Polishing Aluminum

Bonwit · Oct 29, 2009

I'm in the process of polishing out an old primary cover I bought at a rally a few weeks ago. It was pretty tarnished, but not too many gouges. I started with 60 grit and was able to remove the deep scratches and gouges. Following up with 80, 120, 220, 400, 800, 1000, 2000 and then a rag wheel with compound left the cover with a bright finish I can see myself in. However, if I reflect off a bright light, I can see some tiny pitting in the surface, not large enough to feel with a fingernail, but enough to make it just short of a true mirror finish. Mounted on the bike, and particularly after riding it a week, I'm not sure one would notice.

My question is, is this cover able to be shined to an absolute mirror finish, or is this alloy not capable of that level of finish? I worked like hell with the courser grade sandpaper and would have thought that would have removed these tiny imperfections. Am I asking too much?

Any ideas?

kommando · Oct 29, 2009

You may have porosity in the casting, as you get rid of one set of spots you reveal a new set so leave it as it is or you will be left with nothing. Norton castings seem to sufeer more than most from prposity, maybe it was the lower volumes or a different alloy.

Flo · Oct 29, 2009

My old Primary casing was alright, until my rotor nut flew through it. Bought a brand new one, only last year & it has minute black holes in it like what you mention.

pelican · Oct 29, 2009

It's normal to have the pitting as it's a casting flaw. CNW polished all my stuff a few weeks ago. Some stuff looks amazing and some not so much, but they said that's normal.

Paul · Oct 29, 2009

Talking about polishing: at the "De Brug" meeting of classic motorbikes in Leuven recently (yes, where Yvesnorton won an award with his beautiful Norton Seeley ) - see his posts:
norton-seeley-t4799.html
there was a guy (Luc Meermans) who has become really famous in Belgium and surroundings with his astonishing restorations.
The bike he showed at this event was a Gilera. How much time he spent in polishing the aluminum can't be overestimated I guess, but look for yourself at the pictures below.

Scooter62 · Oct 29, 2009

Flo said:
Bought a brand new one, only last year & it has minute black holes in it like what you mention.

Thanks Flo, you saved me $300. I was about to purchase a new outer primary, thinking by now they would have figured out how to cast the bloody things without including all the garbage. If the new ones have the same problems It's a waste of money. Can't understand it though since the timing cover polished up a treat.

Scooter
"What you own, owns you"

swooshdave · Oct 29, 2009

Scooter62 said:
If the new ones have the same problems It's a waste of money. Can't understand it though since the timing cover polished up a treat.

It probably has to do with the size of the casting. A small casting such as the timing cover is easier to make with fewer blemishes. The larger primary cover is tricker due to the size which make pouring and cooling more challenging. At least that's one guess.

Cookie · Oct 29, 2009

I'd wonder if a guy might do better by going for the earlier casting where they fit? I don't go for the mirror finish anyway myself as I think a bike with a bit of use looks better.

gtsun · Oct 29, 2009

I think you just need more practice so in the interest of being a good person & helping my fellow man I'm sending you all the alloy bits from both my bikes! After you polish & return them I'll send you some stainless stuff. It's even harder to do so you should be an expert by the time my bikes are done & gleeming!!!

DogT · Oct 29, 2009

I find that I can, if I have to, start with a bastard file to get the gouges out, go right to 100 or 150 with a hand sander, go right to 220 or better 320 with the sander and then the black compound with a buffer will take out the sanding marks with some aggressive buffing. With Aluminum, I use then brown and then on to white buffing compounds. With steel I find I can go right from the black to the white compound. As far as the small pits in the AL, you will never get rid of them on the Norton primary, gearbox cover forks, timing cover, etc. they are hateful little holes. This is about as good as I can get it.

I have seen Simichrome make aluminum look real good too.

Dave
69 S project

seaguy · Oct 29, 2009

After you get it all done I have found that Mother's AL polish Keeps it shiny for a while. Then when you polish with it you really get the black stuff so it looks better and better with each session.

T.C. · Oct 29, 2009

+1 on the Mothers' Aluminum Polish! I used to swear by Simichrome, and I still like it for chrome & stainless, but the Mother's will bring the cast aluminum "brighter" than the Simichrome will. Don't use the same polishing or buffing cloth for both, though.

Those tiny pits are either porosity or tiny inclusions of foreign materials. f you have them on the surface of a casting, they're probably all the way thru the casting. Ditto what kommado said on that, you'll polish the castings to nothing before you get rid of them. They're just part of the Norton personality.
Make it look as nice as your patience will allow and your eyes will accept.

bpatton · Oct 29, 2009

A guy that owned a chrome shop told me that polishing alloy involved more than cutting the surface to level. The final stages are a burnishing where the top layer is actually smeared into itself. It's why the bearings on commercial buffers are rated higher than a benchgrinder and the guys that use them are often XXlarge.

Bonwit · Oct 29, 2009

This is just what I wanted to hear. I think it looks pretty darn good, but I didn't want to waste my time going for perfection that was unobtainable.

This is truly a GREAT forum! Thanks.

tpeever · Oct 29, 2009

T.C. said:
+1 on the Mothers' Aluminum Polish! I used to swear by Simichrome, and I still like it for chrome & stainless, but the Mother's will bring the cast aluminum "brighter" than the Simichrome will. Don't use the same polishing or buffing cloth for both, though.

Autosol is much better than Mothers. Also seems to protect better.

RennieK · Oct 30, 2009

Bonwit said:
This is just what I wanted to hear. I think it looks pretty darn good, but I didn't want to waste my time going for perfection that was unobtainable.

This is truly a GREAT forum! Thanks.

I think the bottom line is once you've done all the pieces as best you can and have them on the bike it will look fantastic. No one will notice these tiny imperfections on a complete bike.

Here's some good info on buffing and a downloadable guide: http://www.caswellplating.com/buffs/buffman.htm

maylar · Oct 30, 2009

A real labor of love, isn't it? Aluminum looks so magnificent polished, too bad it doesn't last. I, too get those little black spots but believe me nobody notices.

When parts come off my bike they get touched up with the buffer. On the bike it's either Mothers or Autosol. Mothers is better at cleaning water spots, Autosol shines a bit better.

My homemade buffing station:

This is what the buffer gets you:

grandpaul · Oct 30, 2009

Brilliant! (literally)

Bonwit · Oct 30, 2009

RennieK said:
I think the bottom line is once you've done all the pieces as best you can and have them on the bike it will look fantastic. No one will notice these tiny imperfections on a complete bike.

Here's some good info on buffing and a downloadable guide: http://www.caswellplating.com/buffs/buffman.htm

Hey RennieK, This is a great site! Tons of info, and the forum contains lots of hints pertaining to motorcycle polishing. Thanks!

DogT · Oct 30, 2009

You can get a decent 3/4HP buffer at Harbor Freight for about 80USD delevered. Get the buffing wheels and compounds at Caswell's. Here is a shot of my before and after of the timing cover.

I have also been using Copy chrome on a lot of the specialty parts and it looks just like chrome with only one plating process. Don't know how it is going to hold up though.

Dave
69 S project

Polishing Aluminum

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