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90* Midlift on Pivot Ball Rockers

General engine tech -- Drag Racing to Circle Track

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RevTheory
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90* Midlift on Pivot Ball Rockers

Post by RevTheory » Tue Oct 29, 2019 1:18 pm

A forum buddy of mine is setting up his rocker geometry and we were hoping to use Scott Foxwell's video but we've run into a snag in getting the line drawn through the body of the rocker.

We were thinking with some fancy footwork and measuring, we'd be able to locate where the body actually pivots being that there isn't a trunion to draw your center from but now I don't think that's possible.

Do you guys know if it's possible to use Scott's method on a pivot-ball rocker?


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Re: 90* Midlift on Pivot Ball Rockers

Post by cjperformance » Tue Oct 29, 2019 4:17 pm

A rough trick to find the ball pivot center is to fit a rocker and ball onto a stud, looking side on at the rocker draw a line down the the rocker body thats parallel to the stud centerline. Now pivot the rocker back and forth and pick the point on the drawn line that stays at the stud centerline. This is your approx pivot center. You will be very close and need just tweeking of pushrod length to then get your sweep pattern nice.
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RevTheory
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Re: 90* Midlift on Pivot Ball Rockers

Post by RevTheory » Tue Oct 29, 2019 4:21 pm

Thanks, Craig. We'll give that a go.

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Re: 90* Midlift on Pivot Ball Rockers

Post by SchmidtMotorWorks » Tue Oct 29, 2019 9:14 pm

You can do it precisely.

Use an adjuster with a set screw.
After you set clearance remove the rocker and put the ball and adjuster back at the level it was.II
Measure from the valve tip to the top of the ball.

Remove the ball and figure out the distance from the center if the ball to the top.

Layout the dimensions on paper or even better in CAD.

You can easily do this within 0.005".

No read to involve the rocker body other than the first assembly to find the level for the nut.
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Re: 90* Midlift on Pivot Ball Rockers

Post by Walter R. Malik » Wed Oct 30, 2019 9:29 am

RevTheory wrote:
Tue Oct 29, 2019 1:18 pm
A forum buddy of mine is setting up his rocker geometry and we were hoping to use Scott Foxwell's video but we've run into a snag in getting the line drawn through the body of the rocker.

We were thinking with some fancy footwork and measuring, we'd be able to locate where the body actually pivots being that there isn't a trunion to draw your center from but now I don't think that's possible.

Do you guys know if it's possible to use Scott's method on a pivot-ball rocker?

As long as it has a roller tip.
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MadBill
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Re: 90* Midlift on Pivot Ball Rockers

Post by MadBill » Thu Oct 31, 2019 5:48 pm

Couldn't you just use or make a radius gauge for the ball and then calculate the centerline dimension up from the the contact surface of the arm?
(And if the rocker doesn't have a roller tip, the line goes through the valve contact point of the pallet.)
Felix, qui potuit rerum cognscere causas.

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Re: 90* Midlift on Pivot Ball Rockers

Post by cardo0 » Thu Oct 31, 2019 9:32 pm

If your using piviot ball rockers your using less than 1/2" lift at the valve (or your should be using full roller rockers over 1/2" lift). Why make it so difficult? Just use a Moroso or Proform p-rod checking tool? Like only 10 bucks. Close is good enough even more so using the flat tipped stamped rockers. Just look at the p-rods vendors sell in only what 0.020" increments (unless you spend for custom p-rods) - close is good enough. A plastic checking tool and set of feeler gauges is all you need. 10 minutes and done. You can always verify the contact patch. If you actually had over say 0.550" lift at the valve you might see a difference but as mentioned previously you shouldn't be there using piviot ball rocker arms.

You think you will make any more power using that video? You will soon find that video fails to show you how to measure 1/2 of Max lift. For the novice enthusiest that's leading him over a cliff. To measure 1/2 Max lift you need either a specialty tool or convert a solid lifter to one.

Have fun is all I can say now.

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Re: 90* Midlift on Pivot Ball Rockers

Post by RevTheory » Fri Nov 01, 2019 8:51 am

Yeah, he's got a solid lifter and an adjustable pushrod. We just didn't anticipate finding the fulcrum center being quite as tricky as it was.

Craig's vertical line trick may have paid off. We'll know more after he gets back to it over the weekend. If something still doesn't seem right, we'll just do the wear line across the valve trick and call it a day.

I appreciate the input.
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Re: 90* Midlift on Pivot Ball Rockers

Post by MadBill » Tue Nov 05, 2019 12:49 am

In theory (and my practice) "90 °Mid-Lift" and "minimum sweep" result in exactly the same pushrod length, but sweep is easier to measure as accurately as your dial indicator will read.
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