hood and frame.
-Kevin
Living the dream.
I also understand that the OP engines were uprated in horsepower when adapted from marine to locomotive use. This higher compression was a contributor to piston failures.
My father in law was a foreman at the LIRR Morris Park shops when the FM locomotives were brought on the property. He told me that a former Navy sub machinist could be sent out to a disabled locomotive in a truck with tools and a new piston, and install it in the field. The guys who learned it in FM school weren't taught that, so they had to drag the loco back to Jamaica to do the repair. The Navy wasn't bringing subs back to Norfolk to do repairs, they had a war to win.
Genesee Terminal, freelanced HO in Upstate NY ...hosting Loon Bay Transit Authority, run through Amtrak and CSX Intermodal
CP/D&H, N scale, somewhere on the Canadian Shield