Piston-Valve Clearance Question

[cj8990]

Need a quick clarification. Piston valve clearance, when measured from the top with a dial gauge, does not actually measure the clearance between the valve and piston but the amount of travel the valve has along the axis of the valve stem before hitting the piston.

When measuring with the clay method however you measure the vertical distance, which would be the distance from the closest point on the radial edge of the valve to the surface of the piston.

Maybe I have something wrong here but when people talk about piston valve clearance which one is the actual correct specification, since these would definitely be different measurements due to the angle the valve stem makes with the top of the piston?

This also makes me wonder.. why do people go through all the trouble of laying clay, assembling the whole engine, disassembly, then measure clay? Couldn't you just use a measured angle the valve stem makes with the deck of the block, valve radius, and the valve travel at TDC you get with the dial method to calculate the same dimension the clay method achieves?

-Corey

 

[miliman13]

Your first sentence. They are the same.
Why the clay method? It only measures the smallest clearance , which is what some people want.

The dial measures at individual degrees.
Your looking to much into it. Your drawing lines were there are non.

Reference jafros videos of you need further clarity.

 

[cj8990]

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So if the valve sits at the green line at TDC then Jafro is measuring the red line with the dial gauge... he calls this the piston-valve clearance. Clay method will measure blue line.. this is not piston-valve clearance, but the actual smallest clearance the valve sees, right? So when people say exhaust valve clearance should be ~.100" that applies to the red line.. not the blue?

 

[miliman13]

Red line= down ward travel of valve

Blue line= upward travel of piston

You measure (piston to valve clearance )
regardless of method.
The numbers from red to blue will be almost identical.
Your looking for .080 to .100 of an inch of travel or space or gap or.............

Using trigonometric functions you could measure distance then calculate angels to solve for this picture. But for what and why?
The purpose is to have more than the minimum specification.

Again your overcomplicating it.