measuring lift at the valve

Posted By: Crizila

measuring lift at the valve - 08/27/14 10:04 PM

Decided to take some lift measurements at the valve ( see pic ). On the average, I am coming up about .040" short per valve as compared with the cam specs lift. Is this normal for a 59* stock small block? Solid lifter cam that visually looks good, as do the lifters. Couple of years running on the cam. All the valve train is in good shape. Running very light spring loads ( 110 - 315 ) so I don't see deflection as an issue. All measurements on all valves are within .010", so I don't have one way out of wack. . I accounted for valve clearance. Thoughts?

Attached picture 8253247-valveliftmeasure.jpg

Posted By: dogdays

Re: measuring lift at the valve - 08/27/14 10:17 PM

What you are measuring is correct. The problem is that the lifter is not pushing straight on the pushrod. This was first brought to my attention a few years ago when Rob McC was designing LA rockers for Erson, and was wondering if he should make the true ratio of their 1.6 rockers something like 1.65, in order to get the valve to open exactly 1.6 times the lobe lift. He posted the question in a Moparts forum. I remember trying to figure out why that would be and finally came up with the idea that the actual lift at the top end of the pushrod is the lobe lift times the cosine of the angle between the lifter axis and the pushrod.

R.

Posted By: MR_P_BODY

Re: measuring lift at the valve - 08/27/14 10:25 PM

Pretty normal... are you sure your rocker ratio is
correct.. I get a little less than .040

Posted By: BIG DRAG

Re: measuring lift at the valve - 08/27/14 10:31 PM

That is the way it is for a 59* small block.

Posted By: 70AARcuda

Re: measuring lift at the valve - 08/27/14 11:00 PM

Quote:

What you are measuring is correct. The problem is that the lifter is not pushing straight on the pushrod. This was first brought to my attention a few years ago when Rob McC was designing LA rockers for Erson, and was wondering if he should make the true ratio of their 1.6 rockers something like 1.65, in order to get the valve to open exactly 1.6 times the lobe lift. He posted the question in a Moparts forum. I remember trying to figure out why that would be and finally came up with the idea that the actual lift at the top end of the pushrod is the lobe lift times the cosine of the angle between the lifter axis and the pushrod.

R.

basically cosign of 11 degrees times the gross lift...minus the lash...

then you have the true rocker ratio...which is ???

Posted By: Crizila

Re: measuring lift at the valve - 08/28/14 03:51 AM

Quote:

Quote:

What you are measuring is correct. The problem is that the lifter is not pushing straight on the pushrod. This was first brought to my attention a few years ago when Rob McC was designing LA rockers for Erson, and was wondering if he should make the true ratio of their 1.6 rockers something like 1.65, in order to get the valve to open exactly 1.6 times the lobe lift. He posted the question in a Moparts forum. I remember trying to figure out why that would be and finally came up with the idea that the actual lift at the top end of the pushrod is the lobe lift times the cosine of the angle between the lifter axis and the pushrod.

R.

basically cosign of 11 degrees times the gross lift...minus the lash...

then you have the true rocker ratio...which is ???

- 1.59. Actual rocker ratio = 1.6. Lost .007" lobe lift through the 11* angle.

Posted By: onig

Re: measuring lift at the valve - 08/28/14 04:07 AM

Quote:

Pretty normal... are you sure your rocker ratio is
correct.. I get a little less than .040

Agreed with above statement.
If rocker geometry is off it will affect lift numbers, as well if your pushrod lengths are not correct.

Posted By: Cab_Burge

Re: measuring lift at the valve - 08/28/14 04:47 AM

Have you checked all the rockers at the valves yet? If not do that and let us know what you find for the variences on yours

I've seen .030 difference at the valves on the same brand of rockers, the losss of lift followed the rocker when I swapped them around

I have checked a bunch of stock type Ductile iron Hemi, wedges and LA rockers, Harland Sharps, Crane iron and extruded aluminum roller tip rockers, T&D single shafts and so on

I've yet to see a perfect set that all the rockers lifted the same at the valves

I do have a new set of Jesel paired shaft rockers that I haven't checked or tried to use yet

I'm hoping that they are as good as all the high buck racers say they are

Posted By: Crizila

Re: measuring lift at the valve - 08/28/14 05:37 PM

Quote:

Have you checked all the rockers at the valves yet? If not do that and let us know what you find for the variences on yours I've seen .030 difference at the valves on the same brand of rockers, the losss of lift followed the rocker when I swapped them around I have checked a bunch of stock type Ductile iron Hemi, wedges and LA rockers, Harland Sharps, Crane iron and extruded aluminum roller tip rockers, T&D single shafts and so on I've yet to see a perfect set that all the rockers lifted the same at the valves I do have a new set of Jesel paired shaft rockers that I haven't checked or tried to use yet I'm hoping that they are as good as all the high buck racers say they are

Haven't checked the rockers yet, but I have less than .011" difference from lift readings on all 16 valves, and that is including any cam wear, etc, so they can't be too far off from one another. I'll check a few. Not even sure who's rockers they are as I bought them from Hughes as a package deal. RR350A 1.6 stamped on the tops.

Posted By: mopar dave

Re: measuring lift at the valve - 08/28/14 05:45 PM

I loose about .025-.030" using t&d 1.6 rockers.

Posted By: mr_340

Re: measuring lift at the valve - 08/29/14 06:17 PM

I ended up with ~.475" lift with the .528" MP cam using 273 rockers. The .028"/.032" lash accounted for most of the loss, the rest probably in the 273 rocker ratio being less than 1.5.

Posted By: moper

Re: measuring lift at the valve - 08/29/14 06:28 PM

... and it's worse with hydraulic roller lifters - shorter pushrod = more angle. It's fairly subjective but in my experience it's .018-.022" less with 1.5s in most circumstances.