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Discussion Starter · #1 ·
Working with some old "Pontiac" #427 bbc heads, Jesel shaft rockers. - These heads are similar to conventional BBC valvetrain, utilizing all centered 1.65" pivot length rockers which is one of their pitfalls being difficult to get geometry happy with bigger lifts(.960 theoretical with my cam and the 1.8 ratio rockers I'm wanting to use).


If I set the stand height to be 90* at mid-lift, my A-B-A travel is a good bit off in doing so. Rocker tip starts on center of stem, sweeps out ~.025, then back under about ~.050(total sweep ~.075). I can move the stands in towards the valve stem and center the sweep more but A-B-A stays off pace accordingly

If I drop the stand height ~.060, I'm noticeably short of 90* at mid-lift, but my A-B-A is better and total sweep across the stem is lower with the tip starting ~.030 behind center, sweeping out ~.030 past center then back to ~.030 behind(total sweep ~.060) - This also puts the "B" point at mid-lift.

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I fully understand I will have to compromise due to the pivot length vs lift, but I'm not sure which is "best"? - I'm thinking the better A-B-A and lower sweep is more logical, but being the rocker mfg's typically call for 90* at mid-lift I was curious what some of y'alls thoughts are on the matter.

Thanks,
- Jp
 

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Discussion Starter · #4 ·
Thanks guys, that is my thinking as well. I was somewhat surprised that setting it 90* at mid-lift didn't put it at "B" of the sweep, but I'm assuming that's just one of the inherent issues of these old heads especially with long valves and this much lift.

I've read many times about these heads having issues at/above 1" lift with no real data/reasoning to correlate the issue; honestly I'm thinking its more likely valvetrain geometry becoming an issue at that point than the port.
 

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The second setting, along with needle bearing tips will be the best option you have, IMHO.
 

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I agree. Just quite cant understand how sweep and 90* can be off.
They can't. It's math and geometry, it's not arbitrary. You're doing something wrong in the process or with your calculations. 90* geometry HAS to give you a symmetrical A-B-A movement, or it's not 90* geometry. It will also give you the least amount of sweep possible.
This is for stud mount rockers but the principles and goals are the same. Maybe it will help;

One thing to also remember; Jesel does not design their rockers around a 90* geometry. If you set the rockers up this way, the pushrod side will be way off and you'll most likely toss pushrods. I would talk to Jesel and get their geometry recommendations for setting up these rockers.
 

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They can't. It's math and geometry, it's not arbitrary. You're doing something wrong in the process or with your calculations. 90* geometry HAS to give you a symmetrical A-B-A movement, or it's not 90* geometry. It will also give you the least amount of sweep possible.
This is for stud mount rockers but the principles and goals are the same. Maybe it will help;

One thing to also remember; Jesel does not design their rockers around a 90* geometry. If you set the rockers up this way, the pushrod side will be way off and you'll most likely toss pushrods. I would talk to Jesel and get their geometry recommendations for setting up these rockers.
T&D does set them up around 90* geometry dont they?
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Discussion Starter · #9 ·
I have only set up a few sets and previously just went by the a-b-a pattern and total sweep. Just noticed while checking that these don't appear to be 90* at mid-lift as I'm used to seeing with T&D's. - Maybe if I played with the backspacing more I would find it, but given the wider sweep with the taller stand height I didn't see the point in further shuffling the stand.


I can't wrap my head around what doesn't seem to look right. I fully agree with Scott and others that the rocker arc is a set travel path and mid-lift is mid arc per shimming and should be able to be set at 90. - Maybe the rocker pad angle isn't properly correlated to the valve/spring pocket angle? Thusly I'm turning the stand some to center the tip after changing the shimming which results in a difference of the visual angle relationship between the rocker and valve?



I'm kinda at the point of "whatever". Sweep & a-b-a are both good at the one shim height/back spacing, probably need to quit over-thinking it.
 

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Not quite on subject, but the last 2 T&D set ups were disappointing. AFR 357 and Dart Pro 1. These heads have been around for years but the rocker stands put the center of the rocker roller .040' toward the exhaust side and the left to right position off too. Sheldon was not very energetic to get to the solution even though I think he was aware the problem exists. He did take the original stands back and made new "custom" stands that corrected the issue, but had to pay $200 on top of the
$1350 original cost. I felt like they should have this fiqured out by now and he felt like it was both the head companies fault for changing thing around, which they did not do.

Once correct, they have been bullet proof.
 

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Not quite on subject, but the last 2 T&D set ups were disappointing. AFR 357 and Dart Pro 1. These heads have been around for years but the rocker stands put the center of the rocker roller .040' toward the exhaust side and the left to right position off too. Sheldon was not very energetic to get to the solution even though I think he was aware the problem exists. He did take the original stands back and made new "custom" stands that corrected the issue, but had to pay $200 on top of the
$1350 original cost. I felt like they should have this fiqured out by now and he felt like it was both the head companies fault for changing thing around, which they did not do.

Once correct, they have been bullet proof.
They should have corrected it for free!!!!
 

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Jesel is so much better, unless maybe you get steel rocker TD
I'd have to see proof of that.
What material is so much better and how is it so much better?
What's the difference in deflection and was it an A to B test?
 
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