[Geoff]

HWY,

So why is it 'wrong' If the roller is more to the 'outside'? Or more to the 'inside'?
What does it change? The actual ratio is changing during the cycle of opening & the valve. Smokey Yunick explains this well in his book.
In the usual attempt to get a narrow centered pattern on the valve tip, you need to change prod length. So what will THAT do?

The now defunct PE magazine did a test on different length prods with different rockers, testing how TOTAL valve lift was affected. Three prod lengths were tried & three rockers: 1.5 & 1.65 stamped & 1.65 roller tip
Advertised lift was 0.587". The measured lift varied from 0.521" to 0.592". The longer prod gave the highest lift. So working to get a centered pattern on the valve tip might require a shorter prod...& give less lift.
Crane brought out quick-lift rockers that had faster off the seat lift & they did this by lowering the prod seat.
Rocker geometry is complex & there is no right or wrong way.

[steve25]

In general there’s no doubt that the more spring pressure you need to run then getting the pattern as centered as you can needs to also be considered with how long will the motor need to run with a less then a optimal pattern.

In a drag motor faster valve guide ware can be tolerated more then a endurance motor which to me includes a street motor that the owner wants to have live for 30k plus miles.

[HWYSTR455]

Originally Posted by Geoff

HWY,

So why is it 'wrong' If the roller is more to the 'outside'? Or more to the 'inside'?
What does it change? The actual ratio is changing during the cycle of opening & the valve. Smokey Yunick explains this well in his book.
In the usual attempt to get a narrow centered pattern on the valve tip, you need to change prod length. So what will THAT do?

The now defunct PE magazine did a test on different length prods with different rockers, testing how TOTAL valve lift was affected. Three prod lengths were tried & three rockers: 1.5 & 1.65 stamped & 1.65 roller tip
Advertised lift was 0.587". The measured lift varied from 0.521" to 0.592". The longer prod gave the highest lift. So working to get a centered pattern on the valve tip might require a shorter prod...& give less lift.
Crane brought out quick-lift rockers that had faster off the seat lift & they did this by lowering the prod seat.
Rocker geometry is complex & there is no right or wrong way.

I agree with much of what you said, but disagree that there 'is no right or wrong'. You can't just throw any length pushrod on there and expect it to work properly, or there would be no reason to check it.

Rocker ratios for most arms are all over the board, especially on the cheap ones. Centering the pattern may do exactly what you describe, it may require a shorter pushrod, but not give max lift. That's one reason why you calc it at half lift. The pattern may be to one side or the other, but the geometry would be correct.

In the example you provided for testing, the longest pushrod was probably the one closest to the 'correct' geometry.


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[HWYSTR455]

Originally Posted by steve25

In general there’s no doubt that the more spring pressure you need to run then getting the pattern as centered as you can needs to also be considered with how long will the motor need to run with a less then a optimal pattern.

In a drag motor faster valve guide ware can be tolerated more then a endurance motor which to me includes a street motor that the owner wants to have live for 30k plus miles.

True. Side loads matter at higher spring psi, and using the half lift method usually does center the pattern.

Pushrods also have more deflection as spring psi's rise.

The more lobe lift there is, the more likely the pattern width is wider.

Depending on the lobe design, the half lift point may be lower or higher on the ramp. But it will never be abstract.



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[MPKind]

I have to comment on this. Last year I got all swept up in this mid-lift geometry stuff by some guy...I forget his name. Sounded really good on paper, and from a mechanical/physics standpoint, it made sense. So we attempted to dial in the pushrod length by that method. Total fail. The valve tip pattern was offset similar to your pictures or worse. So we went back to the "witness mark centered on the valve tip". We used a large caliper and experimented at 0.050" even increments since that's how most (not custom) push rods are mass produced. Once we found the one that made the best pattern, that was it.

I'm using the short style pre-67 valve covers with Crower Enduro SS roller rockers with the shorty "Sure Locks". Also using the thickened 1/4" valve cover gasket from BOP Engineering or Tin Indian....I forget. I have clearance.

The reason why the mid-lift does not work as advertised is because the rockers we buy are not designed specifically with mid-lift geometry in mind. They work great out of the box using the witness mark method.

[chuckies76ta]

Originally Posted by 1975ta

The lifter is pumped up and has some springiness to it. I checked the pushrod length using the geometry method and came up with 5.21 turns on the polylock and got a length of 9.1 in for my pushrods.

Isn't the lifter suppose to be as solid as possible for push-rod measurement? Are you checking pushrod length with the double springs installed or a valve checking spring?

Another thing that was mentioned was the stud length. You want to make sure you have good thread depth into the poly-locks. I believe a bit longer rocker stud is not gonna cause your poly-locks to sit higher. you will just end up with the same height poly-lock, but have more thread engagement on the poly-lock.

I have replaced them when the studs are too short. ARP makes different lengths. A friend of mine broke a poly lock because studs were to short.

Also mentioned, make sure those rocker bodies are not touching the retainers at any point in the lift.

I also don't like your pattern on valve stem as it could be centered better.
From what I understand, inboard is better than outboard as it puts less wear on the valve stem. Centered and narrow is your friend.

I also like this guys video.
https://www.youtube.com/watch?v=o5is9BsH5OU

[1975ta]

I used a valve checking spring during the half lift test. I thought the lifters should be lashed a 3/4 turn like usual when testing. But still the geometry is not to be desired. I will contact butler today and order another set of rockers to try and find a better design. I’m looking at the Pontiac specific designs they have. I will probably return the comps as I want the geometry to be perfect for the amount of money I am spending on this motor. The rocker never touches the retainer. I hope seperate prod lengths are not required as it’s a pretty basic cam and motor setup. I have the butler #8022 cam. I think I will try different rockers first before longer studs because then I would run into issues with the valve covers again due to a longer prod of 9.5 in measured by the contact area in the center of the valve stem. That may be the final solution but it seems pretty long for a Pontiac and the wear pattern was larger than the 9.1in.

[chuckies76ta]

Good that you used a checking spring.

Not meaning to tell you what to do, but seeing you have spent a bunch of money anyway. Get yourself a set of 1.5 Crower Stainless rockers. Yes the studs might be ok with different rockers. Another nice set of rockers is the Harland sharpe. I have run the Crower rockers for years with no issues.

[chuckies76ta]

What lifters have you gone with?

[1975ta]

I have the comp cams evo hyd roller lifters.

[1975ta]

The crowers are a little pricey, anybody have any experience with the butler stainless pro series rockers? They are on sale right now and look pretty similar to the crowers. If the crowers really are the best I might just have to go with them.

[HWYSTR455]

All I run is the Crowers, (they are the best before going into shaft-mount), except on the Olds/Bernard-head stroker, I use the Bernard moded HS ones. I run the Crowers on a solid roller and one with EOVs, never had an issue with the half lift method.

When you use the half lift method, type of lifter doesn't matter, you don't compress it at all when you're measuring. So you don't need a light spring, at all. The cam is on base circle, and the cam never moves, so the valve never moves.

You don't calc the lash into the measurement, regardless of HFT, HR, or solid.

I'm not sure how a Crower rocker wouldn't be designed for using the half lift method, the rocker doesn't change anything in relation to the trunnion and the roller tip.

The rocker tip travels in a slight arch, and if you have the geometry set at half lift, the pattern will be as narrow as physically possible. It might be a hair towards the stud, but with deflection, it cancels that out.

If you try to get the pattern more away from the stud by using the pattern, the pattern will be wider.


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[1975ta]

Whenever I did get the pattern centered on the valve stem, it was much wider, so I think I will probably send back the comp rockers and get the crowers.

[HWYSTR455]

Originally Posted by 1975ta

The crowers are a little pricey, anybody have any experience with the butler stainless pro series rockers? They are on sale right now and look pretty similar to the crowers. If the crowers really are the best I might just have to go with them.

Those Butler rockers are re-branded PRWs:

https://www.summitracing.com/parts/p...1/make/pontiac


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[HWYSTR455]

Originally Posted by chuckies76ta

Isn't the lifter suppose to be as solid as possible for push-rod measurement? Are you checking pushrod length with the double springs installed or a valve checking spring? ...

I also like this guys video.

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

That's my-go to vid for half-lift method references, posted that link in post #10.

If you look at that vid, he never turns the crank/cam, so it doesn't matter if you have a checker spring on there or not.


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[Lee]

Two things to add here:

1. I used a set of CompCams Pontiac rockers a few years ago. The pushrod length required to get the geometry I wanted, was longer than expected. I have a set of Crower rockers sitting around, which have test-fit about the same as Harland Sharp and PRW rockers on various motors - so I tested them against the Comp rockers. The Comp rockers required a pushrod 0.300" longer than the Crower.

2. I recently built a motor with a set of (owner supplied) PRW aluminum rockers. Using the "half lift" method as well as my version of the "centered on the stem" measuring, I got the same pushrod length. Speedmaster heads, PRW "1.65" aluminum rockers.

EDIT: NO IDEA why the photo is sideways on here, it is not that way on my computer.

[steve25]

I know this is not the race section so this info might not matter much to some, but here is why patterns produced by the same ratio rockers can be different with the same length push rods being used.

These charts were made by David Vizard using BBC rockers.

Note in particular how the initial ratio can be by very different even though the advertised rocker ratio is the same!

This is also why some motors running the same ratio rockers can be down or up by 8 to 10 hp.

[grivera]

Originally Posted by HWYSTR455

That's my-go to vid for half-lift method references, posted that link in post #10.

If you look at that vid, he never turns the crank/cam, so it doesn't matter if you have a checker spring on there or not.


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It needs a light spring cause he’s opening the valve to half lift and checking for 90 degrees at that point. He used a light spring in the video.

[steve25]

Here ya go.

[Lee]

One thing about the "half lift" instructions going around, that bothers me - where to draw the line.

Everyone is drawing the line to the center of the tip's fulcrum. A physics teacher taught me to consider absurdities, when "mentally" looking at such things. The center of the tip's fulcrum will vary according to the diameter of the roller - a 1" roller tip (absurdity, I know) would create a crazy looking valvetrain.

The contact point, the tangential point of contact between the valve stem and the roller - that seems like to where the line SHOULD be drawn, to me.