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#10150
BRIAN MARSHALL
Participant

Hi,
Powder coating will not really cover pitting, and you cannot fill with a non-metallic substance and then powder coat. There are techniques used by the non-destructive testing folk, mainly in the aviation industry, to check for internal corrosion, but it is very expensive to have done. My cousin was recently obliged to have it done on the wing struts of his 1941 Taylorcraft light aircraft, following a couple of fatal crashes in the USA where the struts failed due to hidden internal rusting caused by water ingress.
In the vintage motorcycle world the only items that would really bother me personally are Druid, and some other makes, of front forks, as they were made from thin gauge tubing, and nasty accidents have occurred when they have suddenly failed. You really need to get expert advice if the external pitting is serious. NEVER, EVER, draw-file the tubes to remove the pitting !!
If you are happy with the integrity of your frame, after gentle sand blasting to reveal all the pitting, I would then give it a couple of coats of red oxide primer, then fill visible imperfections with a car body type epoxy filler, rub down to a smooth finish, prime again, because the rubbing-down inevitably exposes areas of bare metal, and then paint with a finish that is compatible with your primer. Do check with your paint supplier that the paint is petrol-with-ethanol resistant.
The various finishes available have their pros and cons, and you should consider the use the bike is going to get, as some finishes are nice and shiny but rather brittle and prone to chipping. Cellulose on the other hand is rather soft, but it is very easy to touch up if chipped, and can be ‘cut back’ with a rubbing compound to restore its shine and remove surface scratches.
Hope this helps!
Brian