Put the dial indicator over the center of the piston as far inboard as you can before you fall off the quench pad and measure it.
All that average rock and crap will just add to the confusion.
Zero the indicator, roll the crank over twice (so you get two readings) and that’s what it IS. Then correct it from there.
You will drive yourself bat crap crazy doing all the averaging and all that. If you get your piston to head clearance to .050 you won’t find a single HP getting it closer. So let’s do some math, assuming you have open chamber heads.
Let’s just guess and say your heads came from the factory on the low side, meaning that the castings needed more materiel machined off to get them flat and clean (relatively), and your heads came through with the recess only .080 deep. Most I’ve measured are .100, but you got lucky. BTW, you have to measure that recess and make the both the same to start with. Can’t just assume they are the same.
Ok, to get your chamber volume where you want it, you deck another .020 off, and the recess is now .060 deep. Throw a typical rebuilders head gasket on there and that recess is effectively .108-.110 deep!
If your piston is out of the hole .020, you have .088-.090 clearance. And yet, if you have everything else right, they won’t rattle at 10.5:1 on cheap pump gas.
That also means if you want to use that thick gasket, you’d need the piston out of the block .050 just to get your .040 quench clearance. And that’s IF it doesn’t raise the CR too high.
Obviously you can use a thinner gasket and not get the piston so far out of the hole.
At any rate, you have to find a machinist who gets tha it’s the RIGHT away to build an engine like this. By this I mean getting the piston out of the hole.
Most guys THINK they have 10.5:1 with those pistons but they aren’t close.
