I always hate how it takes 2+ hours to clean head gasket residue off a block, so I took the advice of an auto parts store manager and tried those little abrasive disks that you can spin with a drill.
Things were going fine until I scratched the top of the cast iron sleeve.
The small scratch ran out from the cylinder toward the cooling jacket so I knew the solid metal ring on the head gasket wouldn't seal it. By the time I had polished it out with 400 grit sandpaper, I had taken .002 inch off that spot (as measured with a straight edge). The tip of the screwdriver points to the spot.
I was too nervous about the new head gasket sealing this "divot" so I decided to play it safe and get it flat. I had to strip the block and take it in to the machine shop to get the deck refinished.
So, just take your time and spend the 2 hours scraping the head gasket residue off with a razor blade and maybe a little steel wool. Otherwise, you might spend an extra 4-6 hours and an extra $50 to get the block machined. Thankfully I already had this block out on an engine stand when I messed it up.
Another issue that I have read about (after the fact) is the abrasive grit that these pads will leave behind in your cylinders.
Moral- shortcuts can waste lots of time
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