Mystery metal

[gdh12bike]

Hi,
Anybody know what the material is that is used for the GT550 engine case covers?
I thought it was aluminum until I used aluminum cleaner on it and I ended up with a smutty mess. - Gary

[Coyote]

Before you polish, you must remove the clear coat with paint stripper and elbow grease. The cases are made from a low grade aluminum, but they do polish out nicely

[gdh12bike]

I had removed the coating, but the Al cleaner left a load of smut. The stuff worked great on all other Al I tried it on - came out clean and bright...

[oldjapanesebikes]

As Coyote says - it will clean up nicely, but does take a bit of work usually. I use 0000 steel wool and (insert the name of whatever your favourite metal polish is here).

[Jughead]

I use Aluminum Cleaner on my Case covers too.It does turn them Black and Etch the surface.I've found that it helps to get rid of some Imperfections before Buffing.

[gdh12bike]

That's why I’m not convinced they are aluminum. Everything else aluminum I used that cleaner on came out bright and clean. I wet sanded mine - they were so bad, and then buffed them... They now look good, but waaay too much work!

[tz375]

Pictures? Sounds like the covers still have some clear coat on them. How did they looks after hitting them with wet and dry?

[Jughead]

Rest assured they are aluminum.The Alloy the Aluminum cleaner your using is Probably made for is Billet and/or Cast Aluminum Wheels.From my experience from playing with different parts that I've tried to clean using the Aluminum cleaner,Original Carburetors from the Suzuki's faired the Worst.Before Realizing those were made from Zinc I did just about Dissolve a set from my first T500.Being as How the covers Turn Black and have Smut come off of them they are an Aluminum Alloy containing High amounts of Zinc.
I don't know how Japan Rated the Alloys that they used back then compared to today.(I'm not a Metallurgist or rocket Scientist by any means)(More like a Half Smart Back woods Hick. ) BUT I'm thinking they Just experimented with Different Mixtures of Metals until they came up with something that worked Very well and they stuck with it.I'm sure they Used Zinc Because it was Readily Available and since it is a Softer Metal than Aluminum they Used it as a (Free Flowing Agent) in the casting process.

[oldjapanesebikes]

The stuff is called 'alloy' for a reason I would expect they went with whatever combination of aluminium and other metals that gave them the best per unit cost, and lowest rate of rejects in a mass production environment.

[gdh12bike]

Ahh, the zinc in the alloy would defiantly explain it. I used to work in the aviation business where we did chemical milling of Ti and Al. Smut could be removed with something called, "Smut Go", and it always worked on those parts, but I never tried it on junkier alloys. I bet that is what is in the Al cleaner we are using.

Pics to follow..

[H2RICK]

The factory bought castings from outside suppliers, of whom there were/are many in Japan.
IIRC, the engine covers would have had ~7%-10% of zinc mixed in to give the pieces some rigidity.

Conversely, most mass produced carb bodies are zinc die castings with about 7% aluminum added to give the finished casting some flexibility. Zinc is very strong....but brittle. The aluminum reduces the brittleness so that the casting can be machined without fear of shattering.

The proportions of the metals can, of course, be varied to suit a particular application but the proportions I've mentioned above are quite common in the vintages of bikes we're dealing with.

[Suzsmokeyallan]

I swear one day I'm going to polish a cover and be able to read some label in it like Pepsi or Coke on a part of it somewhere. The covers were of such an impure material you can see flow lines and such in a matrix of varying colours in many of them.
Aluminum yes, zinc yes, and some other suitable cans and scrap thrown in to add mass and help cut costs, thats why they are so heavy.

[Coyote]

The black 'smut' that occurs when polishing, wipes off clean with plain old lacquer thinner.

[H2RICK]

be able to read some label in it like Pepsi or Coke on a part of it somewhere.

I wonder even at the "late" date of our GT's the labels might read
Nakajima, Mitsubishi and Kawanishi instead ???