Cleanup of mating surfaces...
 

I am about to reinstall a completely cleaned up intake manifold (1989 560 SEL). I noticed a lot of residue on the mating surfaces of the cylinder heads.

My plan for now to cleaning this up is using acetone as a solvent, but I am looking forward to any other suggestions. What have others done before bolting the manifold back in with the new gaskets?

What's the residue? If it's old gasket material, soaking with Permatex Gasket Remover and then using a plastic scraper (sometimes a few soak-and-scrape cycles if there's a lot of material) often works wonders.
Permatex® Gasket Remover

Thank you!
 

Yes, it does seem to be old gasket remains. I will follow your advice. Thanks!

The Permatex Gasket Remover won't melt silicone / RTV, but it works well on old-school paper and solvent-based sealers. If you can find a can of the old (high VOC) Permatex spray, it probably works even better than the new low-VOC stuff. https://youtu.be/iF2my-oganM

In that case acetone migh be the right answer after all
 

I think I will be scrubbing there for a while...:evilgrin:

I recently bought a carbide scraper, it is simply amazing, just drag it on the surface and the gasket debris simply peels away with it. Finish off with a solvent cleanup, cuts time by as much as 10x.

^ Great tip for steel or iron parts! Just don't use a carbide or steel scraper on aluminum, it's too easy to damage the machined surface.

Sometimes a slightly dulled putty knife would work. A perfectly sharp one may gouge into the aluminum.

Finish with a scotchbrite pad.

This is the one I bought

Scraping Tool | Super Scraper | Carbide Processors

Just lay it on the aluminium surface and pull towards yourself, it lifts out any gasket, then finish with a solvent or if fine polishing is required a silicon carbide sponge of 3000 or 4000 grit can make it shiny as a mirror. A soft brass brush is also a good tool to finish off as it doesnt change the surface characteristics of the item being worked on.

Of course proper common sense is required when using.

Before this I used to use smashed copper pipe to act like a scraper, its soft, but takes longer. In half cases I still have to use the copper pipes - when the area is very small

scotchbrite is very bad on an engine surface unless you are going to flush the object clean with cleaning surfactants.

That's a really nice tool, and pulling (instead of pushing) makes it less likely that the surface will be gouged. Bookmarked!

I've got very thin residue, it will not scrape off, I've tried a plastic scraper. It is super thin. Unfortunately, the Permatex gasket remover is pretty useless against this stuff, and the acetone takes a lot of effort too. Any other chemical suggestions?

Or should I just leave it and pray the new gasket will seal over the old residue?

find a scrapped copper pipe and smash it to an edge, then sharpen it a bit - use that to scrape it. Copper is a bit softer and wont hurt the aluminum if you are sort of gentle on it.

Never tried one, but brass scrapers and putty knives are available. Looks like copper and brass are similar in hardness, with copper being a bit softer.