SAE 3 ZF 220A Adapter Plate sweating rust?

[Alex]

Hi everyone, Happy new year!

Ok this is a weird one.

Rebuilt 6BTA sitting in garage, covered in plastic to keep dust out and an additional drop cloth over it.

The original adapter plate for the ZF 220A was completely stripped of paint and primer, wire brushed, ospho, heated with a torch to drive “moisture” out prior to new primer and two-part urethane coat.

All through this process I noticed that it was weeping drops of rusty moisture in several spots to which I took a dremel carbide bit to clean out to bare metal (again) and primed and spot painted.

Now months after the last treatment to stop the rust its evident that under the primer and paint its bubbling rust again, creating like scabs of rust under the paint that I can scrape off and rust flake would appear.

Before rebuilding the engines, that stb plate had severe surface rust due to leaking fish box that dripped over the bellhousing + neglect.

Structurally these adapter plates are sound, and the port side one is not showing this issue as it was not rusted as the stb one was before I got it.

Before disassembling, having it sand blasted and trying again…. Any ideas why this cast iron or cast steel (not sure which is) keeps sweating or weeping moisture from inside the grain structure even after all that treatment?

All this is happening in the garage! not installed in the boat.

Thanks!

Topic

[Alex]

Photos

See attached photos of rust scabs

[Alex]

Hi Tony, Not that I had noticed on any of the bronze thruhulls. They all looked clean, just the dull bronze color that is expected, no black tinge, coating and no pink or green corrosion.

Its almost as if the cast adapter plate soaked in moisture to a degree that no matter how much I cleaned and dried it keeps bubbling out over time.

This rust is only on the outside/rear surface of the adapter plate, the inside towards the flywheel looks new with zero rust.

I will take some photos of the plate in question and scrape one of the scabs off for you to see.

 

[Tony Athens]

Any of the brass or bronze  in the  engine room showing any signs of  a black tinge or coating?  Look closely

Seaboard Founder & President

[Author]

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