I've been reading builds from the site and noticed that some of the build sheets had head gaskets .030 bigger than the actual cylinder bore. One guy had a bore of 4.125 but a 4.155 head gasket. Any reasoning for this? I'm new to this so I'm no engine builder. Thanks. Just trying to learn

 

I'm going to guess to account for either gasket swell, or the clearance around the bolt holes, or whatever datums the gasket to the block.

3 hundredths of an inch is going to affect the sealing properties of the gasket and keeping oil and coolant and combustion gasses where they should be and not where they shouldn't be by no noticeable amount.

 

0.020-0.030" oversized is standard practice. My cometics are 0.020". Remember that's diametric, so radial clearance is half of that. You don't want the head gasket in the combustion chamber, so having it slightly oversized gives you some margin, since there are tolerances on everything (head dowel location, etc).

 

Thanks guys I appreciate it. Now I can get some head gaskets on the way ☺