Checking P/V clearance discussion
I posted a similar question back in 2006, using the clay method:
https://ls1tech.com/forums/showthrea...84#post4189484
and I get different results.
multiplying the green values (your 'Y' values) times .966 (AFR head on mine too) I should get the amounts that are reflected by the blue arrows (your X).
https://ls1tech.com/forums/showthrea...84#post4189484
and I get different results.
multiplying the green values (your 'Y' values) times .966 (AFR head on mine too) I should get the amounts that are reflected by the blue arrows (your X).
Last edited by ROCNDAV; Jul 22, 2008 at 06:32 PM.
Actually the blue arrows in your picture are showing the radial clearance from the edge of the valve to the edge of the relief. That distance won't change with lift. It is set by valve diameter and the location of the guide.
I edited your pic with the new arrows showing the distance you would measure with a dial indicator on the valve:
I edited your pic with the new arrows showing the distance you would measure with a dial indicator on the valve:
For example, if you have 15 degree valve angles and get .100" p/v on a valve with the dial indicator, you actually have .096" TRUE p/v clearance
When you are getting pretty close on clearance, that could the difference in leaving the cam or moving it.
So people don't get confused, this is only used with dial indicators. The clay is showing actual numbers assuming you don't smash or distort the clay at all.
When you are getting pretty close on clearance, that could the difference in leaving the cam or moving it.
So people don't get confused, this is only used with dial indicators. The clay is showing actual numbers assuming you don't smash or distort the clay at all.
I see what ur sayin Frito, but the difference you're talking about is miniscule. You are correct that if you press the valve in, because of the valve angle the x and y axis do not change exactly the same. If the .004 difference in PTVC is a concern though, you really ought to rethink your setup.
For the record....I use a dial indicator but have no qualms with using clay if the situation were to arise.
For the record....I use a dial indicator but have no qualms with using clay if the situation were to arise.
I was going to comment but was already beaten to the punch.
With a 15 degree vavle angle, the difference in distance (in thousandths of an inch) between doing the clay method and doing the valve spring drop method is pretty tough to measure accurately. We're talking in the magnitude of individual thousandths of an inch, which if that makes or breaks your engine, flycut some more or go with a smaller cam.
With a 15 degree vavle angle, the difference in distance (in thousandths of an inch) between doing the clay method and doing the valve spring drop method is pretty tough to measure accurately. We're talking in the magnitude of individual thousandths of an inch, which if that makes or breaks your engine, flycut some more or go with a smaller cam.
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I learned the dial indicator method. Everyone I know measures that way, and no one's ever had an issue...Including motors running the bare minimum ptv.
You're splitting hairs. Both methods work, the dial indicator with light springs is much more precise.
You're splitting hairs. Both methods work, the dial indicator with light springs is much more precise.
I see that now fellas. Mr jammin' pulled out the cosine stuff for us which was a big help. I didn't have many jumping in here saying that they knew all about it when Brad was in denial with me 
It is only 4 thousandths difference at one hundred thousandths clearance. It is easy to see what the difference is now. So about 2 thousandths difference at fifty thousandths clearance and so on..... BUT there is a difference and that is what I was wanting to point out.
It is only 4 thousandths difference at one hundred thousandths clearance. It is easy to see what the difference is now. So about 2 thousandths difference at fifty thousandths clearance and so on..... BUT there is a difference and that is what I was wanting to point out. 
I actually did increments of 5* from 20*-5* before and after TDC, just out of curiousity.