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!

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