Well if the motor was knocking and it was the marina that said 'just go easy on it', if you take it to that marina for a rebuild, it will most likely involve you dropping your shorts and grabbing your ankles.

Interesting -- sounds exactly like my symptoms -- which felt almost like a small backfire versus metal on metal contact. I also did notice a little bit of smoke coming out of the intake.

Obviously not what I'm hoping for given that means full rebuild.

That being said, I wasn't given the compression # over the phone, so perhaps the "no compression" I was told was very low compression.

It seemed to -- just not above a certain RPM. It also had a hissing sound at idle, once the motor was warmed up.

Update: Leakdown test apparently did not reveal anything through the crankcase, so they're pulling the head.

since you overheated it, you may have cracked a head and tuliped an intake valve. Just saying this to make sure they magnuflux the head because a crack can be very hard to see.

Marginal injectors may not manifest their problems until at higher throttle settings when the motor needs the fuel but the injector can't keep up. Cylinder goes lean, detonation ensues, timing is retarded which delays the combustion event, elevates exhaust temps. Intake valves begin to tulip, valves and valve seats take a royal beating as do pistons etc. You may or may not hear, or more likely feel, a slight miss at cruise speed.

Motor will also tend to lay down at the upper end.

What do you mean by lay down at top end?

Injectors are often overlooked. I just roached a piston in a 502mpi due to a #6 injector that flowed 24% less and had a chitty spray pattern. Luckily I caught it quick and could do a garage repair without full tear down. Still sucks though. Worst part is I blew it up at an easy sustained cruise not WFO. Just bought boat this spring and was already planning on full rebuilds this winter. Had notion to pull them when I first bought it and have them tested after learning how inconsistent Merc injectors are. Boat ran great every time until it didn't. Piston lost some ring land material, chunked pieces of top ring and embedded in top of piston. Heat cracked the exhaust valve. Got lucky with hardly any cylinder or head damage.

Injector testing WILL become a standard preventative maintenance item from now on.

betting there is a valve tulped bad or piece missing..

What does a "tuliped" valve mean?

cylinder overheats causing exhaust valve to become malleable and extrude.