lost valve lift?

[rod]

in the process of degreeing in a cam [327 SBC}...I have a checking head with only 2 valves and a lite spring. everything was right, so I moved on the the head which I would be using with the valves and springs which would be used. I lost about .025" lift. I put the checking head back in place and the #s came right back. I changed rockers and nothing changed and changed 3 different length push rod, no change. back the the real head and the lift is gone again. did the same, changed rockers and push rods. even tried different ratio rockers and lift is just gone. the springs are only 120 lbs on the seat and 310 over the nose, so nothing mongo. I put the dial indicator on the side of the push rod to check deflection and only got.001", which could account for .0025" lost lift. then I checked the stud [7/16"] and got .001 towards to valve [which should be a + not a -, right?]. swapped in a brand new stud, no change. next I pulled the cam out and replaced it with a stock 350 hyd. cam [using a solid to check] with the lite spring and a 1.6 rocker, the lift comes out at .414" @ 0 lash, which is what the lobe lift x 1.6 is. I then put the race spring on the checking head and I get .403". so even with a low lift cam I loose .011 lift.
I have a brand new set of stainless 1.6 rockers which check the same as a 1.6 Crane gold, I have 1 Crane 1.52 rocker and 1 Harland Sharp 1.52 and all 4 rockers check out the same [of course the 1.52 have a different lift, but still short of true gross lift] with the lite spring and all test out the same with the race spring, regardless of head used.
I can understand loosing a few thou. from stack up, but not .025 or even .011 on a low lift. so where the heck is my lift? what is it that I am missing or over looking?
any ideas or help will be greatly appreciated.
Thanks Rod in AZ

[Alan Roehrich]

The quickest way to diagnose your problem is to install checking springs on the head you intend to use, shim it up off the block to simulate a head gasket, then check lift with the rockers you intend to use and a checking pushrod.

[Stewart Way]

I am far from an expert on this but I'll throw this out for comment. Your checking head and your race head appear to be different enough to make a difference in the set up angle between the valve centerline and the rocker intersect line. If one head is cut more or angle milled I would think you would see a difference in valve lift. What I don't understand is how you can use 3 different length pushrods and not get some difference in lift.

[FED 387]

has the low lift head deck surface been resurfaced a substantial amount?? try a 3rd head on the block see if maybe you cut that head more than you think you did also try checking all 3 heads on the other bank--- maybe when you decked the block you took off more on one side than the other --- try putting a straightedge on both the head surface and the block deck surface see if for some strange reason they are not flat - do not remember if you said you were checking with a head gasket--- might measure it in several places see if it is the same thickness at several points--look closely see if the rocker arm is hitting the v spring retainer --- I would try one head on both sides of the block see if there is the same variation then swap over 2 lifters then 2 pushrods see what happens---might try measuring EACH cylinder to see if the lift variation is consistent from one cylinder to another

[Jamie Greening]

It's all in the difference in spring pressure. Been there done that on a stocker cam. Always check lift with your spring that you are going to run. I thought I had a cam that was too big once because of checking springs. Had it redone for proper lift then once I installed my normal springs I lost the lift I had ground off.

[CFMCNC]

There will always be a loss at the valve going from a checking spring to a loaded valve train,One example cam card says 1.085 lift but after lash,bend and flex it was 1.013,another came card says 1.040 but NET was .977.This loss should be applied to spring height set up as it will affect coil bind.WE like to see .050-.100 to coil bind.Bill C.

[Mike Taylor 3601]

I would make sure that there is no binding of pushrod against guide plate,head etc where it has pushrod not seated in pushrod seat,like some others said when you have the full pressure of springs can lose lift.
If tip of valve is higher on your head that loses lift,that causes tip of valve and rocker stud to be closer,which puts tip of valve closer towards intake and roller of rocker out towards exhaust which is same as reducing rocker ratio.
Mike Taylor 3601