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Message: <blockquote data-quote="96blak54" data-source="post: 1412085" data-attributes="member: 14727">If he doesnt send the block out for machining.Suggested prep. Ensure surface is true by take a straight edge and shims to find untrue planer spots. Most times these areas are between bores. Cast iron blocks can be around .001-.002 while aluminum can tolerate up to .005.Aluminums expansion continuous moving properties is why .005 is acceptable. BUY...if it were my money spending, id be 100% sure the block deck was flat.Now about taking a razorblade...adding a scratchy surface. Alot of folks like to use scotchbrite in surface preparation. Not a good idea. Cleaning, yes. Scotchbrite reduces or eliminates the desired surface roughness needed for a gasket to adhere to. Smooth is not what you want. The surface needs peaks and valleys in bedded with in like 400 grit sandpapper would do, but we dont want "sand" anywhere near the engine...bad idea. So use a razorblade on its sharp edge and apply scratching to the surface. Not deep scratches, but noticeable imperfections. Not really a scratch your fingernail can drag on either. I qoute "the proper machined surface roughness is idea". But if youre like me pinching pennies, you find away. After cleaning the block surface, youll have reduced the original roughness. This is where the scratching comes in.Having the proper peaks and valleys, better know as surface roughness, allows the head gasket to securely adhere. A smoother surface and the outer contact of the headgasket wouldnt mate properly.</blockquote>