Whats the thickness of a new unskimmed head,and whats the safe limit of a head to use,i have a sh 4x4 head head that is 138.5mm but i see one advertised at 136mm which i thought was a no no

cheeRS stu

 

Wasnt it 139mm odd from new

136mm deff seems over skimmed?! and only really good for NA use unless piston height is compensated for and probably valve cut outs.

Plus at 136mm would have thought it would have been skimmed right down to the valve seats which could be a problem?!

 

139.12 standard. ford say throw away at 138.6. i've run one down to 137. something (cant remember what it was exactly) there is a risk of valve seats falling out at under 138.6. you pay ya money you take ya chance