Reassembly: Surface Preparation

Back in the day when cylinder heads and blocks were cast iron, cleaning sealing surfaces was a lot easier.  Grab the ol' metal scraper and the air grinder with some abrasive clean up disc and have at it.  Times have changed; everything is made out of aluminum.  Plus coated metal gaskets are pretty common instead of thick composite gaskets.  Get too aggressive with a metal scraper and you can wind up with deep scratches.  Abrasive discs can quickly cut shallow divots in aluminum gasket surfaces that are barely visible but can make it impossible to get a metal gasket to conform and seal . Another concern with abrasive discs is the disc residue.  The residue contains bits of abrasive material which could get blown into the engine assembly leading to oil contamination, internal component failure, and severe engine damage.  Meticulous preparation to keep material out of the engine as well as post clean up is mandatory if you even think of using abrasive discs.

A good method I've found for surface cleaning is to first soften sealant residue and loosen old gasket material with solvent.  Yamalube Brake and Contact Cleaner works well.  Follow up with a plastic scraper to remove the stubborn stuff.  I have tried lots of different plastic scrapers, store bought and homemade, over the years with so-so results.  A few years ago I discovered a plastic scraper from Snap-on that works great.  These scrapers, make of NYROC, were orginially developed for removing difficult materials from delicate and easily scratched aircraft fuel tanks and fuselages.  These scrapers are hard enough to hold a sharp edge for removing sealers and gasket material while not scratching aluminum gasket surfaces.  I've also used them with good results to remove stickers from painted surfaces, fiberglass, and plastic parts.  When they do get dull they can easily be sharpened with a few swipes over sandpaper. 

Incorrect handling and storage of parts, particularly heavier items such as blocks and cylinder heads, can also lead to sealing surface damage.  Take care not to damage sealing surfaces by sliding or dropping parts against one another or onto hard surfaces.  Protect work surfaces with rubber mats or wood.  Plywood or tempered Masonite hardboard works well and is easy to find.  I particularly like 1/8" hardboard to cover my work areas as it does not splinter nor absorb oil as quickly as plywood.  Also, it is hard enough that gritty debris does not easily embed in the surface, like it does in plywood, which could scratch parts.  Plus, it is relatively inexpensive for 4' x 8' sheets that can easily be cut to size.