And no protection. Yikes !

Man that's a lot to do in the bilge, I think I would have pulled them if I was you.

Consider my counterpoint. On the trailer, I have to go up and down a ladder to board the boat, and up and down a ladder with an 80 pound cylinder head, 4 times.

On the boat lift, I basically step right on and off, no ladder involved. Way easier.

Sure, it F'n *sucks* manhandling the cylinder head during removal, leaning over into the engine room, no denying that.

Not that this makes it better but that’s a very easy engine bay compared the most.

How are you protecting them father apart?

Yes, the fact that the sunpad/hatch includes the backrest of the rear bench, gives a lot of nice access that most sub-35' boats lack.

I'm not sure I understand your question? I'm a couple of drinks in at this point so that might be on me.

If you're referring to corrosion prevention, I've been using aerosolized corrosion block products like Fluid Film or Boesheild. Reapplying after cleaning/scraping.

So after reading all this, I forgot half of it. Lol, what's the final thought? Maybe the water in the PCV loosened a piece of carbon that got in a valve?

Would be nice to know what product would be good to keep carbon from building up. 502's are not the cleanest about not using a little oil anyway.
I wonder, has anyone used a product long term like SEAFOAM or LUCAS fuel treatments? You can get them by the gallon at auto stores. It's roughly $0.10 per gal to treat with Lucas, $0.40 per gallon to treat with Seafoam.

Any long term users out there, and looked at it to see if it helps keep carbon down?

Best synopsis is this:

Cyls 5-7 had significantly more carbon in the combustion chambers, and it was flaky and easily loosened by the water in the PCV

carbon caused #5 exhaust valve to hang open, kissed by piston top, bent valve and pushrod, banged up rocker arm.

The water in the PCV trick was perfectly safe in the other motor, and in general should be safe, but perhaps it's best to not do it if you're not sure just how much buildup is in there?

I agree that some kind of preventative might be nice to have.

I suspect running synthetic oil would result in cleaner burning of all the oil a 502 uses. Prior owner ran the merc synthetic blend stuff.

Yeah Dr F. G, it's prob not a good idea to use any engine cleaner if a motor is older/dirtier. I used a high powered engine cleaner on an old car one time and it wasn't good. I guess we need to do the water trick more often, like very season then. Haha.

But the exh valve guide sticking from the water/steam washing the oil makes me think though, cause those guides aren't loose, and the exhaust guide doesn't see the incoming wet fuel.

Anybody out there used the water? I've never tried it.

It's funny that boat motors have so many issues. Even under loads as they are, they "should" last many 1000's of hours, like a car. but they don't because they always fail for some particular reason.... other than wear that is. Water leaks, detonation, reversion, are the most common.
I recall GM had a memo out decades ago that stated that very, very little wear occurs when a motor is up and running. It's mostly on startup. And in cases of our boats, it's always some "other" issue.

Maybe the water treatment more often. Carbed water feeding is certainly easier, than using the PCV straw method. I've had lots of success with water treatment.

That flake in the ex port had a long way up to travel if blowing it out was even possible.