From http://craig.backfire.ca/pages/autos/boxchevy/350/piston-to-valve-clearance
Piston to Valve Clearance
An important measurement to take when building a custom engine is the piston to valve clearance. There are a few ways to measure it; I chose a simple and accurate method using modelling clay.
The idea is to put a piece of modelling clay into the cylinder, turn the engine a few times, and measure the thickness of the clay. In order for this to work, the valvetrain must be setup completely, or else it is not an accurate simulation of piston and valve location when the engine is actually running. To make things easier, we used light valve springs. The head gasket should also be fitted.
Modelling clay is put into the cylinder to determine piston to valve clearance.
When we first tried to put clay in the cylinder, we had trouble with the clay catching on the valves and stretching out, giving very inaccurate readings. Phil then got the idea to lightly oil the piston face, and wrap the clay in plastic wrap.
Once the clay sample was made by turning the engine twice (it is critical to turn the engine twice, not once), we put the clay into a freezer to help keep it hard, and then cut it in half with a sharp knife. The thinnest part of the clay was then measured to determine the piston to valve clearance. The rule for small blocks is 0.080" for the intake, and 0.100" for the exhaust. In this case, there was plenty of clearance.
The sample was put into the freezer to harden it up, which makes it easier to cut.
The sample is then measured for thickness in the direction of the piston and valve's motion. The thin area to the left is the quench area, which was calculated earlier on in the build process.
Previous: Valvetrain Setup
|
Next: Intake Manifold Gaskets
|
