On our previous boat there was a nice shiny Yanmar that was 20 years newer than the boat. It was flawlessly installed and maintained by the previous owner. In an effort to maintain that standard I bought the Yanmar maintenance manual and decided to do all the recommended checks. So I decided to torque the head. Bought a nice torque wrench, pulled off the valve cover, and let me tell you EVERYTHING looked so good, so clean, working so perfectly, and so I torqued the big bolts, set precisely to the recommended setting, and then I torqued the small bolts. Did I mention I adjusted the torque setting on the torque wrench to the lower recommendation for the smaller bolts? No, I didn't mention it, because I forgot to do it and I proceeded to snap one of the bolts in half, breaking down inside the engine block.

What should have been a 10 minute project became a 10 day project that involved a stranded boat on a mooring ball, diesel AND antifreeze spilled into the bilge, a bolt extractor that mercifully worked, a new, very expensive head gasket, and maybe even a tear or two. In the end we got all it put together nice, but the paint cracked off many of the hoses and the headed gasket leaked oil slightly for the rest of the time we owned the boat. Basically we fucked up a perfectly good engine by trying to the right thing. Still gives me nightmares.