Rocker Geometry

[raygreenwood]

I realize I am just talking pure pie-in thesky geometry here...so don't light me on fire (or at least piss on me to put me out ).....

.....but the real issue is how far off the exact centerline of the valve stem the rocker arm goes. Lets look at this from another perspective for a second.
I'm going to enlarge everything to make the point. If the valve stem were 1" indiameter and the rocker arm tip were only 1/4" in diameter....even if the swath it wiped across the valve centerline point were 1/2" wide....there would still be no appreciable side loading to the valve. It just does not get much outside of the centerline mass of the stem.
This is part of the reason why a swivel foot helps a bit. But even with a swivel foot....if you get too far out of centerline you are still dealing with a change in actual thrust angle....that pushes sideways.
One of the things I have always thought from looking at aside cross section of valve geometry (like you have in this thread)......is that as a total lift increases......the angle of the valve adjusting screw bore in the rocker arm (whether its swivel foot or conventional).....needs tochange to keep from increasing the inital thrust angle against the valve stem at both maxcimum lift and closed points.
This is the problem you get into quicker...when you use higher ratio rockers. the change in thrust angle of the rocker arm starts and ends at more of a tangent to the valve stem centerline than say a 1:1 ratio rocker arm would.

Is this making sense? Ray

[RockCrusher]

looks like your on track with your thinking.

RC
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[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[Desertbusman]

[hoghead]

I have read all 7 pages and see that someone else has my problem but no solution offered. I have new production Scat 1.25 rockers, adjustable at the valve end, using Mazda style flattened ball bearing tips. I have an adjustable push rod and dial gauge and spent the afternoon playing with them.

The problem is that I cannot get the rocker shafts low enough to bring the 2 centrelines parallel at 1/2 lift. Close but not perfect. Shimming the rocker stands only moves the bearing end further off centre, away from the rocker arm.

There are currently no lash caps, but if my addled brain has it right this will only exasperate my problem.
Correct?

While not in a rush to pull the new Steve Tims heads heads and get the rocker stands machined, I will if necessary.
I can foresee that machining in new o-ring seats will be a problem for the local shop

My nature is to get it right, and will do so if necessary, but how close is acceptable?

PS - I am assuming to start with the adjusters fully backed out (IE away from the valve) , less 1 turn.
Correct?

[Dougy Dee]

Think about it. Lowering the rocker stands is the same as raising the valve tip. Therefor lash caps should sort out your problem.

There are several sizes of lash caps, that add as much as .090" to the heights, so you can 'fine tune' your install.

[RockCrusher]

Yes for the adjusters. you can also machine or grind the underside of the adjuster end of the rocker arm to allow the adjuster to be raised further. Don't machine the stands except as a last resort. You need to lower the shaft or raise the valves. Lash caps will effectively raise the valves.

In the end, you will never get exactly what you want since the Scat rockers are not really correctly designed.
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[gerg]

I took about .010" off the back side of the 1.25s on my SC engine.
_________________
Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[RockCrusher]

[gerg]

Sorry, I meant .1" (one tenth)

I was using the 911 adjusters from AC.net and I believe it was John who reccomended it.
_________________
Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[mark tucker]

[gerg]

I've always read inline at 1/2 lift so you have equal sweep before and after inline (one reason). Raby's tech article goes to extreme lengths to stress finding absolute 1/2 lift for this.
_________________
Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[mark tucker]

so why do you want the most side or thrust at max lift????? I know raby thinks he is good,and yes he is pretty good, I know most everybody thinks he is god sun to berg.but what does that have to do with an thing? it also kinda depends on just what you are working on and what you have to work with. at 1 time I thought this was a good way to do it ,but then I started looking at what was happening,and how to make it better. and I consulted 2 major performance valvetrain manufactures (not copy cats) I had some very intresting sessions.and thus everything I have seen for the vw engines are junk,made wrong setup wrong, missunderstood, miss used..( no I have not had any pauter rockers in my hands & I do not know how there are set up or configured ) but thats what we have to work with .but there are ways to make them work better and make more power from the same engine combo.( I have ordered some new fixtures & tooling to make some rockers of my own) and no Im not trying to start a pissing contest so keep your pants ziped.and the eggo's in the toaster. how do you think we went from a spaceship crashing down from space into the ocean to a flying brick landing on a runway. well $$$ had a lot to do with it, and more thinkers& testing.

[gerg]

Well, I don't think person here is God.

I understood it had to do with equal sweep / loading through the entire range. You want the same angle at full lift as you do at no lift (minus lash), giving you alignment at 1/2 lift.

He's not the only person I've heard it from. And I am not spreading Gospel, just how I have done all of my prior engines that's all.

And props for continuing to test / adventure outside of what is common knowledge now. Maybe that is the way.

My pants were unzipped, but they are up now
_________________
Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[RockCrusher]

The theory is to have the least travel across the face of the valve stem and that equates directly to less guide wear. And there are 2 different rocker setups that do the job differently....OEM style in 1.1 and 1.25 and the adjuster over the pushrod style. The OEM style responds well to the 1/2 lift method and reduces sliding forces across the face even when the threaded adjuster is at an angle at full lift. It is force applied at a point tangent with and perpendicular to that tangent point straight down the stem with stock or swivel foot tips.

High ratio adjuster over push rod style are a different animal and due to the fact that most are designed wrong have a huge amount of slide at low to mid lift with less at high lift (less so on the 1.25). These need the lowest seated position or tallest valves to help minimize and equalize the situation while bringing the rocker closer to it's rated lift ratio. High mounting will increase the net lift but increase the slide distance and hence the side load and wear. Rollers would be the closest to ideal since slide load is absorbed in the roller trunnion rather than the side of the valve and guide.

RC
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[[email protected]]

we never landed on the moon, so what's your point?

[gerg]

So, is there more info available on setting up the rockers with the adjusters on the push rod end? My 1.25's are that style for the new engine.

My existing bus engine 1.25's have the standard VW adjusters - and I am pretty familiar with that process.
_________________
Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[RockCrusher]

On the standard style 1.25's pushrod length drive net lift. On the other type with pushrod adjuster you set the geometry independent of push rod length and allow that to determine what the length should be. Use the varying lash cap thickness's available to set the geometry if possible so you achieve correct lift. If ALL else fails, you can cut down the rocker stands. The last step is to then set the push rod length based on your results. During setup you will use an adjustable pushrod to compensate for changes in the valvetrain until you find the correct lift via lash caps or rocker tower trimming. Use a light spring on the valve for this work.

RC
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[mark tucker]

just shooting for "correct lift" dont make horse power, and dosent mean you are not side loading the valve. and as for the roller tip rockers they dont realy roll under load at speed, they mostly skid. and a roller can and will still pull (side load) on the valve. thus the movement to the non roller rockers like the mohawk style. but deferent profiles and deferent applications can make it hard to get just what you need. but with the foot type rocker on a lash cap, both are very hard and with proper oil the "side load" is very minamum as it glides across on the oil. thus you need the corect raidi of the foot and the proper hight of the rocker, most of the 1.4 rockers I have seen are or rather should be used with long valves to get the proper foot contact.and I would help if the shaft were farther down,possiably adding a second set of rocker stud holes could get it in the corect position. remember the valve angle? the longer the valve, the closer the tip gets to the shaft. there are many aspects of valvetrain system that most persons dont see and or cant understand what where when and why and how to remady it. you can put it just about any where you want it and it will work, most of the time it will work fine. but is it making the most power out of what is there??? I have changed the cam in my smallblock mopar in less than40 min from the time I pulled it in the shop till I pulled it out. I cant do that on my bug (I wish I could)so optimising the valve train is kinda importaint.but not for all. I wish I had the $$$ to have these systems built for me but I dont. the next time you build a motor and degree the cam in the engine make a graph(no not the long neck one )(and dont be drinken the long neck one either) make a chart of the lift and deg through the entire lift cycle at the valve for every ten deg. then add.100 worth of shims under the rocker blocks ( you will need some deferent length pushrods for this) and make another chart. then remove .200 from under the blocks( actuly -.100 from where you started in the first place.) ( you can simulate this by making an extra thick lashcap . ) you will need a short pushrod for this one. make a chart of the lift cycle now. then compair the findings. and forget about the max lift ,it dont mean shit. look at your .050 figures, the .020 figures the .070& the .100 figures. if you know any thing about cams & engines you will start to see something happening. can you figure it out?? a corectly made rocker can even do alot more than this and be easyer on the valve train. Ill stop hear before I overload somebodys brain. remember just because you cant see it or nobody told you 30 years ago about it dosent mean it isant there. and who said any thing about landing on the moon??? not me.

[hoghead]

On the standard style 1.25's pushrod length drive net lift. On the other type with pushrod adjuster you set the geometry independent of push rod length and allow that to determine what the length should be.

Seems therefore that the adjuster on the pushrod end is the preferred design, and once again I have bought the wrong part. Since this is the scond set I have imported for the same job I have to live with it.

Good idea to gring the back side of the adjuster, but will see if I can find lash caps here in Thailand, if not then either more expensive importing or I will grind the rocker arms. Perhaps a Jap lash cap will fit and wil be easirer to find here.

Once again, thanks for all the help

[mark tucker]

there is no prefered type. more of a budget or an application type of thing. there is nothing wrong with either system, I have both,my 2028 has the scat rockers with the swivel foot. the raito on that type is pretty close nomatter what cam you run. but with the type that have the ajuster on the pushrod they are more of a variable raito rocker, the more cam lift you have the more lift the rocker can give you, the "foot" (part that contacts the lashcap) is about 15mm long if it contacts the valve at the side close the rocker shaft and "walks across the valve the rocker effectivly gets longer. and tha farther it walks the more raito it gets. with 1 of my cams I had about . 560 witch was 1.42 raito the same rocker with another cam was about .645 witch was about1.55 raito. and that can start breaking parts fast, it is not a bolt on type of rocker like the ones you have, they are more safe for the regular guy not having the knolage or a the tools and a machine shop to do it properly. the foot type 1.25 I have check out at 1.34 on the biger cam witch is exzactly what I wanted for a street motor.but they needed modifying extensively to work. stay with what you have just put on lash caps, and check the push rod tube clearance on all pushrods at 0 lift. you will probably need big diamater tubes.and you can move some of the shims around on the shaft to center the pushrod better in the tube for more clearance. the tip dosent have to be on the center of the valve it can be off .030-.050 with out any problems.(side to side) good luck. and have funn