Explain ADJUSTABLE ROCKER ARMS to me.

[Oldtimer]

Starting to purchase parts to rebuild 351W.
AFR recommends Scorpion roller rockers for heads with 3/8 stud mounts.
Scorpion says We only have adjustable in Endurance series and 5/16 pedestal mount.
Scorpion roller rockers come with polylock nuts, which by definition are, an adjustable rocker arm nut.

How can a 3/8 stud mount roller rocker with a polylock nut NOT be adjustable?

 

[bronco italiano]

I just looked at their site. They do have 3/8 non-adjustable in endurance. If you are going high lift cam I would want the stud support to be at least 3/8"

 

[Oldtimer]

If it is non-adjustable, don't you just torque the nut against a solid stop?
Why include polylock nuts?

 

[bronco italiano]

You have to measure for rod length.

 

[73azbronco]

Hydraulic lifters? Never heard of adjusting hydraulic lifters. But, make sure pushrod length is right.

 

[bmc69]

Hydraulic lifters? Never heard of adjusting hydraulic lifters. But, make sure pushrod length is right.

Very common to have an adjustable valve train with hydraulic lifters when using roller rockers, aftermarket cam, etc. Of course, up to about 1967, the factory 289 rockers were adjustable.

 

[DirtDonk]

Every old school Chevy rocker arm I ever saw was adjustable. With six cylinder or eight, it was fully adjustable from the factory.
First time I ever saw non-adjustable rocker was on a Ford.

 

[jamesroney]

Starting to purchase parts to rebuild 351W.
AFR recommends Scorpion roller rockers for heads with 3/8 stud mounts.
Scorpion says We only have adjustable in Endurance series and 5/16 pedestal mount.
Scorpion roller rockers come with polylock nuts, which by definition are, an adjustable rocker arm nut.

How can a 3/8 stud mount roller rocker with a polylock nut NOT be adjustable?

Put your Scorpion Endurance roller rocker on a 68-79 Ford Positive stop factory head. It has a rocker stud with a 3/8 shoulder, and a 5/16 thread. In order to make a bolt on solution, Scorpion had to duplicate the geometry of the original fulcrum. It uses a 3/8 stud mount rocker, but the polylock goes in the trash can.

So the Endurance series is smaller, lighter, and shorter than the Race series. But more important, the roller end undercut is smaller. So the race series can handle a 1.625 valve spring, but the Endurance cannot. Also, the valve covers need to be taller. Which is a problem for EFI plenums, and baffled valve covers.

 

[Oldtimer]

So . . . the title of this thread should have been different, but I didn't know what I didn't know. And now I probably know less

I was struggling with pivot point locations in rocker arm geometry.
The internet says to adjust push rod length so that roller tip rub mark is in center of valve stem. With a "adjustable" rocker arms on stud mounts, the fulcrum of the rocker arm is a moving target, and the internet ignores this fact.
They refer to adjustment when setting pre-load on hydraulic lifter (zero play + 1/2 turn), but don't mention the pivot point for the fulcrum, which obviously affects the OAL of the push rod.

I stumbled across an excellent article on Rocker Geometry by Jim Miller (attached below) that explains the ins and outs of rocker geometry.

The Director of Operations at Scorpion was correct in stating their rocker arms are not adjustable, in relation to the rocker fulcrum point, the push rod length establishes this.
The rocker arms are adjustable in that you can adjust pre-load on hydraulic lifter and lash on solid lifters. . . I think?

James,
Thanks for pointing out undercut differences on Race & Endurance series of lifters.
Scorpion makes no mention of this, and I suspect it was a learning experience for you.

 

[DirtDonk]

Explain what you mean by “the fulcrum is a moving target” because I’m not quite grasping that.

A rocker arm ratio rating assumes a fixed pivot point. The fact that the arm rotates on that fixed point, doesn’t change the location of that fixed point, or the distance between pushrod and valve tip.
And that same fixed point is hard mounted to the cylinder head. So the distance between the push rod pocket and the roller tip doesn’t change.
But the “height” at which the rocker arm is riding on the stud (or height above the cylinder head), is what changes where the roller tip touches the valve tip. Think triangles…
This height is what the length of the push rod effects.
I think…

 

[Oldtimer]

A stud mount rocker arm will move up and down on the stud.
Aftermarket heads (the ones I am looking at) don't have a hard mounting point for the rocker arm.
Yes the distance between push rod pocket and fucrum point is fixed, so is distance between roller pivot and fulcrum point.
With a non-hard mount rocker arm, the nut on the stud needs to be set so that the angle of the fulcrum pivot to roller pivot axis and the valve stem axis is 90 degrees, at the MID-LIFT position (half open).
Once that is established, the length of the push rod can be determined.

Jim Millers article talks about Design geometry which is determined by the manufacturer, and Intall geometry which is determined by the mechanic.

 

[DirtDonk]

Interesting rocker arm. I’d forgotten about those with adjustable push rod sockets. Never used one, so I didn’t have it in my mind.
That simply changes the effective length of the push rod to help with the geometry, correct? Get it a little off with the pushrod length and you can fine-tune it. Pretty cool.
But that’s not the “Scorpion” type you’re referring to, is it?

That particular one is a shaft (trunnion?) mount? Or individual shaft mounts, like you’d see on a canted valve head? Or Is that what you meant by pedestal mount?
That’s not what I had in mind with different pedestal mount designs that I’ve seen from the factory.

When you say that the heads you’re interested in, don’t have a hard mount for the rocker, you mean that it’s just got a threaded hole for a stud, correct? That’s still a hard mount, I believe. Just maybe not the way you’re thinking of it.
The adjustable rocker on a stud is hard up against three points. The push rod, the valve tip, and the pivot point against bottom of the adjusting nut.
That’s still a hard mount. No?

It can pivot/rotate side to side on a ball-n-socket pivot, changing the action. But that’s why most adjustable valve trains have pushrod guide plates.
A pedestal mount has the rocker arm pivoting on a “barrel“ (a really big roller bearing?) so to speak. Letting it rock back-and-forth, but keeping it from pivoting side to side.
Do the AFR heads come with studs and guide plates? Or do you have to source everything separately?

Sorry if I’m still missing the pitches that you’re throwing. Just trying to see what the concern is that you have.
Sorry, but I also haven’t checked out the PDF you posted yet. I’ll do that when I get back to the computer.

Bring a cylinder head and valve train with you to the restaurant and we’ll toss it around at the table!
See how I worked a Bronco lunch into the mix there?

 

[Oldtimer]

The rocker arm photo I posted was just to show valve stem angle to roller-fulcrum axis.
Hard mount to me is torque nut/rocker against a shoulder. Adjustable mount is turn nut until play is gone, and lock in place.
Will come visit for lunch, but will not order parts till I understand how deep a hole I am digging.
Yes, AFRs come with studs and guide plates.

 

[73azbronco]

A stud mount rocker arm will move up and down on the stud.
Aftermarket heads (the ones I am looking at) don't have a hard mounting point for the rocker arm.
Yes the distance between push rod pocket and fucrum point is fixed, so is distance between roller pivot and fulcrum point.
With a non-hard mount rocker arm, the nut on the stud needs to be set so that the angle of the fulcrum pivot to roller pivot axis and the valve stem axis is 90 degrees, at the MID-LIFT position (half open).
Once that is established, the length of the push rod can be determined.

Jim Millers article talks about Design geometry which is determined by the manufacturer, and Intall geometry which is determined by the mechanic.


View attachment 938568

this is correct, thats why when you step away from stock, you need to verify proper pushrod length. I should not have said never on adjustable, I just have not used them. I rely on proper pushrod length to solve the issue and its one less part to fail or go out of adjustment.

 

[bronco italiano]

You are near 904 Bronco. May be best to just pay him to set it up while you watch/learn. Rocker arm geometry can be very confusing.

 

[Broncobowsher]

I've been playing mind games about this for over 30 years. The rocker arm travels in an arc. Valve opens linear. The way I have figured it is the rocker tip should (but rarely does) do a double swipe of the valve tip during the open, and again during the close. That perfect perpendicular between the pivot, tip and valve stem should happen at mid-lift. That would be the tip of the rocker the furthest away from the valve stem. Above and below mid lift (closed and open) the arc of the rocker will suck the tip in slightly closer to the rocker arm stud.
If you look at a 2nd gen hemi, the exhaust rocker is extremely long. This is great. For a given amount of lift the rocker has very little arc travel and very little sweep across the valve tip. But the valve covers are huge and there really isn't a good way to change the stud to valve stem distance. So we are stuck with short rocker arms. In order to get those short arms to have a lit of lift, there is a lot of rotation on the pivot. That greater arc travel runs the rocker tip further across the valve tip. If you really want to get into the geometry games, a non-roller tip rocker, properly engineered and installed, can work to keep the contact point nearly perfect on the center of the valve. By shaping the contact surface so the contact point moves as the valve opens. Back to the mind games of the past 30 years, that correct geometry also results in a variable ratio rocker arm. The more the rocker is opened, the greater the rocker ratio. But the friction of the rocker tip on the valve tip creates side loading of the valve guide as it cycles. Thus the roller tip has an advantage of reducing friction and wear of the valve in the guide. The shorter the valve guide, the greater the lift, the stiffer the valve spring, the greater benefit there is. So a roller will have more swipe across the valve tip since it can't very the ratio as it cycles, it isn't actually side loading the valve as much since it is rolling and not sliding.

Oh the mind games and horrors of rocker arm design. Then I saw an engine where the cam lobe didn't rotate, it oscillates. the valve opens on the ramp, the ramp stops and back up letting the valve close. Then the computer plays with how far up the ramp the valve goes before it backs down. Variable lift, variable duration (the two have a fixed corrolation) and the cam is on a phaser so the timing can be doctored as well. That stuff makes the pushrod engine really simple.

As far as the adjusters on the rockers, ford's first overhead valve V8 (and matching architecture I6) used that design. Somehow I have owned too many of engines. With a fixed shaft rocker arm, the only place left for an adjuster is the rocker arm pushrod pivot. Because you don't want to get into the flat head design where you have to remove the intake manifold in order to adjust the valves at the lifter itself. And while at wacky valve adjusters, some Mitsubishi 2.6 heads had the hydraulic adjuster at the tip of the rocker where it contacted the valve tip.

Way too much typing and ranting tonight. Probably way over confused now as well.

 

[Speedrdr]

Well, damnit! Here I was thinking I had a working grasp of valvetrains and their operation.

I KNOW NOTHING!

 

[bmc69]

As far as the adjusters on the rockers, ford's first overhead valve V8 (and matching architecture I6) used that design.

Many FE engines and all SD engines had the rockers with the adjustable pushrod ball. Of the many FE engines I've built over the years, nearly all were converted to the adjustable rockers if they were not already built that way. I'm also right in the middle of setting up the rockers on a set of heads for a 533 Ford stroker I'm building. In the picture, all ready to set on the engine and determine correct pushrod length.

 

[Broncobowsher]

Many FE engines and all SD engines had the rockers with the adjustable pushrod ball. Of the many FE engines I've built over the years, nearly all were converted to the adjustable rockers if they were not already built that way. I'm also right in the middle of setting up the rockers on a set of heads for a 533 Ford stroker I'm building. In the picture, all ready to set on the engine and determine correct pushrod length.

I was thinking Y-block. Strange thing, I somehow have never owned an FE engine. I remember them growing up. Owned many small blocks, 385 series. Y-block and a couple of 233s (or were they 223s?), whatever the straight six version of a Y-block was.

 

[jamesroney]

"That perfect perpendicular between the pivot, tip and valve stem should happen at mid-lift."

Going to disagree. I'm pretty sure the "perfect perpendicular" should happen at the point where the load is maximized, and therefore should occur where the valve spring load is highest. The highest spring force occurs at maximum lift, and that is the point where you want to optimize.

If you want to build the most stable valve train geometry, the roller tip contact line would be exactly centered on the valve stem at maximum impulse. As an example, a high performance spring seat pressure might be 200 lbs, and the open pressure might be 450 lbs. The load (and impulse) at max lift is vastly larger than the impulse anywhere on the ramp.

The only reason to center the rocker tip at mid-lift is if you sell camshafts (or rocker arms) and you don't want to do any actual engineering. It's "safe."

Anybody can hop around on a pogo stick with one leg. But if you want to maximize your height on a pogo stick, you want both feet on the pegs when you hit bottom.