lost valve lift part II
 

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

Re: lost valve lift part II
 

I'm not familiar with your engine or the parts you are testing. I'm going to assume all the rocker arms are aluminum. It would be interesting to check a steel rocker arm and see how it compares. The modulus for steel is 3X higher than aluminum, so it deflects less. The density is also about 3X higher as well. The ideal rocker arm material is beryllium, which has a modulus about 5X higher than aluminum and is lighter than aluminum or magnesium. Too bad there are health issues machining it and of course, it's expensive.

Re: lost valve lift part II
 

In division 5 they drive a razor blade in-between spring and retainer,then measure off the razor blade that is flat. Tom

Re: lost valve lift part II
 

You might want to check it after establishing correct rocker geometry at mid lift....regardless of where the roller tip is relative to the center of the valve stem. Ths video is a good one:

https://www.youtube.com/watch?v=o5is9BsH5OU

Re: lost valve lift part II
 

Good video! Thanks

Re: lost valve lift part II
 

The rest of your lift loss is in cam flex and rocker arm flex. Also, you should check the lift with ALL the pushrods and springs in place (just like it's run).

Re: lost valve lift part II
 

the rockers are Comp stainless. while there could be flex, I cant see .020"
for future ref., I do like the idea of the razor blade-nice and flat.
I have given the idea of cam flex a great deal of thought.
one thing I want to check is how much clearance there is between the journal and the bearing.
I have tried several different lengths of pushrods and even a checking PR. no change.
I can see several thou. stack flex. but I cannot see .020.
I still wonder if others are having this problem and do not realize it. beings that my friends engine showed the same loss.
thanks for the ideas all.
Rod in AZ