Oxalis acid is used for many things including neutralising rust. I bought a small amount last year to help clean rust stains off the sails which didn’t work very well.
Here however I used it on the bits of the engine mountings that I salvaged. They were caked in thick loose and flaking rust.
Three days in a tub of acid and look what happens. Apart from going a rather disgusting green colour the rust has all but disappeared.
The piece that is still soaking has had one end treated.
Pretty good and now ready for painting.