Bent valve
 

I had the boat out over the weekend. It ran good all day then towards the end it started to pop through the carb only at full throttle. I did a compression and leak down test on the cylinders and found that the #1 piston had 0psi compression. The leak down test showed high leakage out of this cylinder too through the intake. I took the head off and found all the intake valve to be seated correctly but the #1 intake valve looked more dished than the others. Is it possible to deform the valve and have it leak like this? It looks like the valve weakened and was almost pulled through the head.

It's more common to see valve tuliping on exhaust valves, but it does happen. Intake valve tuliping is less common since the valves are cooled by the incoming charge.

The engine did over heat once and blew the head gasket as well as introduced water in the oil. I flushed and cleaned out the bad oil and now have fresh. After I got the head gasket replaced it ran for about 8 hours before I experienced this problem. Could the over heating weakened the valve and let it run for some time after before it was tuliped?

Very possible - the valves are cooled through the stem and at the seat - intakes get some cooling from the charge also.

Overheating can weaken metals, and that valve could have gotten hotter than the others. BUT, I'd replace them all, or at least check them all. The other problem when they weaken is broken heads, resulting in massive engine damage.

By broken heads you mean cracked head? Is there something else I should look for when I have the head off?

Broken valve heads, which then work to distroy the cylinder.

IF I had a valve tulip, I'd take off both heads and have them gone through by a good cylinder head shop. I'd also replace the valves - not cheap, but cheaper than dropping a valve head onto the piston. It won't be cheap, and if you have stock heads, you might consider upgrading for a not that much more.

could be the intake valve stuck open,seized the guide, tightened up from the over heating ,