[Finsleft258]

That head has been removed and not reinstalled properly. Those bolts to hold it in are a mix of SAE SS, factory metric hardware, and it appears to be SAE zinc plated grade 3, 5, and 8...basically a hodge-podge of bullshit.

The heavy corrosion you are seeing at the base of the plugs is from the water jacket cover leaking around the plug locations. Likely, that gasket wasn't replaced along with the head gasket. order both, clean the surfaces, and reinstall. You are relegated to using the hardware sizes now in use (thought they can all be SS) as the SAE ones will have been drilled an tapped.

 

[Finsleft258]

Good eye!

Thank you, sir! Engines and corrosion are firmly in the wheelhouse.

 

[Finsleft258]

I should have noticed the odd assorted bolt heads. I bet the previous owner pulled the cover and reinstalled and didn’t replace the gasket.

Agreed. The washer stack is epic, too.

 

[Finsleft258]

The moment I look under the cowling and see mis-matched bolts or buggered up screws - I run the other way... Yes, a competent mechanic can sort it out but I'm always worried about what I can't see when some "shadetree" type has been messing where he shouldn't have...

I'm less worried about mismatched hardware and more worried about the cleanliness of the repair. The hardware just indicates that a repair was performed. The type of hardware (steel where SS or stretch bolt should be) or the wrong type of sealant (or worse, sealant where there shouldn't be) are the biggest indicators for me. This thing has them all.

OP... The engine may be perfectly fine, but the repair needs to be properly done for the engine to have a full lifespan.

 

[Finsleft258]

Well as ive stated before, im no mechanic! But, i did notice the gasket and mismatched bolts when i purchased the boat. The motor just ran flawlessly on the test ride (and still does) so i went against my gut bc of the deal i got on the boat. So im hoping that ive caught the problem in time, will make the repairs and be a okay here in a few weeks. I do appreciate all the knowledge, never hurts to listen!

Sounds like a plan. Just make sure the gasket surfaces are super clean and you'll be good.

 

[Finsleft258]

Anything in particular to look out for while repairing? Seems pretty straight forward.

It is. Roaches and 3-cylinder Yamaha outboards are the only things that remain alive after a nuclear blast.