What happens to hour meters with an engine swap?

Who knows… usually the hour meters are left alone. How many hours are they showing?

Gee, new stuff keeps track in its ECM.

When we replaced gen-sets and old engines, we replaced the hour meter.

I can confirm that there's absolutely nothing electronic in the Cat 3116.
In the event of a catastrophic electric system failure, your only engine problem would be that you must go down the e/r to turn them off, by manually pressing the red button on the stop solenoid.

As a consequence, you (as well as the previous owner) can connect to their key contact any hour meter you like, and replace them whenever you wish.
In other words, the short answer to your question is... Who knows?

A run fuel solenoid. Needs B+ to run.
Key off, kills this and the engine.

Not sure of what are the FL engines you're referring to, but if you mean that with no DC you were unable to stop the engines because the stop solenoid didn't have any manual/mechanical stop button, that's indeed weird, if not downright dangerous.

On the other hand, if their stop solenoid were "powered to run" as CR suggested (rather than powered to stop), the engines should stop there and then, as soon as DC is missing for whatever reason.
Which imho is actually worse, but that's true of many modern electronically controlled engines.

Aha, I didn't think of Ford Lehman, also because they are almost unheard of, in Europe.
Anyway, I see what you mean, and it's exactly the same as in the Cat 3116 of my old boat, or also the mechanic MANs in my current one.
That's all gone by now with electronically controlled engines, which would leave you stranded wherever you are, if DC would be lost.

I m not sure how you would loose all DC especially on a twin engine boat. If properly designed, each engine and gen should have its own battery plus a house bank. In theory that should prevent a complete failure.

Sadly, the things you have to find out the hard way; about previous owners and then the boat.

In the old days (real old); for rebuilds, original hour meters were left intact if they still worked (usually did). Hours were on the block/crank for life.
The ships log would show hours when services including top-end or overhaul was preformed.
So, a meter that shows 8K hours, and the log shows records and receipts of two majors was the standard.
Sadly, no proof, no pudding. I don't believe anybody now days without a stack of records.

Then, new to the boat equipment got new hour meters.
Sad part of these new meters, failures were common. Like float switches, lucky to get good ones..
FM

The gauges at the helm should have shown the alternators were not charging. You probably had some loads on overnight as the fresh water pump and the bilge pump should not have killed the batteries. Unless the banks are too small.

Does the boat have a parallel switch, that would explain both banks dying. Parallel switches should only be used for start if needed and not left on

That’s a crappy set up