Trying to finish 5.0 timing job, engine not rotating smoothly

[SailLaser]

Ethanol blended fuels.

I have access to no-ethanol marine fuel at stations but my understanding is that modern high compression ratio engines are more at risk from damage due to knocks from the the lower octane no-ethanol fuel than what the ethanol does to the engine... but I could be wrong.

 

[SailLaser]

Corrosion probably dropped down on top of the pistons and fell between the piston and cylinder wall and on top of the rings while cleaning it. I would have left it or removed the heads and cleaned the corrosion off on a bench because now there is potential for premature ring seal failure later on in life.

Agreed, I didn't like closing it up like that. I spent around 4 hours vacuuming and inspecting but I know there's no way I could have gotten it all. I don't know when I should check, but after running it for some time, I will check that the scoring isn't changing or increasing drastically. Considering it's milage and what I've read, I figure there might be a reason to remove the heads in the not so distant future anyway...