Different geometry with swivel feet?

[skyto]

[modok]

HEY BUDDY!! WHERE YOU BEEN???
been hiding between the lines? ok
Whatever, welcome back!

Well you know, those scat rockers were designed by nascar monkeys.
You feel free to explain what those monkeys were thinkin' if you can relate


We got the stock rockers+ swivels pretty well figured out. So if you want variable ratio or what not at least a guy can see what's going on.

[nsracing]

What are you two sleeping together? How are you fellas??

As I re-read through this crap, I just realized we did not even have a "cam profile" Mr. Skye here is trying to accomodate w/ these swivels feets. I hope this cam is not designed for 1.4 ratio rockers.

Yes, you have to watch how the swivel can hit the "neck" of the ball when you adjust the geometry to "straight up" at full lift. I found that for stock cams and Engle 100 or 110, there is not hitting or binding w/ the swivel to the neck of ball.

And also true, the NASCAR geometry is for roller rockers from its article, I applied that to our VW rockers..wiper styles and rollers w/ the rigid adjusters in the back (pushrod end). Adjuster and pushrod is straight up at full lift.

With the Porsche or Berg swivel if you attempt to do the above, then sure you have to check for swivel vs. neck of ball binding. What I do is "slightly over" not straight up at full lift because of this swivel bind. I did mention in the earlier post. But neglected to explain further. sorry.

And this is for Mr. Skye. It is nice that you are measuring all the angles. And you have found that the angles are the same on valve end and pushrod. Come on man. The rocker is 1:1 ratio. Of course the angles are gonna be the identical. You cut a pie in half, don't you think you are gonna find identical cheeks?

Not busting your bubble at all. It is all part of learning. Very commendable effort. Very cool.

Lastly Skye, I do not like shims. Just more to worry about. So I do not use them. Here is my way to not use them. With the Swivels, you can cut the pushrod shorter to give the proper geometry. If you find that you need clearance because the swivels bottom out, you can grind under rocker to "cup" an area for the swivel to clear. This is my "swivel secret" information you can do as you please w/ using no shims, and making the swivel straight up w/ valve at full lift.

Enjoy.

[modok]

Thumbs up to skyto!
When the math lines up with reality, then you know you are seeing clearly. Dispite the hangover!

i agree, NSR was talking about wiper or roller rockers, he should have made that a little more clear.

[Dougy Dee]

Nick's Nascar method may somewhat work with wiper style or adjjuster at pushrod end rockers but larger lift and swivels will have the swivel assembly binding and screwing up. Swivel feet I always go to 1/2 lift strait up. Wiper style it's about the pattern across the lashcap face.

[skyto]

What a hangover. Thought I'd double check the geometry afterwards by calculations. The same thing was explained in different words here and here.

checking by calculations

At the start the geometry was at factory default settings (nos 40hp engine).

With stock cam and 1:1 rockers, the average lift is 7.54mm intake / 7.25mm exhaust.
After all the mods and pushrod adjustments the lift ended up being 8.77 intake / 8.32mm exhaust.

- the lift increase is 1.15mm on average, so the shaft should be lowered by 0.575mm to get the geometry back to original.
- a stud repair kit and later style rocker blocks were installed. Without shims, the shaft ended up being 0.2mm higher than before.
- the swivel foot pivot point was 4.5mm from the bottom surface. That's effectively a 4.5mm addition to the valve stem height. The shaft should be shimmed higher by the same amount.

Theoretical shimmage needed to get back to factory geometry:
4.5 - (0.575 + 0.2) = 3.725mm

That's suspiciously close to my previous results with the available shim thicknesses: 3.73mm. Almost as if I had fiddled the numbers. It all points out that the swivel foot turn radius adds to the geometric height of the valve stem. When installing ratio rockers at the same time, the need for extra shims would be

(swivel foot turn radius - (ratio rocker lift increase / 2))*1.01

This applies to stock geometry, in situations when the geometry was set right with stock parts before modifications.

Edit: the valve angle correction factor is roughly 1.01 for both older 9 and newer 9.5 valves. This would change my result to 3.76mm.

[slingblade]

really good camera there,,enjoyed this topic

[modok]

Wow, well done. That's .145" of shim to us Americans.
I love the lift graph, that really proves the point.
So if you had an engle 110 you would need more like .090" (2.3mm) shims, interesting.

[ALB]

[bigbore]

I haven't looked but do thay make longer rocker shaft stud's? from what I have seen after shiming theres not enuff stud to get the nut on with full threads.
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[skyto]

Here’s the result with 3.73 mm shims. This seemed to be the near correct shimmage in terms of lift and adjuster foot movement. I used photoshop to find the parallel adjuster & half lift situation.

Watching the foot part alignment was also helpful here.

With parallel adjuster at half lift, the geometry coincided with the pivot points of pushrods and swivel feet. The practice of aiming at the valve tip when using swivel feet seems to be questionable.

I haven’t cut the pushrods yet. If you think I’ve got it all wrong, bring on the facts please asap- the archery cutter will be available next week.

[skyto]

Here’s the lift data with different sets of shims. For each shim pack I adjusted the pushrod length n times, searching for the highest possible lift. This never happened with parallel adjuster at half lift, the thing was just to find out the lift potential in each case. Only repeatable results were written down. Differences are small, but there might be some gain around 3.4-3.8 mm.

[skyto]

3.73mm shims. Here the adjuster moves hardly at all. Zero and full lift swivel foot positions look about identical. This means near correct shimmage when going for stock geometry.

The adjuster is not centered on the stem, but that’s entirely my own fault. I used eccentric rocker studs– adjusted them for the 1.45 mm shims that came with swivel feet, and glued them in with green loctite. Reason was that the contact point was too low then. Now it’s too high.

[skyto]

Here’s the situation with 4.56mm shimmage. Sorry about the last foggy pic, but hope you can see that the foot is at it’s lowest at full lift. It moves downwards on the valve tip while lift increases. The shaft is shimmed too high.

[skyto]

Finally had the time to return to this. Tried to find out if excessive shimmage is really needed when using swivel feet. Most people use the shims that came with the adjusters, but in this case they didn’t do no good.

With no shims at all, zero lift angle was too much for the adjusters. So more shims were added.

Here the shaft is shimmed 2.28mm higher. Surprisingly the adjuster foot moved upwards on the tip all the time while going from zero to full lift. This meant the shaft is still too low.

[modok]

True, but keep in mind the spring force is NOT the biggest force. I am not making this up.
The opening and closing rams at high rpm is where the max forces will be through valve train.
Have a look at some of the SAE papers where they map actual valve travel running verses static. As low as 2/3 of max design rpm the valve floats clear over most of the nose of the cam and then "lands" somewhere like 2/3 lift, then kinda bounces the rest of the way through the closing ramp. This is seen to some degree even in overhead cam engines. Turns out that everything is springy when you get down to it!
The instantaneous forces at the main part of the opening ramp and the force of the landing and bounce on the closing ramp are far greater than your spring force.

So the 90deg. at full lift is a good idea for trying to putter around low rpm with super strong valve springs, if thats what you like to do, but I don't know what it has to do with nascar. Perhaps they are using insane "parts breaker" cam profiles designed to take advantage of lofting the valve?? That would make for a pretty "hard landing" somewhere in the rev range!

[cptcliffhanger]

1 other argument that could be made for "NASCAR" (I never heard it called that before) geometry is that as the valve approaches full lift, the push-rod gets closer to 90 degrees which affords it more leverages as the force increases. this could arguably reduce the overall compression forces that the push-rod sees.. possibly... I have not run the nubers..

S

[jakeddy]

hmmm... thinking out loud, possibly even at 3/4 lift then? as a compromise.

[cptcliffhanger]

there is some logic to this so called "NASCAR geometry".. Madoc, you mentioned it's just vectors and you are right. a vector is a force and a direction. the idea it to make the direction (in this case we are mostly concerned with the side loads that are imposed onto the valve stem) closest to zero while the load is the greatest (load is provided by the spring which is of course the greatest at full lift) .. Not sure how to word it better than that (sorry)..

the theory is is to minimize the sideloads on the valve stem to try and save the valve guids. some argue that to do this you should set the stem/rocker angle to 90 deg @ full lift so that as the spring pressure increases the side load decreases (all the way to zero side load when the arm is at 90)

S

[bigbore]

I have checked mine many times for fit ( I use the ball type ajuster's) the cam's I ues are stock or a little hot ( 100 or 110) and thay hit just right on the valve stem. I cut 1/8 inch off the stock push rod and thay come out right on no shim's no grinding. At mid push thay are right in the middle of the stem. It maybe becouse I use stock or mostly stock cam's.
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