Join Date: Dec 2012
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Milling the head does not effect compression, decking the block does.
Check to see how much the valves are recessed in the head.
Cummins min valve depth spec is .039, max is .060.
If they did a valve job it would have lowered the valves some.
I would have the valves reworked before going to a thicker gasket lowering compression.
Thicker head gasket's are 3 times the price of standard
My block was decked .010, .010 thicker head gasket was over $150, stock is under $50
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