Boy, this topic is a one of those proverbial box of spiders isnt it??? (I love that metaphor much better than the US "Can of worms")
As to clear coats, I again agree with Trev for the most part. I have experimented with them and have yet to find one that looked good, lasted a long time and didnt yellow.
There must be some that work, The vintage "Patina" crowd really loves painting over rust and bare metal, I Dont know how they get the clear coatings to stick, but clearly some manage. So it IS possible,, But I have enough problems without going down that route.
I hve some vintage Asian bikes and used to read some crazy ideas on stripping the coatings on vintage Honda SOHC/4 Hondas.. One idea is a oven cleaner foaming cleanser and soak the engine down inside a plastic trash bag and let it sit. Then wipe the coating away or brush it off and then polish. I dont recomend doing that, as it most often attacks the alloy chemically and no polishing will restore it. The alloy will be discolored black-gray ish. Even sanding it down you have to take a lot off to remove the discoloring.
Same with dishwashers... Bad idea in my experience,, but It is possible some variable might work.
What I have used with success on HD and Asian bikes with the deteriorating clear coatings is a mild furniture paint stripper. Something for restoring and refinishing wood. Test it on something you dont care about, But I found a few that will take off the clear coatings and wont attack the alloy, But its a messy job.
I did read some UK Bike magazines like "Bike mechanics" and maybe "Classic Bike" where they took asian engines to a specialist who masked off the engines and baking soda blasted them to remove oxidation and clear coat. Seemed they listed a lot of shops offering the service in the UK. Being the popularity of vintage Asian there...... Ive seen a lot of references to it.
One other option I didnt mention, But will here just to be pedantic... I know a local shop offering plastic media blasting. Instead of glass bead or soda, its tiny plastic balls or chips. Cars with fiberglass or painted plastic you can strip off all the paint, coatings or dirt/oxidation and wont harm the base material.
IE:Corvettes, or other plastic fantastic cars. But it works on sensitive alloy as well. Not cheap but it works really well. Well beyond the home workshop but useful to know about.
See:
http://plasticmediablasting.com/html/automotive.php#prettyPhoto" AUTOMOTIVE
Today there is an alternative to both sandblasting and chemical stripping your automobile. Plastic Media Blasting has quickly become the most popular and excepted method.
Plastic Media is mainly used for thin gauge sheet metals. This method uses plastic granules which are harder than paint but softer than the base material. Using a high-volume, low pressure application, the media will cut, shear and lift the paint without affecting the substrate.
Since it is a dry process, there is no flash rust after stripping and most importantly the plastic won't warp or pit the metal. It's non-corrosive and safe for all metal, stainless steel, fiberglass, plastics, aluminum and moving parts. The only short fall is it won't remove rust... hence may require other blasting methods."
We have a large commercial stripping company in Portland, They can dip entire car and truck bodies in their largest tanks. I have used them for OIF Triumph & BSA Frames (1971-1983) as the one should
NEVER EVER Sand blast, bead blast, or any other abrasive blast an oil vessel. I also used them when people used coatings inside fuel tanks. They can strip out any coating.
See:
However use extreme caution when chem dipping alloy bits, same as dishwashers and other chemicals. I liquidated a big Ariel Sq4 collection and one of the bikes, the owner had sent in some greasy old Ariel cases to the machine shop and they dipped them but used the wrong tank. melted the cases. I have pictures of the results............. this happened in the 1970s and they were able to source some extra engine cases from Nicholson Brothers in Canada with no numbers, But good luck finding replacements today!
This place is who I use locally for chemical dipping and stripping. Mrs Sluggo has her dream car project, Its a 1969 Chevelle muscle car and the whole body will get dipped there next spring. When its stripped to bare metal, they then chem dip it with an acid etch to prevent flash rust on the steel. We can then proceed with body and paint with a totally clean virgin canvas.
This place does not have much of a website, but they do have a lot of pictures on FB.. See:
https://www.facebook.com/AmericanMetalCleaning/My point here is, Dont cut corners, and test your ideas first and do your research.
(Cant find the ariel pix at the moment but here is one polisher/buffer we have here.... What a beasty!)