The
Tech Service Bulletin 00-06-01-012J is worth a read
GM does not recommend abrasive methods to clean gasket surfaes, especially since the abrasive grit makes its way between the piston and cylinger walls and then into the engine. According to GM, abrasive materials left behind (from scotchbrite pads or surface conditioning disks) can cause premature bearing failure in as little as 2,200kms
GM recommends using a razor blades or plastic gasket scrapers, or
GM low VOC gasket cleaner p/n: 88900163 (brake part cleaner). Obviously they expect you don't gouge the deck
Having said that, I've got an OCD method I use. I turn the engine so pistons are not at the top of the block. Then use a lint free cloths to wipe the cylinder bore to piston junction before appling a wedge of grease around tha perifery of that area to stop/minimise crud getting between these components. When I've done it, I then very carefully clean the block deck using blade followed by an abrasive scotchbrite pad (yes not ideal). Obviously one tries to avoid gouging the deck with the blade or focus on one spot too long with a pad, but generally such isn't a problem on the few iron blocks I've done.. Sadly with alloy blocks, stuff happens... After the scrap and rub, I then carefully wipe the deck and bores using cloth. I spray the cloth with cleaner and when wiping i stay away from the grease wedge. I finally take away the grease wedge using a right angle plastic scraper and a cutting action before wiping reminants way using another clean cloth while trying not to push grease & crud down between piston and cylinder wall while wiping. It's served me ok but doing such on an old school unstressed iron block 4 cylinder is different to more modern alloy block V8.
I've always thought i'd make a bore plug (
similar to this) that i could use above the piston to supplament the grease wedge (to be sure to be sure). But just didn't do so much engine work and never got around to it.
So it you start sanding the deck, just be carefull where the grit ends up cause grit, oil and bearings don't make great bedfellows.
PS: here's
another persons method which aint hugely different to what i've done in the past (and again it looks like iron block) ... And
another thread that contains comments about abrasive getting to where is shouldn't...