This was the valve post 300 hours. Looks like carbon but no rust like I have now...

https://i.imgur.com/niPYMZK.png

There is signs of water there. not much, its multi color and pitting. in my book that's some type of moisture

Are you sure the exhaust is good? things can change with heat. Like inner tube cracks. did you do a visual or pressure test?

Heads might be old enough where you're getting water that's starting to come through the exhaust port. I've seen that before on older heads. Something to check!

Had them Pressure tested 2 times in the last 3 years. Both times they checked out. Doesn't hurt to do them again

Dropped off heads yesterday with machine shop... his first guess was valve guides. He was right. See picture below. Not sure why this want checked during the first top end rebuild. Would have saved me a lot of time and money.

https://i.imgur.com/3rmvPBv.jpg

He is checking other things as well (i.e. Springs, valve job, valves, seals, etc).

Inspected headers. Everything looked good:

https://i.imgur.com/Rhps5ZW.jpg

https://i.imgur.com/r1u5T11.jpg

https://i.imgur.com/om7sYff.jpg

Moses so you for certain have the original cam? Just confirming and didn't catch thread til now. I've ran cams years ago with 5 deg less lsa and a ton of overlap with stock exhaust and have never issues like this. Late 80's learning era. Lol. I didnt idle around much then and when so it was always above 1,200 rpm. I feel bad for your situation and hope you get this resolved. I'm glad to see your valve guides are getting replaced but still gotta get to the root of the problem. This is going on with just the one engine correct? You owned the boat since new? I noticed the white flake over carbon look going on in a couple of the pictures which someone made note and does appear that moisture is heating up the carbon discoloring and flaking the carbon so to speak. Would be my best guess anyway.

But again you went 300 hrs without really many issues other than the what appears to be a moisture issue more so than what your getting now. Did you ck both sides of the head gasket as well as deck surface for any signs of water? I jumped in late here so sorry if I asked already addressed issues.

Yes pray for me!!! To answer some of your questions, yes it is a stock 500 EFI cam which from what I read is 114. Nothing crazy. And agreed based on the 300 hour picture I'd say there is minimal moisture. Nothing compared to what I have now.

Both engines are exhibiting the same issue. Rear cylinders are wet and laden with corrosion.

When pulling the head, I checked both gaskets for water cross porting. So no evedince of anything. I'll post a picture in a minute.

I showed some people my photos they tend to agree with the valve guide philosophy. Reversion tends to clean/steam the carbon out of the port area. As you can see all the carbon looks to be intact. They exhaust flakes do make me wonder a little now.

I just opened the pic of the guides. Ya not good. Surprised he got them out as easily as what he did. what year are these engines? For some reason I recall GM doing something funky with guides on certain year heads etc. Still doesn't appear that really any water is going beyond the corroded erea. No trail or path of least resistance you can see.