SOHC.co.uk Forums > CB750
Original Finishes CB750K0 engine PLUS CB500 Four
AshimotoK0:
Just to add to the pot. A Dutch guy on the HondaTwins site added this to one of the posts on alloy finish and he may well be correct.
These are his words not mine:
"For years I tried to restore the original surface finish of the CB72/77 heads. In 2005 I got a NOS head, boxed and in plastic. The surface finish was a zinc layer. This zinc layer is formed during the casting process. The picture shows the original finish, being zinc. This zinc will vanish during the years and the cylinder and head turns dull. It's difficult to restore the zinc layer".
Orcade-Ian:
I've got to say that I had not thought of a thin coat of silver under the lacquer - makes a lot of sense though and is why we can't really replicate it after polishing. As we know, it wasn't that good really and if you rode on salt laden roads just once and didn't rinse it down, then that familiar mottled effect developed by the following day.
As a complete philistine, I have frequently paint stripped NOS parts to remove the lacquer (and now seemingly this silver base coat) preferring just a polished and waxed finish which I find much easier to keep clean. I wonder if anyone knows what silver base was used and if it would still look correct under a more durable 2 pack lacquer.
You've opened a can of worms here Ash - do you know how many flakes of metal per square inch there should be in the paint on my tank?
Ian
ST1100:
So why not simply use Alodine 1001 on the now coat-less, polished aluminium surfaces before clear coating them?
http://na.henkel-adhesives.com/product-search-1554.htm?nodeid=8797999529985
AshimotoK0:
--- Quote from: ST1100 on December 30, 2015, 11:00:54 PM ---So why not simply use Alodine 1001 on the now coat-less, polished aluminium surfaces before clear coating them?
http://na.henkel-adhesives.com/product-search-1554.htm?nodeid=8797999529985
--- End quote ---
Considered it but hard to get hold of in the UK , very expensive and VERY toxic, possibly a carcinogen. Surprisingly though the safety data sheet on the dip you use to passivate zinc plate (very cheap from Gateros plating) states it contains Chromic acid and Hydroflouric acids! I know for a fact that the aerospace industry used Chromate dip to promote adhesion as I think does Vic World the CB750 sandcast guru in the States on the likes of alloy fork sliders etc.
http://gaterosplating.co.uk/Replacement-Items.php
Scroll down to this:-
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AshimotoK0:
Evidently Vic World gave a talk on finishes etc in 2009 in Ohio to the SOOC boys but sadly nobody videoed it (well not to my knowledge). Bet the 'acid' mentioned in the article pic below was Chromic acid.
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WILL INVESTIGATE THE GATEROS SAFETY DATASHEETS . possibly the blue passivate may do the trick. Dunno...will report back .
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