Yes, stators can produce 48 VAC even if the engine is running at normal speeds. Output is dependent on the size of stator. Regulator is designed to reduce it to 12.6-15.2 DCV. Agree with Bert, bad regulator.
And the space between the stator & rotor which under normal production tollerances can vary quite a bit.
A really high voltage is usually because the rotor & stator are not fully concentric so one set of coils that are closer will pump out 48V while the others could be anything from there to 20V.
Because the engine is making 9,000 pulses a minute your meter simply reads the highest voltage.
When you connect to a scope you can see the voltage pulses that you can not see on a multi meter .
Back in the bad old days we used Zener diodes which go closed circuit at 14V so at 14V dc or higher the diode shorts out to the frame turning the excess voltage to heat.
With alternators, the speed & number of turns of wire determine the voltage.
The strength of the magnetic field determines the current.
There is a chance that your stator & rotor ( flywheel ) are not a set.
However to sort that out the mower will have to go to a dealer who can tell the difference between the 3 Kohler flywheels & the stators by sight.
AFAIK there are no numbers on the stator or flywheels.
The danger is if you have a mismatched set all you will do is burn out another regulator and they are not cheap.
Also if the alternator is is matched that is a warranty claim as some one stuffed up at the factory.
