Prep Engine Block Deck and Cylinder Head Mating Surfaces for New Gasket

[TWChamp]

I use hardware store bolts, and my Dremel with a small cutoff wheel to grind 4 slots in the last inch of the bolt, then use this to clean out the block thread pockets.

[jpepper]

Taps have a size on them. There is a number on the shank that denotes the amount of pitch line oversize. This is a GH number. Each number step is .0005" . Thread chasing/cleaning taps are usually GH-3 which means they are .0015" oversize. Do not use a tap larger than this for cleaning purposes. Regular taps can be GH-5 or GH-7 depending on the desired thread fit. I used to use GH-14 taps for machining 8620 steel that was going to be case hardened. The holes would shrink during the carburizing process so they had to be tapped oversize prior to heat treat.
here is a link http://www.tapmatic.com/tapping_ques..._h_limits.ydev
You can buy a 5 tap set of cleaning taps from ARP and other companies through Jegs or Summit racing. You might also be able to buy them from McMaster Carr. A basic set is 1/4-20, 5/16-18, 3/8-16, 7/16-14, and 1/2-13. My point in all this is not all taps are the same. Use the correct ones for thread chasing and cleaning so you do not ruin a good block or head.
By the way, I clean the surface with a flat scraper and wipe with Acetone, lacquer thinner, or brake clean.