i think it had a lot to do with the environment and operating conditions. if you think about it, marine and stationary applications have pretty much constant temperature and other conditions. also, the engine runs at a fairly constant speed, usually where it is happiest and most efficient.
the railroad world is somewhat more harsh and the power output needs are constantly changing. guess fm's just didn't do so well under those conditions. the emd engines might not have fared so well in the applications that suited the fm's but that is a guess.
Charlie
Here's a neat cutaway of the F-M engine:
A problem I can see is that you can't get to the "top end" without disassembling the engine. No ring changes, no piston changes, no wrist pin changes.
Another problem is sort of self-fulfilling: If you have orphan engines, there's fewer people who know how to take care of them. It's a tough fight for the new guy to get market share; and, at first, they have to do the old Avis trick of "trying harder". A lot. Keep in mind that EMC, when they were first sending out their newfangled diesel locomotives, placed an employee on every freight locomotive to ensure an absolute minimum of angst for the purchaser. Or so I recall hearing. This cost them big bucks. Perhaps F-M didn't supply adequate support for its product. I am uninformed on that matter. But I have read that SP&S dropped Baldwin when Baldwin didn't get them replacement parts in a timely manner. And Baldwin is long, long gone from locomotive production.
Ed
I was watching the old Trains magazine video. The host mentioned that FM engines are widely sought after for marine and stationary applications.
My questions is, if the FM OP motor was so good, why did FM fail in the locomotive field?
What issues did the RRs have with this design?
Jim