Rockers too high on the studs?

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PRH
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Re: Rockers too high on the studs?

Post by PRH »

My friend has been running Scorpions on his Stocker since the rule changed...... which iirc was 2012.
No problems at all so far.

I know of several sets that have been put into service locally on BBC marine apps...... no problems with those either.
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Re: Rockers too high on the studs?

Post by midnightbluS10 »

MadBill wrote: Sat Dec 28, 2019 11:32 pm
travis wrote: Sat Dec 28, 2019 10:39 am I’m measuring for pushrod length and something seems off here. It doesn’t seem to matter what length I set my adjustable pushrod measuring tool at...each time the tip pattern is nice and tight even if it isn’t in the center...

58461412-BDB7-40F6-9E40-F9DD9ADE9E8C.jpeg
Looks like you're closing in on a resolution, but a couple of comments:
First, by pure geometry, the sweep cannot remain the same when the pushrod length (and thus the rocker angle) changes, as a simple drawing will show.
Also, unless your gross lift is less than 0.400", the photo shows a too long pushrod, since the rocker-to-retainer "up" angle above the retainer with a closed valve will clearly be much smaller than the "down" angle at full lift, as the Straub/"90° at half lift" approach ensures.
Lastly, not all will agree, but the pushrod length should not be changed to center the roller. If it isn't in danger of overhanging the valve tip leave it be, to maintain minimum sweep. If it's far out, you need a different rocker.
Is that the same as the Jim Miller designed mid-lift method?
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Re: Rockers too high on the studs?

Post by jed »

travis wrote: Mon Dec 30, 2019 3:18 am In the photo, the valves are closed.
If both valves are closed and the Int and ex lifters are on the base circle. The push rod ends of the rockers should be at the same height. They are not.
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Re: Rockers too high on the studs?

Post by n2omike »

Rocker geometry is either right... or it's not.

The rocker should be fairly square to the stud at mid lift. It doesn't need to be EXACTLY square at mid lift, but in the ballpark. Sometimes people will chase absolute minimum sweep, and end up with the pushrod side of the rocker way up in the air, which definitely isn't good.

Minimal sweep is important, but it also has to occur with the rocker being roughly square with the rocker at mid lift. Shoot for no more than 0.080" sweep. The pattern should also be roughly at the center of the valve tip. If it's off just a tad, that's okay.

These are all rules of thumb. Don't completely sacrifice any ONE of them in order to optimize something else. Make sure all three are acceptable.

If you simply cannot get it to work, try some different rocker arms.

Good Luck
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Re: Rockers too high on the studs?

Post by MadBill »

midnightbluS10 wrote: Mon Dec 30, 2019 10:18 am...
Is that the same as the Jim Miller designed mid-lift method?
Essentially, yes. Here's another thread to add to the confusion: viewtopic.php?t=44986
Despite at least one assertions in it, 90° and minimum sweep do coincide re required pushrod length. Tip: the pushrod side of the arm has nothing to do with this concept.

Again, a large scale drawing of the valve side of the arm will clarify things.
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Re: Rockers too high on the studs?

Post by Walter R. Malik »

midnightbluS10 wrote: Mon Dec 30, 2019 10:18 am
MadBill wrote: Sat Dec 28, 2019 11:32 pm
travis wrote: Sat Dec 28, 2019 10:39 am I’m measuring for pushrod length and something seems off here. It doesn’t seem to matter what length I set my adjustable pushrod measuring tool at...each time the tip pattern is nice and tight even if it isn’t in the center...

58461412-BDB7-40F6-9E40-F9DD9ADE9E8C.jpeg
Looks like you're closing in on a resolution, but a couple of comments:
First, by pure geometry, the sweep cannot remain the same when the pushrod length (and thus the rocker angle) changes, as a simple drawing will show.
Also, unless your gross lift is less than 0.400", the photo shows a too long pushrod, since the rocker-to-retainer "up" angle above the retainer with a closed valve will clearly be much smaller than the "down" angle at full lift, as the Straub/"90° at half lift" approach ensures.
Lastly, not all will agree, but the pushrod length should not be changed to center the roller. If it isn't in danger of overhanging the valve tip leave it be, to maintain minimum sweep. If it's far out, you need a different rocker.
Is that the same as the Jim Miller designed mid-lift method?
The problem with that is, rockers which are not designed for that type geometry, sometimes don't work very well when trying to use it with them.
You need to try to use whatever type geometry those particular rocker arms are designed to use.
So many things go into it such as valve spring cut-away, pushrod cup location and angle, stud slot placement ... including designed compromises in order to fit a number of different applications.
So, use the geometry THAT particular design application wants ... finding "that" while testing everything to get the best end result is what needs to be done.

Attempting to use the wrong rocker arm for that application is never a good idea.
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Re: Rockers too high on the studs?

Post by steve cowan »

PRH wrote: Mon Dec 30, 2019 10:16 am My friend has been running Scorpions on his Stocker since the rule changed...... which iirc was 2012.
No problems at all so far.

I know of several sets that have been put into service locally on BBC marine apps...... no problems with those either.
I to have used scorpion 1.6/1.5 rockers in a flat tappet application with no signs of distress, freshening a 383 at the moment and will be using scorpion rockers 1.6/15 on a mild roller to 600" lift and 580 lbs /in spring rate,in a stud mount set up I always use 7/16 studs and a quality stud girdle even on SFT.
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Re: Rockers too high on the studs?

Post by travis »

jed wrote: Mon Dec 30, 2019 10:28 am
travis wrote: Mon Dec 30, 2019 3:18 am In the photo, the valves are closed.
If both valves are closed and the Int and ex lifters are on the base circle. The push rod ends of the rockers should be at the same height. They are not.
I only had a pushrod length tester on the intake side in that picture
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Re: Rockers too high on the studs?

Post by gmrocket »

travis wrote: Mon Dec 30, 2019 4:29 pm
jed wrote: Mon Dec 30, 2019 10:28 am
travis wrote: Mon Dec 30, 2019 3:18 am In the photo, the valves are closed.
If both valves are closed and the Int and ex lifters are on the base circle. The push rod ends of the rockers should be at the same height. They are not.
I only had a pushrod length tester on the intake side in that picture
You went from 8" down to 7.7" and you say it still looks to high? Hard to picture that considering how it looks with the 8" rod

Can you post a pic with the 7.7" in there?
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Re: Rockers too high on the studs?

Post by travis »

What I meant by "looking too high" is that the rocker, even with the "proper" length PR for this setup, is still sitting too far up on the stud.

I've already got the head off and everything masked for paint, so no more pics at the moment.

Out of curiosity, I drug my last remaining sbc out from under the bench, stuck a 305 head on the short block, and mocked everything up with these rockers. Everything looks perfect with a stock length sbc pushrod. So, it appears to me that everyone who said this was an sbc rocker, was correct.
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Re: Rockers too high on the studs?

Post by gmrocket »

travis wrote: Mon Dec 30, 2019 11:04 pm What I meant by "looking too high" is that the rocker, even with the "proper" length PR for this setup, is still sitting too far up on the stud.

I've already got the head off and everything masked for paint, so no more pics at the moment.

Out of curiosity, I drug my last remaining sbc out from under the bench, stuck a 305 head on the short block, and mocked everything up with these rockers. Everything looks perfect with a stock length sbc pushrod. So, it appears to me that everyone who said this was an sbc rocker, was correct.
Ok, but the pic SMW provided with the lines showing where the pivot point should be at mid lift seems like it would have been just about right on with the 7.7" rod length.. dropping your fulcrum centerline down a good .250" +

Chasing a perfectly centered swipe pattern isn't all it's cracked up to be.. millers mid lift theory says the same thing.. you can be quite a bit off the center of the tip, as long as your at the 90deg point at mid lift.
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Re: Rockers too high on the studs?

Post by treyrags »

travis wrote: Mon Dec 30, 2019 11:04 pm What I meant by "looking too high" is that the rocker, even with the "proper" length PR for this setup, is still sitting too far up on the stud.

I've already got the head off and everything masked for paint, so no more pics at the moment.

Out of curiosity, I drug my last remaining sbc out from under the bench, stuck a 305 head on the short block, and mocked everything up with these rockers. Everything looks perfect with a stock length sbc pushrod. So, it appears to me that everyone who said this was an sbc rocker, was correct.
If you don't have thread engagement in you rocker nuts of at least 1.5 x the diameter of the stud you need longer studs.
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Re: Rockers too high on the studs?

Post by Paul Kane »

SchmidtMotorWorks wrote: Sun Dec 29, 2019 5:32 pm The pivot level should be about 1/2 of lift below the valve tip, measured along the axis of the valve.
JohnsMistake.jpeg
So, your pushrod is way too long.
John, this is erroneously drawn. The imaginary red line to the tip of the rocker arm should reach the roller wheel's axle, not the radius of the roller wheel.

One of the (multiple) purposes of the wheel is to help the rocker maintain ratio as it travels through its radial sweep. Your drawing is for a shoe-tipped rocker arm whose arc will diminish (increase ratio) as the valve opens and tighten (decrease ratio) as the valve closes. The red line drawn in this picture should go to the center of the roller axle.

(Not trying to single you out, I want to use this as an educational tool for others. :) )
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Re: Rockers too high on the studs?

Post by Paul Kane »

travis wrote: Mon Dec 30, 2019 3:18 am In the photo, the valves are closed.
Travis then your 8.00" pushrod is way too long as evidenced by the geometric angles with the rocker at rest/closed, and as extrapolated therefrom if opened halfway and at full lift:
BSRockerSetup.jpeg

As seen above, the rocker arm is already over-arcing on the pushrod side and it isn't even opening the valve yet.
travis wrote: Sat Dec 28, 2019 10:39 am It doesn’t seem to matter what length I set my adjustable pushrod measuring tool at...each time the tip pattern is nice and tight it isn’t in the center...
Forget where the roller tips rests atop the rocker arm--that has nothing to do with valve train geometry. Instead, concern yourself with the geometric angles of the rocker arm, valve, and pushrod. The location of the roller wheel atop the valve stem is essentially inconsequential and depends on all kinds of things such as rocker arm design, rocker arm dimensions, valve angle, valve length, rocker stud location, etc, etc, etc, not necessarily the valve train geometry.
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Re: Rockers too high on the studs?

Post by turbo camino »

Are we still discussing how to set proper geometry for SBC rockers on a SBF? There is no pushrod length that will compensate for a rocker that is too short from pivot to tip.
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