Gray Case faces - Oxidation or grime

[jtsilverfox]

I'm about to put my crankcase halves back together ('69 911E rebuild), but I'm not sure how the case mating surfaces should look? I've been cleaning everything forever, using various solvents, degreasers, carb & brake cleaners - but my magnesium crankcase mating surfaces are still all a dark gray -- same color as the rest of the case. They have no obvious grease or dirt left on them anymore, but they're not the shiny silver I see in all the photos. If I rub them with a kleenwipe & carb cleaner, I do get a little dark (oxidation?) on the wipe. But the only way to get to the shiny silver, is to sand it with a fine sandpaper. It takes a lot of sanding to just do an inch or 2. Do I have to worry about it and indeed get it to a shiny silver finish - before applying the Loctite 574 sealant? Or, can I just apply the sealant to the surfaces the way they are?
thanks for any thoughts,
cheers,
jt

[Lapkritis]

If the case has been open for awhile then you could have an oxide layer. There is some discretion based condition the surface is in... do you have any pics of the area of concern? I would use a roloc bristle disc (white or yellow) to quickly clean and remove any surface contaminants when you have everything ready to assemble. Sandpaper can make a bit of a mess in an area where extreme cleanliness is desired. If you do try sand, I would recommend wet to minimize dust and clean thoroughly after even using the roloc.

Roloc discs:

Fine : White
Medium: Yellow:
Coarse: Green

[tharbert]

I think what you refer to may be the machined surfaces of cases worked over by machine shops. Mag cases have a tendency to warp when split. It's prevalent enough that most who split the cases have them machined to true the case halves.

I'm not an expert here but if it's clean, I wouldn't worry to much about the color of the surface. As pointed out, polishing, grinding or sanding would indeed expose the case to particulate that could then ruin the engine. And thinking this through, trying to get a shiny surface by sanding or grinding may actually change the tolerances and promote more leaking, maybe?

Good luck!

[tocobill]

Carb cleaner and a soft wire brass brush to clean it up. Be careful not to gouge. I would be hesitant to use a roloc disc on that machined surface. Even though they are plastic the mag is going to be soft. Your prob being a little OCD ... we have all been there. You could also have the case ultrasonically cleaned. I did my 3.6 case at work and it came out spotless compared to the orig alum 3.6 case that went in. Im sure if you saw a pro put one of these together you'd be amazed.

[jtsilverfox]

Thanks guys. After 70+ viewers, and no responses, I was beginning to wonder if no-one loved me, or if it was a dumb question, or just that no-one wanted to venture an opinion...

I did try some 220 grit sandpaper in a couple spots, but that stuff clogs up after just a few seconds. I've got a roloc-like disk set (from HF). The finest (of 3) brillow-pad types (green) works fairly well also (rougher ones leave bigger scratches).

I haven't had shops do anything other than heads/valves and cams. So I've been trying to clean everything by scraping, parts cleaner/various solvents & degreasers, brake/carb cleaners

I've got a bazzilion photos of my whole process to-date (I hope to post it one of these days - but there's so much to do...

BTW: How do you include a photo into a reply? When I click on 'Insert Image', it asks for a URL. If I copy/paste the path to my photo, a small box shows up at the beginning of my reply. Is that it? Do I just drag and drop it where I want and add any other typing above or below it? And then do additional ones the same way? Sorry if this is covered somewhere else...
thanks,
cheers,
jt

[jtsilverfox]

Oops. Sorry. I just went into "Go Advanced" in the reply area, and I see there, that there's a place to upload a photo... Forgot it was there. Hadn't tried it before. Will go try it...
cheers,
jt

[jtsilverfox]

Here's some photos of my case surfaces:

Shot of the right half:


One of the corners sanded a little:


And, after cleaning a lot more in that area:


Lets see how this post looks.
cheers,
jt

[Lapkritis]

Hi JT,

The regular roloc pads without bristles should be avoided. I don't use those anywhere inside an engine. The bristled pads are much, much more delicate on the surface and are far less prone to damaging the surface should you overwork it slightly.