I'm not going to flood the blog with post after post of the cleaning process but just each big step that I do. So this post is about what I've learnt doing the gearbox.
Remove the solid dirt on the engine / gearbox - I used a product called Gunk and some wire wool and a tooth brush and let it sit for 15 - 20mins. Then wiped off what I could. Dont worry if its not perfect you are just removing the majority of what you need to, the dirt staining gets done later.
Wire Brush - I tried varying wire brush methods so I'm just noting the one that worked for me. I used a wire brush set that goes into a drill. The link below is the one I have actually used.
Now it cleans up the metal amazingly and removes the last bits of dirt. Now the down side is if your not careful it can scratch relatively deep and of course it is actually scratching the surfaces to remove the dirt. To get it back smooth and more shiny you could use a mop to polish it.
I wont be doing this I just want it clean and will clear laquer it to protect it for the future.
Tip - By pushing the wire brush over the top of the nuts gets rid of any slight rust on them and they look like new on the gearbox as shown in the pic below. To get like the below I have spent around 6hrs cleaning that bit so far....many more hours to go and still a a little bit in some of the areas ive done.