How to keep the gloss in the polished aluminium

  • Thread starter Thread starter Erivaj
  • Start date Start date
Laverdalothar said:
Davo said:
Has anyone tried any of the DIY clearcoats available, or even clear powdercoat?
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yes - all the japs from the 70's had clear coat on their polished alloy parts. Result: a stone hits it, the coat cracks and water brakes in. The alloy corrodes and you can't polish it away. No fun.
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Isn't there a high zinc content under the clear coated ally on Jap bikes..which goes right poxy when it corrodes ?
 
Hi Joe

I don't know to be honest. But what would be different if not? Point is, that if you clear-coat the alloy, any stone flying around will crack the coat, potentially down to the alloy. What happens then is that the alloy is not protected anymore and it starts to corrode, too. No?

The only way I see it POTENTIALLY be less affected is if you steel-ball-blast (right word?) the alloy with small balls made out of steel. Rims are treated that way if they schall stay shiny and on the it seams to work (basically compresses the surface and makes it much harder for water to get in and "brake open" the structure so it corrodes less I am told). Not sure though this works on thin engine covers like ours?!?!

I did not read through all of the content, but whom ever it may be of interest to, here are some deep information about alloy finishing:

http://books.google.de/books?id=Lskj5k3PSIcC&pg=PA452&lpg=PA452&dq=steel+ball+blasting+alloy&source=bl&ots=FsF2fg7DkW&sig=Of64hJETs02xvqgbqOLe03Br8bE&hl=de&ei=odI-TaeEM9KBswbCxe3bBA&sa=X&oi=book_result&ct=result&resnum=4&sqi=2&ved=0CDwQ6AEwAw#v=onepage&q&f=false
 
The Zinc is to get the correct properties in the alloy for pressure diecasting. This is a cheaper process than sand casting.

My old Beemer has sand cast fork sliders and engine casings. I went for a ride in very cold conditions a few years back and the bike got back late at night plastered in wet salty water. I put the bike in my friends garage for a week and when I returned to retrieve she was looking like frosty the snowman ..More salt than Sifta Sam !

It took five washes with cold water to get the salt off and I was still finding salt crystals in nooks and crannies way into the summer.

There was no pitting ..and no discoloration of the aluminium  parts at all. None. I had no wax or AC50 treatment on the metal parts at all.

Quality !

The zinc whilst it improves the ductility of the mix allowing very light and precise castings at a low unit cost..tends to go black and manky

I haven't taken the Jota out in very salty conditions but she has seen NaCl without any great problems. I don't think the casings are pressure die cast. I'd be very surprised if they were ?

 
Laverdalothar said:
Davo said:
Has anyone tried any of the DIY clearcoats available, or even clear powdercoat?
Click to expand...

yes - all the japs from the 70's had clear coat on their polished alloy parts. Result: a stone hits it, the coat cracks and water brakes in. The alloy corrodes and you can't polish it away. No fun.
Click to expand...

Hi Lothar and Davo

my present 70's Kawasaki rebuild had clear coat of the engine casings and forks. Had turned ugly yellow with whitish corrosion underneath. I used paint stripper to remove all the clear. I can report that after sanding then polishing with coarse then medium everything came up mirror bright. I then gave everything a good coat of wax, looks great. To keep it shiny over time will require periodic repolishing and rewaxing as normal maintenance. You can see the final result on the forks in the "1978 was a good year" thread, I posted a few Kawa rebuild photos today.

Paul LeClair
 
The reason I ask re coatings is there appear to be quite a variety used and discussed on the American hot rod sites, used especially for coating bright polished engine parts. But hey, my 3cl fork legs came up quite bright with just a simple wipe over with an oily rag after sitting in a shed for 15 years so ...
 
Are Laverda engine casings sand cast ? I have read that the alloy used is an aircraft specification and although it will lightly oxidize at the surface this soon polishes off without pitting like the Jap zinc diecast.

My guess is that they are sand cast but I don't know for sure
 
The outer covers are die castings, not sure how they did the crankcases. I've welded most Laverda outer covers sucessfully but you get the odd one especialy on the later bikes that is a bit too zincy to weld nice so there is obviously variation in the alloy formula.



    Keith.
 
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