The Yanmar four cylinder conventional and turbocharged (like the Yanmar 4JH2's) are a very different story. Yanmar's have the largest market share of sailboat diesels around the world for reasons that relate to their general quality and durablity.

The two cylinder engines had a "washing machine" feel -- but they are pretty durable.

If you try to add a high output alterator or change the sheaves, you get unintended consequences. Our Yanmar has a Speedseal cover which makes changing the impeller a lot easier; however, when I had a high output alternator put-on. The fabricator built a WONDERFULLY STRONG plated bracket which has little vibration -- but he failed to notch it out to allow someone to take-off the raw water pump itself without removing the bracket. We fixed that this summer when we were chasing-down a problem that didn't exist and tried to (un-necessarily) remove the pump from the engine. (It turned-out that the problem was simple, not complicated; however, I became very familar with the Yanmar's very robust cooling system.)