The Universal M5421 and M25 are 3 cylinder diesels based on a Kubota D850 engine block. The 5421 was in production from 1978-1981, and the M25 went from 1981 to 1986. Both engines displace 52 cubic inches, and are rated at 21 horsepower. The M25 was replaced by the M25XP which is based on the Kubota D950 engine block. It displaces 57 cubic inches, and is rated at 23 horsepower.
The M25 was initially released with an alternator bracket that was fastened to the timing case cover. In time, this bracket would eventually crack the timing case cover, and spill oil all over the engine compartment. I have read stories of when the case cracked, it allowed the alternator to fall, and short the (un-fused) positive lead to the engine block. This lead connects directly to the 1-both-2-off switch, and such a failure could result in a fire on the vessel.
This is a picture of an M25 with the old bracket (and a new timing case);
This is a picture of the same engine with a new alternator, and the new bracket;
