Can you polish mag caes like Alloy one's

[David Lahey]

I usually use etch primer then automotive touch-up spray paint on motorbike "magnesium" and have never had a problem with corrosion or the paint falling off.
If you have made something metallic very shiny and now want to paint it, the paint will stick better if you give the surface some roughness (fine sanding is good) for the paint to hold on to.

[DR]

jeez I wish it wasn't 2am cause I'd whip down and take photos of my rm400 and tm125 covers as they sit. Both have been through all the recent shit weather and bullshit of late and have not been touched since CD7 last year. The RM cover is dull and need a quick polish but 'no' corrosion whatsoever and the TM cover looks like I've only just polished it yesterday as it's still gleaming. I just checked to be doubly sure! The only corrosion I'm having is the white oxide on the polished 'alloy' cases from the damp weather of late. I would not hesitate to polish more.

late edit, just snuck a photo of the TM cover As you can see the metal parts on the RM beside have started to corrode with the damp weather of late but the mag cover is just dusty and still quite okay...

[GMC]

Sorry, I guess I got to technical. I wasn’t suggesting that it couldn’t be painted or that it would disintegrate in your hands.
It will just be affected long term, depending on conditions.

"Magnesium" is actually an alloy of magnesium and aluminium (and other stuff) - bikes don't use anything like pure Mg, just like they don't use anything like pure Al.

Exactly.

Also the amount of various elements in a casting varies from manufactures and years.
Generally high Mag content is a bit more greyish in looks and I wouldn’t have thought would polish to the same shine as your average alloy.
The tarnishing is actually the oxides forming.

[Slakewell]

Normally the lighter it is the more Mag in the casting. You can also give it a file and see how hard it is.
Ill give it a buff and see and post some photo's.I will also paint clear afterwards if it looks OK. 

[GMC]

Normally the lighter it is the more Mag in the casting.

Yes, and also more brittle.

[Slakewell]

Yup easy to smash. I used to hate welding chain saw cases so charged like a cranky bull 

[firko]

I'm about to have these magnesium Morris wheels prepped and powdercoated. They're intended for my 650 Benelli flat track project. The front's in pretty good nick but the rear, shown is covered in peeling powdercoat and shows some powdery oxidation. This is the first I've heard about it being detrimental to blast magnesium. Can anyone enlarge on this before I do something I may later regret?

[Davey Crocket]

I didnt think TM's had any mag parts on them Doc.......arent they just alloy?

[Lozza]

I know the magnesium wheels have to be sealed with something or rather otherwise they leak air.

[montynut]

Firko,
You should really have the wheel x-rayed or some other NDT as all true Mag Alloy wheels do have a use by date. CAMS require bi-annual tests of true Mag Alloy wheels as far as I know. When Alfa fitted true Mag wheels to road cars they caused all sorts of problems as the coating was easily damaged during tyre changing by the local service centres using normal tools. Morris are arguably the best era wheels unfortunately the alloy deteriorates internally nothing to do with the wheel manufacturer.

The flywheel cover on Montesa Cota 349’s is Mag Alloy and is feather weight for the size of the cover. I have found that if not coated the alloy deteriorates rapidly actually becoming brittle and is attached internally by the environment not just on the surface.