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Interesting find while measuring pushrod length.

Old 03-02-2021, 11:20 PM
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Default Interesting find while measuring pushrod length.

I got around to measuring for pushrods tonight and came across something interesting.

Following the mid-lift method, I set my rocker at 90 degrees to the valves, then turned in 6.5 turns to set geometry. I set-up my pushrods and then tested at mid-lift and rocker arm was parallel to the retainer. Measured 8.025 intake and 8.850 exhaust. These figures include an extra .025 added for preload.

Here’s the interesting part. My dial indicator was showing lift of about .020 greater than what should be there with a 1.7 rocker arm. Lobes are .380 and with the 1.7 rocker I was measuring 667. Any thoughts on why? In another test, I used my Manley pushrod length checker that indicated about a .040 difference in pushrod length (tool requires a shorter pushrod). Adjusting to work with the tool’s findings, left decreased about .035.

The block was decked about .010 and the heads (AFR) have had .030 removed. Lifter are Crane .300 tall dog-bone rollers (roller wheel to the pushrod cup are the same distance as stock, on the upper body is longer).

*edit * Using a dry erase marker, the exhaust sweep pattern was dead center and very thin. The intake was ever so slightly toward the exhaust side, but the sweep pattern was also thin. Not as thin as the exhaust pattern but close enough. Maybe remove .025 to make perfect?

Any thoughts on what’s up here?

Last edited by TomZ; 03-02-2021 at 11:23 PM.
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Old 03-03-2021, 06:04 AM
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I went through the same thing. The only thing I came up with is if you don't get the dial indicator right in line with the valve stem you will get a false reading. AFR heads have a 2* angle on them. Did you use a solid lifter with light checking spring ? You may also need adjustable guide plates. Make sure your roller tip is centered on the valve tip.
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Old 03-03-2021, 09:13 AM
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Hi Tom, I was wondering same thing is if you cked with solid roller. Also did you ck all of them? I often wonder about the people who never even bother checking. In comparison my last builds came in at 7850/8800. Mark lV blocks, dart 310 heads, crane 1.7 rockers. Heads and blocks just surfaced. Regardless something not quite right and should be .646. Keep us posted.

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Old 03-03-2021, 09:40 AM
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Originally Posted by fbc25el View Post
I went through the same thing. The only thing I came up with is if you don't get the dial indicator right in line with the valve stem you will get a false reading. AFR heads have a 2* angle on them. Did you use a solid lifter with light checking spring ? You may also need adjustable guide plates. Make sure your roller tip is centered on the valve tip.
I'm pretty sure I was lined up pretty well with the retainer. I did not use a solid lifter, but I did use checking springs. My lifters have no give right now and with the checking springs, there is no give at all. I can make a solid lifter from a spare OEM lifter (I think I mentioned that lobe contact to pushrod cup measured the same), but with the light checking springs it's probably not necessary.

I was hoping that my plastic pushrod checker would help me verify my mid-lift results. Not the case. I think it is within .050 of accurate meaning just a tad short. A little short is better than little long. Anyway, I was surprised by the measured lift results. I'll check it again when I take a break around noon.

This came up while watching some videos on the subject... Ralph Johnson (if not known, he was one of the contributors to the birth of the SBC) was explaining how to alter geometry and ratio with only pushrod length. He wasn't worried about side-loading the guides. Calculating my results based on some of what he was explaining, I came up with a ratio of 1.75:1. Here's the video if anyone wants to watch it.


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Old 03-03-2021, 10:30 AM
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That is some coincidence of the 1.75 ratio puts you right at or very close to your dial indicator reading...
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Old 03-03-2021, 11:13 AM
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I have found that adj. pushrod checker works well. At .323 of valve lift you can lay a peace of key stock on the retainer and have a line from center to center on the rocker arm. Adjust the pushrod till you get that. I think you will be very close to what your lift should be.
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Old 03-03-2021, 11:27 AM
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I followed that to a tee, that's why I was so surprised. I've got a piece of aluminum bar stock that works perfectly as a sight and I used a straight edge to mark the line through the rocker. I'm using Comp adjustable pushrods. I basically followed Scott Foxwell's walkthru. I must be messing something up because I haven't run into this with my last builds though this is my first set of AFR heads.
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Old 03-03-2021, 12:09 PM
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Make sure your guide plates are keeping the pushrod and the rocker centered ( in line ) with the valve tip.
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Old 03-03-2021, 12:35 PM
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Tom,

Did you actually measure the lobe lift ?
Possible that the rockers are not actually 1.7's ?
I have found that the Manley tool is pretty much worthless on anything other than a stock GM head with stock length valves.

Just thinking out loud

Last edited by BillK; 03-03-2021 at 12:41 PM.
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Old 03-03-2021, 03:15 PM
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Yep, I measured when I degreed the cam. Lobe lift was pretty much on the money. I'm using Crower stainless rockers. I guess I can switch it out to see if the rocker is the issue. I wouldn't think so but can't assume.

Originally Posted by BillK View Post
Tom,

Did you actually measure the lobe lift ?
Possible that the rockers are not actually 1.7's ?
I have found that the Manley tool is pretty much worthless on anything other than a stock GM head with stock length valves.

Just thinking out loud
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