"How Too" measure piston head clearance accurately ....

This info is for engines with CAST IN HEADS

Many folks just use soft solder threw the spark plug hole Unfortunately this cocks the piston in bore and loads up the bearings giving a FALSE measurement.

In a HIGH performance motor you need to set it up by knowing the actual Mechanical clearance with piston nice and square within bore.

To find "Actual" clearance you must remove cylinder & piston. (Remove ring from piston.)

Using a depth Micrometer or "** Dial Calipers **
Insert piston into cylinder and put it up into head
until it stops at TDC , Hold it there & measure threw plug
hole the distance from center of piston (High spot) to
edge on spark plug hole ... Write down this distance.
Next put piston back onto rod w/o ring or a base
gasket ***
Lightly tighten cylinder back onto cases.
Next move piston up to TDC & remeasure distance from
plug hole to top of piston. Write this distance down.

*** Now subtract the two #'s from each other. The # you are left with is the "ACTUAL" mechanical clearance
within the engine.

You adjust as needed by adding/decreasing gasket thickness or machining
the base of cylinder.