How thick are the cylinder walls?

[geekeasy]

I'm in the process of putting my engine back together after the shop repaired some threads in the head, and before I put the water jacket cover on a big and not-insignificantly thick chunk of the cylinder wall came off. You can see it on the left cylinder in the pic.

Should I be freaking out about this and consider getting another engine before I start reinstalling this in my boat?

Or does this seem okay, and this engine is probably good for another 10+ years if properly maintained from here?

[tenders]

It's probably fine. The size of rust is 1.7-2.3 times the size of the original iron (the Pilling-Bedworth ratio) so it is a lot less severe than it looks.

[JOHN COOKSON]

Kick back, have a couple of beers, switch to FWC and you will enjoy life.

TRUE GRIT

[Al Schober]

Agree with John - go to glycol cooling! Like they say, 'Never too soon to quit smoking'.
No idea who Pilling or Bedworth are, but a small bit of iron will make a LARGE bit of rust.