SOHC.co.uk Forums > CB500/550

Was front forks originally painted?

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AshimotoK0:
Here you go Ken ...clear chromate conversion coating ... like Vic World uses

I can't just sand a fork leg  'cos  all of my forks here I stripped and polished years ago. I think I have some 1969 forks off a 5k mile  CB250SS at my stash though .. so next time I go there I will dig 'em out. From memory the lacquer was still on and in pretty good nick.

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Oddjob:
Perhaps Vic Worlds does use the coating, doesn’t mean Honda did though Ash. Maybe they couldn’t find the exact colour that Honda used and that gave a close enough result.

I can’t see that word Hexavalent Chromium without thinking of Erin Brockovich

AshimotoK0:

--- Quote from: Oddjob on March 19, 2022, 02:55:00 AM ---Perhaps Vic Worlds does use the coating, doesn’t mean Honda did though Ash. Maybe they couldn’t find the exact colour that Honda used and that gave a close enough result.

I can’t see that word Hexavalent Chromium without thinking of Erin Brockovich

--- End quote ---

It's generally accepted, particularly in the aerospace industry that normal paint/lacquer will not adhere reliably to aluminium because of the oxide layer that immediately forms on bare metal. Honda were pretty advanced and probably used a lot of ideas from other industries. If you sand back a CB250K frame you will not find any evidence of a solvent based  primer but a definite light grey coating which I guess may have been some form of phosphate etching or other metal prep chemical process.

If Honda basically 'painted in' the pits in the alloy, why is everyone on these forums sanding the hell out the original finish to get a uniform satin surface like the showroom finish (or highly polished ..yuk). why not just spray the pitted alloy  with a can of Duplicolor DE1615, flatting off and then lacquering? 

I think hexavalent chromium chemicals are pretty much outlawed everywhere now .. although I suspect and know of at least one chromer who stockpiled enough of the stuff for 'special jobs' to see him into his retirement.   But back in the day Honda or their sub-contractors, would have readily used the stuff along with cyanide in the zinc plating and asbestos in the gaskets, brake linings etc.

Maybe I have been lucky Ken and had fork bottoms that were decent enough, with no surface imperfections, that they were never painted to hide the pits but I am still of the belief that non of them had any silver paint applied (talking Honda CB250k's and Honda 4's here  .... Most of my 60's bikes were definitely painted finish when they left the factory, apart from my 175 sloper.

K2-K6:
I can't see that it's painted either. The grey as far as I'm aware comes from the chromate process inhibiting the natural corrosion from taking place within the outer layer of the casting.
It doesn't last for ever though effectively being sacrificial in protecting the bulk of the casting, it ultimately turns grey and prevents propagation through further into the material if left alone.
If significantly breached, the casting then starts to go furry as most raw aluminium does if not ultimately protected.

Oddjob:
Well whatever it is it's something between the lacquer and the alloy. That's essentially my point, all those people who kept saying it's polished alloy just lacquered are incorrect, it's not and never has been.

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