[rod]

Friday I used a friends parts to check valve lift. my goal was to check valve lift with totally different parts. I checked lobe lift and then checked lift at the valve. there was a 020" loss between lobe lift x rocker lift and measured lift. I wondered if it was the way the retainers were machined that the indicator tip was moving. I found two retainers which were both flat [90 degrees to the stem], a small 1.25 and a large 1.437.
with the lifter on the base circle, the pushrod is the same height as the valve tip. using the magic marker on the tip trick, the rocker stays right in the middle of the valve tip.

I measured each situation 3 times to make sure the readings would repeat. all readings were at 0 lash, .100 long pushrod. spring is 120 on seat and 300 open.
lobe lift .363"
using a lite spring;
Crane 1.53 ratio .555"
Crane 1.625 ratio .590
Comp 1.619 ratio .588 [ .363 x 1.62= .588]
[as a note, switching to a factory length pushrod, using the Comp rocker = .583 lift]
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using inner spring only and a larger dia. retainer;
Comp 1.62 .582" [loss of .006"]
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using complete 3 piece spring and large dia. retainer
Comp 1.62 .570" [loss of .018"]

I measured pushrod flex and get .001, which could account for.0025" loss at the valve tip, and less than .001" stud flex [dont know what that does, lift wise].

I got lift loss on a completely different engine, so it is not my parts. I am at a loss for explanation. does every cam do this or.....?

your thought?
Thanks Rod in AZ