Pushrod Length, best method

[Wolfplace]

But try running that Chevy/ Crane guy's method at high rpm with a big cam and...

Did I miss something?
I have no idea what you are saying????

[MadBill]

Joke! (I hope...)

[wyrmrider]

look at the other videos on the right of the one we are talking about

[77cruiser]

look at the other videos on the right of the one we are talking about

Only 20 of them there should we just pick one & go with it.

[wyrmrider]

More than that
Getting hung up on the pretty girls?
use the process of elimination and come up with a very few
like
https://www.youtube.com/watch?v=RjaosX63DkM

[randy331]

http://www.youtube.com/watch?v=UBO-Mgp0Og8

There's a lot to learn on youtube!!

Randy

[MadBill]

Don't like to gore anyone's ox, but I have a few problems with the (upper) Crane/Ralph Johnson vid.

First, it implies that a 0.150" longer pushrod is likely to noticeably improve geometry and increase the effective ratio. In reality, the selected cam has 0.417" lobe lift, far more than what the OE gear was designed for (~ 0.260" lobe lift for for tens of millions of production SBCs), thus the former's base circle will be 0.417" -0.260" or ~ 0.157" smaller, requiring a like increase in pushrod length to compensate.

Second, there is no mention in this segment of the effect of above on contact location or width.

Third, it assumes that the only purpose of changing PR length is to maximize valve lift. This may be true for stock and many milder aftermarket cams and gear, but for a serious engine, the much greater targeted lift will be arrived at by rocker ratio, cam journal diameter and lobe lift selection, without accepting any compromises re side load-inducing geometry.

Fourth, in part 2., in contrast to the words, the contact patch shown appears to be running right off the valve tip.

Lastly, although a narrow contact zone (0.035") is suggested, no method for attaining it is offered.

PS: The checker tool in the second vid is better (just barely) than nothing, but could give a false sense of confidence...

[wyrmrider]

amen madbill
here's another forgettable one
https://www.youtube.com/watch?v=OmzbHgVY3cI
BTW we did use something similar to the Crane method with a stock non hp chevy cam in Stock class
made a few more hp, wore the valvetrain a bunch more (a 1/4 mile at a time no big deal)

[kirkwoodken]

Ralph Johnson is using stamped rockers. The valve side of the stamped rocker gets longer as the valve opens. The curved part of the stamped rocker tip moves across the valve stem as the valves opens. That does not happen with a roller rocker.

[steelcomp]

Sometimes pictures help:

[steelcomp]

90* geometry will yield minimum sweep, and minimum sweep will yield 90* geometry. One is a direct result of the other, and you can't have one without the other.

[steelcomp]

I liked the video too. I have never done it that way beither. the midlift 90 deg is the point of tangency to the valve line of action. this is the same thing that is accomplished with the narrowest wear pattern. By definition, the narrowest wear pattern is as near to tangency that can get.

Scott's method works very nicely, it is definitely less subjective. but in the engine compartment can be a little bit of a hinderance. I think I will head towards that method, or atleast a hybrid of the two. thanks for the doing that video.

The big question I get confronted with is how much off-center is really permissable. I can do engineering and eccentric load calcs, but often times people just want to know how close can you really get to the edge. Optimally, I say to break the valve tip diameter (not the valve stem diameter) into thirds, and try to stay within that middle third. But at the absolute max, into fourths, and stay within the middle two, but absolutely no more.

Its kind of spring coil bind. I have target values and I have absolute minimums.

I'll divide the valve tip into thirds. If the sweep pattern falls somewhere in the center third, I'm plenty happy with that. If it's on the edge of that third, I'll live with it. If it's outside that third, I think something should be dome to try and correct that.

[steelcomp]

the best durability and transfer of motion is when the valve's line of action (which may or may not occur dead-on the valve's centerline) is as closely aligned to the rocker arms sweep path as possible. In other words, the valve's line of action is tangent to the rocker's sweep arc. this is accomplished when the wear pattern is as narrow as possible (period). draw it out, with the multiple angles, and the narrowest wear pattern by definition occurs when the valve line action coincides with the rocker sweep path.

If this wear pattern location occurs too close to the edge of the valve stem, then some part of the set up has to be changed. rockers changed, valve heights changed, even lash caps can be used. But it does not change the fact that narrowest pattern is the best transfer of motion, it simply shows the asbuilt geometry cannot get there.

Wide wear patterns are from the valves line of action not being tangent to the rocker sweep. This really puts an off-axis load on the valve, even with a roller rockers. Draw out the sweep path and and lift envelope and alter the valve centerline angle to adjust the wear pattern path. You can easily notice the rocker arm is not pushing in line with the valve.

Only slightly off-topic, but how often do you find yourself having to choose between the perfect mid-lift pushrod length and the one which gives the most-centered stem tip wipe pattern?

Forcing a wear pattern to the center of a valve tip does nothing for geometry whatsoever. Ending up with the narrowest wear pattern and it happens to land center of the valve stem is perfection that can only happen if all the pieces fall together exactly perfect; a rarity. Hower, centering a wide wear pattern on the center of the valve stem is possibly a recipe for disaster.

If things just dont work, there may be a wrestling match between the narrowest pattern and the edge of the stem, but centering the wear pattern should not be part of the discussion.

Well put.
We are trying to convert radial motion to linear motion. In that radial motion there is a component of vertical movement, and a component of horizontal movement.
I look at the sweep as horizontal movement and I see horizontal movement = side loading. The least amount of horizontal movement = the least amount of side loading, regardless of location over the valve tip. We want maximum vertical movement, and minimum horizontal movement.

[wyrmrider]

"I'll divide the valve tip into thirds. If the sweep pattern falls somewhere in the center third, I'm plenty happy with that. If it's on the edge of that third, I'll live with it. If it's outside that third, I think something should be dome to try and correct that"

You do this drill AFTER you have correct geometry
changing the length of the rocker arm
moving the rocker shaft/ fulcrum back and forth- not up and down
moving the valve guide or tipping
if you are not too far off try a lash cap
but do not screw with your newly found pushrod length