YSE is not a separate manufacturer but a model line: the Yanmar YSE series of marine auxiliary diesels, best known through the YSE8 and YSE12. These two-cylinder, raw-water-cooled engines were installed in thousands of sailing yachts during the 1970s and belong to the same family tree as Yanmar's YSB and YSM engines, which the later GM and QM series eventually replaced.

Simplicity is the YSE's defining virtue. With straightforward mechanical injection and few electronics, a well-maintained example still starts reliably and sips fuel, which is why so many remain in service decades after installation. Age is also the challenge: cooling passages, injectors and gaskets all deserve systematic attention on engines of this vintage. Good spares availability keeps rebuilds realistic.

The YSE manuals collected here document routine servicing and full overhauls alike: fuel filter and injector service, injection pump timing, water pump and cooling system work, cylinder head removal and valve grinding, gearbox oil and coupling checks, and electrical starting circuits, with torque specifications and clearance tables throughout. Hand-start provisions are documented where fitted.

Owners of classic yachts, restorers re-engining or rebuilding an original installation and marine technicians who see these engines regularly will find these documents the definitive reference. Pair them with our broader Yanmar collection for anything the YSE shares with its engine siblings. Model and serial details in each listing confirm coverage before purchase.