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Internal marine engine corrosion

Posted: Wed Jan 29, 2020 8:14 pm
by 1911tex
Folks I am a pilot familiar with SEL/MEL apposed air-cooled aviation engines where prescribed annual inspections are mandatory by a certified A&E mechanic. How do you normally inspect a marine engine for internal corrosion without pulling the engine and dropping the pan? Fresh water use only. Case in point, a prewar CC with an original KB engine that was overhauled over 20 years ago and has less than 200 hours? I assume a borescope via the plug opening for cylinder walls/valves...but curious about the crank/cam shafts. Appreciate your advice, this forum is irreplaceable... thanks.

Re: Internal marine engine corrosion

Posted: Thu Jan 30, 2020 8:35 am
by Bilge Rat
You won't get too far with a borescope through the spark plug hole on these flatheads. The plug is pretty much over the deck at the valves, not enough space to sneak the scope into the cylinder unless its real skinny. There is an "inspection" plate on the starboard side of the crankcase, meant for oil pump pressure adjustments. It won't be easy to look around at the crankshaft through there though. The transmission shares the same oil as the engine and you might be able to use a scope to view the aft end of the crankshaft by removing the transmission cover. I guess it depends on how articulate your scope is.

There are valve lash adjustment covers on the port side of the engine under the exhaust manifold. You can see the cam lobes under the solid lifters through there if you remove the covers but again not sure you'll see much without some further disassembly. The carb, linkages and fuel line will make looking in there challenging.

Re: Internal marine engine corrosion

Posted: Thu Jan 30, 2020 8:58 am
by 1911tex
Bilge Rat...thank you, I guess its take a deep breath and hope for the best or pull the engine out, off with the head, and drop the pan....I assume most folks will do the former. Great reply and very much appreciated!

Re: Internal marine engine corrosion

Posted: Fri Jan 31, 2020 6:37 pm
by tkhersom

I am not sure what kind of corrosion you are looking for internally. Any surface rust would be meaningless, and any corrosion on the bearings would not be detectable unless you removed the bearing caps, which would require disassembly anyway.

Having personally performed annual inspections with an FAA issued A&P license (be it many years ago) we never went to that extent and usually only did a cylinder leak down test and visual inspections.

Of course an engine failure in a plane is far more dramatic than in a boat, usually.