Rockers too high on the studs?

[Paul Kane]

Are we still discussing how to set proper geometry for SBC rockers on a SBF?

A rocker arms does not know which manufacturer affiliation it is assigned--hell, even rocker arms from various manufacturers, all of which are intended for a specific engine (ie, all of them made for an SBC), have geometric design differences between them. And so we are simply attempting to best optimize the valve train geometry given the components with which we have to work. At least that's how I'm attempting to help.

Now if the OP changes rocker arms, then the process starts over again. That being said, I think these rocker arms can be made to work adequately...they may not be not ideal by my personal standards but they can nonetheless be set up to provide more efficient transfer of cam information than most setups I often come across in the wild.

There is no pushrod length that will compensate for a rocker that is too short from pivot to tip.

A rocker arm that is "too short from pivot to tip" does not in-and-of-itself have any say whatsoever on pushrod length--let alone rocker arm geometry as a whole--since that dimension alone is only a piece of the equation. Incidentally the nominal, dimensional difference from trunnion-to-roller tip between the SBF and SBC rocker is 0.060", where the Ford rocker [for the SBF 20-degree head] would be 0.060" long relative to the SBC rocker [for the SBC 24-degree head].

[Paul Kane]

The roller tips look real big.

Yes, absurdly so. The roller wheel on the tip of a roller rocker should be as small as is physically possible. Ideally, the radius of the roller wheel should be the same as the radius of the pushrod cup.....but usually that isn't physically possible.

Most manufacturer's don't even know the purpose of the roller wheel in the first place--most seem to think it's there just for "friction reduction," which is the very last reason it's there...and "friction" probably isn't even considered by those manufacturers who better understand the purpose of the wheel.

[midnightbluS10]

The roller tips look real big.

Yes, absurdly so. The roller wheel on the tip of a roller rocker should be as small as is physically possible. Ideally, the radius of the roller wheel should be the same as the radius of the pushrod cup.....but usually that isn't physically possible.

Most manufacturer's don't even know the purpose of the roller wheel in the first place--most seem to think it's there just for "friction reduction," which is the very last reason it's there...and "friction" probably isn't even considered by those manufacturers who better understand the purpose of the wheel.

PBM calls them "oversized nose roller for superior load distribution".

[SchmidtMotorWorks]

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. )

If your goal is mid-lift, to minimise the width of the contact patch you are correct, it should be as the image below:
MID LIFT

midlift.PNG

If you want to have higher oil entrainment and the contact point to be on center (depending on rocker arm), then the pivot point should be about 0.200" lower on most heads.
Current OEM designs typically have the pivot below mid-lift, both rollers and sliding contacts last longer with higher oil entrainment.


LOW PIVOT

low_pivot.PNG

When I was at Edelbrock we designed a valve-train for an engine with an extraordinarily highly-stressed valve-train, We had it simulated and optimised in GT Suite. Generally, we found that the optimum pivot level was below mid-lift and the contact on-center at maximum lift.
The crossover in the optimization is between entrainment velocity and sliding distance.
https://www.gtisoft.com/valvetrain-mode ... -gt-suite/

[SchmidtMotorWorks]

The roller tips look real big.

Yes, absurdly so. The roller wheel on the tip of a roller rocker should be as small as is physically possible. Ideally, the radius of the roller wheel should be the same as the radius of the pushrod cup.....but usually that isn't physically possible.

Most manufacturer's don't even know the purpose of the roller wheel in the first place--most seem to think it's there just for "friction reduction," which is the very last reason it's there...and "friction" probably isn't even considered by those manufacturers who better understand the purpose of the wheel.

PBM calls them "oversized nose roller for superior load distribution".

The larger diameter (radius) reduces contact stress, makes it last longer.
Some nitro rockers have very large tip roller IIRC about 1" to control contact stress.

[Geoff2]

I believe Jon Schmidt's original drawing is correct [ with red, blue, yw lines ]. What matters with a roller rocker is the contact point of the roller tip on the valve stem tip. The ratio on the valve side of the rocker is from the distance from the c/l of the trunnion to the point of contact of the roller on the stem tip. This distance changes during operation. The roller tip axle centre is irrelevant for valve side geometry, only relevant in determining the nominal rocker ratio & pushrod cup location. Imagine that for some reason that the roller tip locked solid, would not rotate. The valve action would be the same, although the roller would be skidding on the stem tip & wear would occur. It would be acting like a stamped rocker with a shoe radius equal to the roller diameter.

[gmrocket]

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.

If it was too short, then how is his sweep and contact point on the valve top centered with multiple p Rod lengths?

Seems that side is pretty good

[gmrocket]

Yes, absurdly so. The roller wheel on the tip of a roller rocker should be as small as is physically possible. Ideally, the radius of the roller wheel should be the same as the radius of the pushrod cup.....but usually that isn't physically possible.

Most manufacturer's don't even know the purpose of the roller wheel in the first place--most seem to think it's there just for "friction reduction," which is the very last reason it's there...and "friction" probably isn't even considered by those manufacturers who better understand the purpose of the wheel.

PBM calls them "oversized nose roller for superior load distribution".

The larger diameter (radius) reduces contact stress, makes it last longer.
Some nitro rockers have very large tip roller IIRC about 1" to control contact stress.

And allows for a larger axle which creates more contact area between the body and axle.. = higher load capability

[SchmidtMotorWorks]

I believe Jon Schmidt's original drawing is correct [ with red, blue, yw lines ]. What matters with a roller rocker is the contact point of the roller tip on the valve stem tip. The ratio on the valve side of the rocker is from the distance from the c/l of the trunnion to the point of contact of the roller on the stem tip. This distance changes during operation. The roller tip axle centre is irrelevant for valve side geometry, only relevant in determining the nominal rocker ratio & pushrod cup location. Imagine that for some reason that the roller tip locked solid, would not rotate. The valve action would be the same, although the roller would be skidding on the stem tip & wear would occur. It would be acting like a stamped rocker with a shoe radius equal to the roller diameter.

Some "skidding" is actually desired and most of it should be in one direction.
The sliding entrains an oil film between the surfaces.
If there is not enough sliding it dries out.
One a roller tip, it makes the tip rotate in one direction.

As the sliding velocity increases the friction (and wear) decreases.

[gmrocket]

I believe Jon Schmidt's original drawing is correct [ with red, blue, yw lines ]. What matters with a roller rocker is the contact point of the roller tip on the valve stem tip. The ratio on the valve side of the rocker is from the distance from the c/l of the trunnion to the point of contact of the roller on the stem tip. This distance changes during operation. The roller tip axle centre is irrelevant for valve side geometry, only relevant in determining the nominal rocker ratio & pushrod cup location. Imagine that for some reason that the roller tip locked solid, would not rotate. The valve action would be the same, although the roller would be skidding on the stem tip & wear would occur. It would be acting like a stamped rocker with a shoe radius equal to the roller diameter.

Some "skidding" is actually desired and most of it should be in one direction.
The sliding entrains an oil film between the surfaces.
If there is not enough sliding it dries out.
One a roller tip, it makes the tip rotate in one direction.

As the sliding velocity increases the friction (and wear) decreases.

Yep, the thought that the wheel rotates back and forth as it travels up and down , does not happen.

For one, at upper upper rpm's. There isn't enough time to rotate back and forth, if you have that happening, you have major friction between tip and wheel . It skids on the return to seat journey, and will rotate/skid on the opening

[MadBill]

I believe Jon Schmidt's original drawing is correct [ with red, blue, yw lines ]. What matters with a roller rocker is the contact point of the roller tip on the valve stem tip. The ratio on the valve side of the rocker is from the distance from the c/l of the trunnion to the point of contact of the roller on the stem tip. This distance changes during operation. The roller tip axle centre is irrelevant for valve side geometry, only relevant in determining the nominal rocker ratio & pushrod cup location. Imagine that for some reason that the roller tip locked solid, would not rotate. The valve action would be the same, although the roller would be skidding on the stem tip & wear would occur. It would be acting like a stamped rocker with a shoe radius equal to the roller diameter.

Partially right, but it must be specified that the referred-to distance is along a line at a right angle to the valve stem, not sloping down to the tip contact point. Since the contact point of the roller on the valve will always be directly below the axle (that is, on a line parallel to the valve stem), it is the arc the axle follows as the valve opens that defines the roller contact point on the tip and thus the momentary effective length of the valve side of the rocker. If the roller was locked, the contact point would move differently vs. the free-rolling case as the valve opened, slightly changing the geometry.

[MadBill]

..
Yep, the thought that the wheel rotates back and forth as it travels up and down , does not happen.

For one, at upper upper rpm's. There isn't enough time to rotate back and forth, if you have that happening, you have major friction between tip and wheel . It skids on the return to seat journey, and will rotate/skid on the opening

As with solid roller lifters discussions, the rationale re spin/skid ratios for roller tip rockers is compelling, but AFAIK, data is lacking. With all the high speed photography and strobe videos on the net, surely someone has posted one showing roller tip action in sufficient detail to make or break the case?

[Kevin Johnson]

..
Yep, the thought that the wheel rotates back and forth as it travels up and down , does not happen.

For one, at upper upper rpm's. There isn't enough time to rotate back and forth, if you have that happening, you have major friction between tip and wheel . It skids on the return to seat journey, and will rotate/skid on the opening

As with solid roller lifters discussions, the rationale re spin/skid ratios for roller tip rockers is compelling, but AFAIK, data is lacking. With all the high speed photography and strobe videos on the net, surely someone has posted one showing roller tip action in sufficient detail to make or break the case?

You can see the wheel rotate.

[travis]

One BIG brain fart I did when checking with the PBM rockers was not accounting for the lifter plunger collapsing (too many distractions), so any previous numbers was basically garbage...

With the Scorpion rockers in place, using the Straub method mentioned earlier in this post, at .272" valve lift (1/2 max lift), I get a length of 7.750" when testing in .050" increments. But...there is also the lifter plunger bottomed out which is 2 1/4 turns down from 0 lash, which on a 3/8" stud calculates to .0945". So...7.700" should be about right, correct?

[FC-Pilot]

One BIG brain fart I did when checking with the PBM rockers was not accounting for the lifter plunger collapsing (too many distractions), so any previous numbers was basically garbage...

With the Scorpion rockers in place, using the Straub method mentioned earlier in this post, at .272" valve lift (1/2 max lift), I get a length of 7.750" when testing in .050" increments. But...there is also the lifter plunger bottomed out which is 2 1/4 turns down from 0 lash, which on a 3/8" stud calculates to .0945". So...7.700" should be about right, correct?

Now I feel bad as I was wondering about that and did not speak up. We all have missed stuff before. I just feel bad as we often can get back on track sooner when someone kindly helps us find our error. The pushrod should be longer as your rocker needs to maintain its position and a longer pushrod will compress the plunger while holding the rocker in its proper location. Or are you saying you did your updated measurements with the lifter bottomed out and now need to shorten the pushrod to allow the plunger to rise from the bottomed out position? I am guessing that the 2 1/4 turns down is .945 and not .0945. If that is the case and you do need a shorter pushrod then I would shorten it to a 7.65 or shorter (depending on what the lifter manufacturer calls for preload).

With hydraulics I figure out where the rocker needs to be for proper angles (Sweep), then with it set at the proper angle resting on the lifter (the plunger not depressed) I measure what the pushrod length is and then add what I need for proper preload. That way I get my rocker where I want it and then make sure the lifter gets what it needs and then I am done. (If that does not make sense, sorry. Having a migraine and trying to explain my procedures while sleep deprived and in pain may lead to errors in my explanation). LOL

Paul