Yanmar 6ly2a-stp 440 problems

Post 34 has probably your best info, at San Juan we switched from the 370 hp to the 440’s when they became available.
The best defense you have is to simply verify Serial numbers and ask if the valves have been replaced, the most common method was to just replace the whole head.
Yanmar had a bad run of valves early on for the 440’s, and have refused to man up.

Fuel lines snapping is just a fatigue issue that happens. The science behind a small steel line cycling such pressures swings up to 1700 times a minute are tremendous. Then the harmonic developed from the engine and this lil steel tube flying around with in it unsupported 2, 3 to 5 inches in length. Keeping or adding more fuel tube inter connect tube clamps may help.
Sadly, Ship happens.

It is a gamble that you have the good valves/heads. Probably the better side of the poker hand.
I understood it was near 90% valves and some 10% valve seats that came apart. Please read my above post before I start a repeating post here.
I doubt Yanmar USA has a good track of their replacements, Self replacement, court ordered replacements or how many heads/engines are dropped in the ocean. I do admit, Yanmar did not care and their gamble worked. They still sell a **** pile of engines,, un phased.

See my Post 63 above. Sorry, I do not have the Serial number range, Yanmar America insists there is no problem. You can try having a Yanmar dealer look up the serial numbers of the boat in question and see if the valves/heads have been replaced.
If you cannot verify that this has been done you are riding a time bomb that can grenade an engine without warning.
Again ask your Yanmar dealer what current costs are to replace the heads, Mack Boring used to have a shelf of re- manufactured heads all ready for these engines.