Polishing resulted in this...

[Finnigan]

Did the job as I usually do in the past with decent results but tonight was a little different. 2000grit paper and then brown to white rouge on different and appropriate wheels. I noticed a discoloration UNDER the shine that wasn't there after sanding...any thoughts what cause this? Edit: it looks like the coloration nearly frames the HONDA logo in an accurate enough rectangle

 

[doc_rot]

I spun off the kawasaki logos off the ignition cover and stator cover on a kz1000, after polishing there is a similar result where the old logo was. I assume it has to do with density variation from the casting process.

 

[Finnigan]

Interesting, could it be heating up to the point where it 'burns'? Since the cover is very thin everywhere except where the logo is

 

[Drey6]

Interesting, could it be heating up to the point where it 'burns'? Since the cover is very thin everywhere except where the logo is

I've wondered this exact thing!

 

[doc_rot]

Its kind of hard to get a photo of since its so faint, but if you look closely you can make out the kawasaki logo and lines that were originally raised on the cover.

Interesting, could it be heating up to the point where it 'burns'? Since the cover is very thin everywhere except where the logo is

Not sure what you mean by "burn" but since aluminum is excellent at conducting heat, just short of welding it I think the piece would get pretty uniformly hot if it was being heated. Cooling is more likely the culprit because you can shock it cold easier and faster. This is just a theory, but my guess is when the aluminum is pored it reacts slightly to the investment, cooling faster on the outside. So the the outside is slightly different in composition and temper, possibly more porous. when you start to sand past this you will notice this unevenness. Sharp edges are usually where casting flash happens; so if there was casting flash around the Honda logo on your cover, the factory would have polished it off, perhaps by only polishing where the flashing was around the logo they sanded through this outside porous layer. Then when you hit it with a polishing compound you are embedding this in the pores showing the difference in density. Mine didn't show up until i used polishing compound.

 

[doc_rot]

Heres what the cover looked like before, you can see the lines and the logo reflected in my polished cover.

 

[VonYinzer]

Did ypu strip the factory coating completely off before polishing?

 

[Finnigan]

Did ypu strip the factory coating completely off before polishing?

Yep, twas a bit&$

 

[johngofast]

I've ran into the same thing. Maybe not a great idea, but I took a torch to the whole area until it was all the same color then sanded and polished again. Worked well for mine.