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Discussion Starter · #1 · (Edited)
I’ve been attempting to correcting my VTG towards the thought of Scott from staubs Technology using the 90deg relationship between the axi of the valve stem’s relationship with the line drawer from the centre of the trunion to the centre of the roller tip amd have come up with this as a comparitive sweep.
617255


in conclusion , opted for the more narrow sweep of 1.25mm compared to the 3.1mm sweep, albeit more outboard from centre…..
now my rocker lock nut is only secured by means of 3.25=turns as opposed to 6.5 turns before.
I feel I need longer rocker studs.
does someone know where the length of a rocker stud is measured, just so I know what length to order, thAnks

duke

ive gone from 7.900” (what world heads said that I needed , being 100 thou longer than the stock 7.817” or whatever…to 8.200” to get it right.
just saying this for people who don’t realise that pushrod length is the last decision to be be made in engine building questions
 

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When you are using roller rocker arms, the width of the sweep really isn't worth worrying about. You are better with the wider sweep because its centered over the stem and pushing less against the guide causing premature wear. There are some people who "excess" toward making the rocker push down at an odd angle to get the sweep narrower. I believe they lose some of their lift by trying to trick the geometry. At the least they induce additional wear and pressure. A rocker arm is designed to work a certain way and while some people always look for "additional tricks" to gain HP, often there is no gain and other issues arise. My recommendation is to go with the wider sweeping motion that the rocker is designed for. You are right to make the pushrod length something that gets decided late in the assembly process, and to actually measure it. Many people don't realize that decking a block and/or resurfacing a head.......and maybe even a different type of head gasket can have a major effect when the rockers/lifters are installed. One more thing......in you picture with the narrow band, it looks like it not smooth and it also looks like its not "square" with the axis of the valve.

Again.......You say you have made a major change in pushrod length and now the rocker studs are too short. I think that might indicate that you "might" be going in the wrong direction. Don't take this the wrong way please. I'm trying to be helpful by giving an honest opinion (I been wrong before), so I'm telling you what I honestly think. If you make your studs longer, you may need to use a stud girdle to prevent flex. There was a knowledgeable guy on another site who chased a vibration in his hot rod. Finally turned out to be the studs flexing and a stud girdle cured the problem. Another consideration is valve cover clearance if you raise things too far. I'd like to see a side view of the geometry you are getting when you are moched up the way you are trying to do it. Good Luck!
 

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Narrowest sweep gives max lift and both of these occur when set up using pushrods determined by the mid-lift method.

If your cam is moderate lift and studs are normal length, then I would think the stud bosses on the heads are machined too low, or your valves are somehow too long, or maybe there is something going on with the rocker or rocker installation like flipping the trunion upside down if it is offset somehow.

What rockers are you using? Is this the same engine or heads you was posting about back in 2017?
 

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I’d go with the wider sweep that is centered. The more offset from center the sweep is the more force angularity is being imposed on the valve stem. This increases guide wear both in the speed with which it happens and the severity . Quickly you will have the resultant problems of the valve not seating without having to roll or orbit on the seat first and the wear on the guides will sock the stem in its seal allowing oil in excess an mounts down the guide. The stiffer the valve springs and the higher the RPMs the faster this happens.

In regard to rolling or orbiting on the seat, it is important to consider the valve doesn’t simply go up and down rather the compression and release of the spring as it cycles between closed to open to closed again imparts a rotation that carries the spring, retainer, locks and valve in a circular motion. As the guide wears the valve will touch down on one side first to where the seats are sliding against each other forcing this rolling motion onto the stem, so it just becomes this problem on problem.

Now while the narrowest sweep supplies the best information transfer from the lobe in your case of being off center by quite a bit imparts maximum wear. So without correction your stuck with a choice between maximum performance with maximum wear or slightly moderated peak performance with minimized wear. A competitive racer would choose maximized performance with maximized wear because to keep the engine on that edge it is going to see tear downs based on wear that degrades performance, whether that means between heats, between races, monthly or seasonally just depends on what analysis finds. For the average guy with a street rod that isn’t looking for frequent inspections and repairs then the low wear solution is the better answer.

Bogie
 

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Some thoughts.....Sweeps are all about where the most movement happens in relation to the lift curve. It's all in the math

On the wider sweep pattern, if that pattern STARTS on one side, when the spring load is LOW and migrates across the tip to full lift at center when the spring load is highest, that will be okay. So okay in fact, its the general conses with Jesel and [email protected] many others do it this way and they have more testing than any of us.

IF the wide sweep starts in the middle at low springs loads and migrates to the edge at high spring loads than it'll wear out guides faster BUT also gives a a tad more lift in the curve.

IF this is an engine that you don't want to refreshen often, stick with the narrow sweep pattern as it's going to favor the guides for valve timing.

In all honesty, you have already made several compromises anyway, as all engine are, the narrow pattern isn't close enough to the edge to worry about. I'd go there and not worry about getting longer studs and all that. you would end up spending a lot of money and netting very little to nothing by doing so.
 

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I am not sure what I am seeing. What length pushrods did you use to get each pattern? I assume each pattern had a different length push rod. You went from 7.900 to 8.200. That is a lot of difference. How did you arrive at the 8.200 length? Did you try all the rod lengths in between? If it was me I would install checking springs and an adjustable push rod. The 90 degree method works very well if done right (I also watched the video) but you should still check the pattern. In the video checking springs were used I believe. If the lifters are hydraulic this should not be done with the installed valve springs. Installing checking springs is very easy and makes this task easier and you can get lengths in-between the stand lengths for fine tuning and then pick the closest standard length. The checking springs do not collapse the lifters so this variable is removed. It appears to me from looking at the patterns something is wrong.

I would not settle with either pattern and would do as I suggested above. The patterns are too different.

Also be carful you do not go past 90 degrees at half valve lift. This is easy to do and with too long a push rod. Start with the 90 degree method and then adjust rod length in small increments until you get the best pattern. I am assuming you got small pattern with the 7.900 push rod using the 90 degree method and the other pattern with 8.200 rods. IF this is true you need a shorter push rod not longer and you went past 90 degrees at mid lift.
More information would be a big help.
 

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I just thought maybe you did it backwards from what I said. Did you get the small pattern with the longer pushrod and the wider pattern with the shorter rod? If you did you are correct. Maybe something in between the two would work. We need to know which pattern came from which length pushrod.
 

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Some of you guys all worried about the sweep pattern being off center and it leading to guide wear are missing the fact that with either Jesel geometry or mid-lift geometry both roller tips start at an inboard location, move out to the furthest point at either mid lift or the 2/3? lift(whatever the Jesel figure is I dont know?) and then moves back toward the start point at full lift......

With a stud mount rocker If you start with the pushrod cup so low that the roller tip pattern starts inboard, moves outward at 1/2 lift and moves even farther outward at full lift while leaving a wide but perfectly centered pattern, it will eat the guides right out of it.....the entire travel of the roller tip it is pushing outboard all the way to full lift, side loading the valve in the guide.

It's not what location on the tip you push down at, it is how much you are moving sideways at the same time that causes the side loading to the guide

Either mid-lift or Jesel geometry when applied current stud mounted rocker arms will typically jump pushrod length at least .200" compared to old school thinking, and often more like .300-.400"

Duke,
What your looking for is "effective length" on the stud, that's the distance from the bottom of the hex on the stud to the tip of the rocker arm section.
They will also give length for the end screwed into the head and a length for the section of threads on the rocker end of the stud.
 

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Discussion Starter · #9 ·
Holy ‘roller tip footprint’ Batman! …now I’m more confused than ever.

The big fat wide sweep (centred, or real close) is what I have atm, using the 7.900” pushrods, which are .100” longer than standard. I used that length because that’s the length that World Products said in their pamphlet that needed to be used with the Sportsman II Heads that I am running.

These are in the engine currently and it has done around 4,000 miles.

At that point i was not privy to the teachings of Scott Foxwell from Straubtech Technologies.

Using the 7.900” pushrods, the sweep is centred and wide.

awill923… yes, I mocked the thing using light checker springs during the set up. I calculated the head gasket thickness to achieve proper quench (tight). I forget now the actual figure for quench but .028” comes to mind but I may be wrong, can’t remember but it was on the tight side it’s been a long time. And got pistons with the right pin height, not rebuilders, blank, and had them fly cut for valve relief custom, to get my SCR up to 11.3:1 in order to get the DCR where it needed to be. Cylinder pressures are 200 psi from memory. I did have to undercut the rockers on some cylinders where they interfered with a head bolt here and there.

(2001Blazer4x4… no, different build, that was a whole other nightmare working with Pro-Comp rubbish from chYna..)

Since being schooled by Scott (from Straubtech) I decided it be best that I recheck things and upon applying the mid-lift approach the geometry was ‘way’ off. The angle of the rocker to the centreline of the valve stem was low on the pushrod side by a ‘lot’.
When I squared a line extrapolated from the face of the spring retainer and checked it’s parallel with the axis of the rocker arm (centre to centre, roller tip centre to trunnion centre), the pushrod side was lower by a lot 6.75mm (sorry, we use metric here in AUS, much simpler, no offence 😆)
Soo…..I (using an adjustable pushrod) (engine is complete and going) …lengthened the adjustable pushrod to a length where I am at 90 deg rocker (see Scott’s video) in relation to valve stem, and 8.200” length pushrod is the result of that exercise.

If this method is wrong, someone please tell me.

Old Bogie, sorry Bogies Annex, you say you would go with the wider sweep centred. Ericnova 72, you seem to concur with Scott’s theory/method and not be overly concerned if it not centred, so long as it’s not more than one third off centre, consistent with Scott’s theory.

I respect to both of your views, {and for me it’s way easier to simply leave it as it is with the wide 3.25mm or whatever (centred sweep) and not have to now get longer rocker studs to accommodate the longer pushrods (which I have already purchased)} I just don’t want to flog out the guides.

I can go either way or somewhere in between. I have parts now to do either.


This is not a daily driver but it’s not a competition rig either. It’s my fun/happy place car and I just don’t want to be yanking the heads for servicing anytime soon.
What i am trying to achieve is ‘minimal valve guide wear’.

Also, while I was determining mid lift on the valve, I measured (using a fixed dial gauge) that the valve lift was .510” and not .525” as quoted on the cam card. That finding was measured using the 7.900” pushrods that are currently in the engine. Given other research that I have done, that lower lift seemed to be consistent with the fact that the pushrod currently in the engine is to short also. And ‘no, that cam is not flat’ been the done that.

Phew, that was a mouth full, if any more details are needed please ask.

I don’t discount anyone’s opinion (Curtis, Lemongrass , or anyone) I’m simply searching for the truth.

Thank you all so much for your help,

Duke
 

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Discussion Starter · #10 ·
I just thought maybe you did it backwards from what I said. Did you get the small pattern with the longer pushrod and the wider pattern with the shorter rod? If you did you are correct. Maybe something in between the two would work. We need to know which pattern came from which length pushrod.
The fatter, cantered pattern came using the 7.900” pushrod and the narrower off centre pattern comes using the 8.200” pushrod

Duke
 

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Discussion Starter · #12 ·
Some of you guys all worried about the sweep pattern being off center and it leading to guide wear are missing the fact that with either Jesel geometry or mid-lift geometry both roller tips start at an inboard location, move out to the furthest point at either mid lift or the 2/3? lift(whatever the Jesel figure is I dont know?) and then moves back toward the start point at full lift......

With a stud mount rocker If you start with the pushrod cup so low that the roller tip pattern starts inboard, moves outward at 1/2 lift and moves even farther outward at full lift while leaving a wide but perfectly centered pattern, it will eat the guides right out of it.....the entire travel of the roller tip it is pushing outboard all the way to full lift, side loading the valve in the guide.

It's not what location on the tip you push down at, it is how much you are moving sideways at the same time that causes the side loading to the guide

Either mid-lift or Jesel geometry when applied current stud mounted rocker arms will typically jump pushrod length at least .200" compared to old school thinking, and often more like .300-.400"

Duke,
What your looking for is "effective length" on the stud, that's the distance from the bottom of the hex on the stud to the tip of the rocker arm section.
They will also give length for the end screwed into the head and a length for the section of threads on the rocker end of the stud.
…It jumped mine like +.400” to get the mid lift method to equate, but it’s now off centre as per the picture. The smaller sweep that I measured best I could, 1.25mm happens using a 8.200” length pushrod. This set up gives me near to exactly 90deg relationship rocker centre line to valve centre line

Duke
 

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Discussion Starter · #13 ·
Some of you guys all worried about the sweep pattern being off center and it leading to guide wear are missing the fact that with either Jesel geometry or mid-lift geometry both roller tips start at an inboard location, move out to the furthest point at either mid lift or the 2/3? lift(whatever the Jesel figure is I dont know?) and then moves back toward the start point at full lift......

With a stud mount rocker If you start with the pushrod cup so low that the roller tip pattern starts inboard, moves outward at 1/2 lift and moves even farther outward at full lift while leaving a wide but perfectly centered pattern, it will eat the guides right out of it.....the entire travel of the roller tip it is pushing outboard all the way to full lift, side loading the valve in the guide.

It's not what location on the tip you push down at, it is how much you are moving sideways at the same time that causes the side loading to the guide

Either mid-lift or Jesel geometry when applied current stud mounted rocker arms will typically jump pushrod length at least .200" compared to old school thinking, and often more like .300-.400"

Duke,
What your looking for is "effective length" on the stud, that's the distance from the bottom of the hex on the stud to the tip of the rocker arm section.
They will also give length for the end screwed into the head and a length for the section of threads on the rocker end of the stud.
I’m not familiar with the ‘ Jesel’ method, heck !
surley there is a correct way to do this!
I deal with intricaciies on a daily basis, not thousands in this case, but close tolerances never the less (relative)
how is this done using basic known, tried principles?
surely we come a ways since the fifties, to get the practice correct, is it not so?
shake my head!
Duke
 

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The fatter, cantered pattern came using the 7.900” pushrod and the narrower off centre pattern comes using the 8.200” pushrod
It appears you did it correctly. As for which is the best pattern you should listen to the others as this is beyond my knowledge. With roller rocker arms the tip rolls so how much side force is applied to the valve I do not know. Maybe there is a compromise in-between the two. I would think the rolling of the rocker over the valve causing a wide pattern would be worse than a small pattern off center. Just my opinion.
 

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Discussion Starter · #15 · (Edited)
It appears you did it correctly. As for which is the best pattern you should listen to the others as this is beyond my knowledge. With roller rocker arms the tip rolls so how much side force is applied to the valve I do not know. Maybe there is a compromise in-between the two. I would think the rolling of the rocker over the valve causing a wide pattern would be worse than a small pattern off center. Just my opinion.
Me too from my research. I’m awaiting replies. I think a wider footprint incurs more side wear to the valve guide to stem, due to the wide span of downward load albeit at varying pressures during its travel, Scott’s approach, but Bogies comments throw a whole other perspective on the possibilities/dynamics. I listen to all and try to eventuate to a sensible decision .
this all should not be so complicated….I’m leaning towards the 90 deg @ mid lift , narrow footprint approach , albeit off centre to the valve stem axis resulting in less side load pressures on the guide, due to the simpler action of strai up/straight down movement of the valve, rather that the push the valve tip ‘out and down at the same time, then let it up as well at the same time as the roller sweeps and pushes down and up tha valve, that makes more sense to me in my analytical mind as I feel that there would be less lateral forces and wear.
where as the very narrow/ less sweeping action of the rocker tip would incur more minimal side load…..do I have this arse up?

Duke
 

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Discussion Starter · #16 ·
Me too from my research. I’m awaiting replies. I think a wider footprint incurs more side wear to the valve guide to stem, due to the wide span of downward load albeit at varying pressures during its travel, Scott’s approach, but Bogies comments throw a whole other perspective on the possibilities/dynamics. I listen to all and try to eventuate to a sensible decision .
this all should not be so complicated….I’m leaning towards the 90 deg @ mid lift , narrow footprint approach , albeit off centre to the valve stem axis resulting in less side load pressures on the guide, due to the simpler action of strai up/straight down movement of the valve, rather that the push the valve tip ‘out and down at the same time, then let it up as well at the same time as the roller sweeps and pushes down and up tha valve, that makes more sense to me in my analytical mind as I feel that there would be less lateral forces and wear.
where as the very narrow/ less sweeping action of the rocker tip would incur more minimal side load…..or do I have this wrong?

Duke
 

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Again, when you play the game of trying to make a rocker arm work "more efficiently" by placing it in a mechanical relationship thats abnormal, you create OTHER complications. The resultant gain in power (if any) isn't worth the added strain placed on the parts...... Virtually all the experts show centering for the location of the rockers roller. Think about how many times you have tried to pry something in order to move it or lift it. Even though the length of your pry bar didn't change, WHERE you applied the force to the attending part made a big difference. When you start cocking rocker arms at odd angles but want to move the same distance, you put more stresses on all the involved parts. Take the time to watch these two videos and they should answer all your questions.


 

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Reread my post and Erics post. They are telling you that "proper" is a subjective term and very dependent on the application. That is why you are getting conflicting and confusing info from the internet.

There is the easy way that most large companies push for because it's mostly idiot proof, then there is the way that most bench racers talk about, then there is the way professionals do based on the application.

If long guide wear is your goal, aim for the minimum sweep method, about .060 wide or less, centered somewhere in the middle 2/3 of the stem. The Mid lift theory is the easiest and accurate way of getting there without taking guesses and buying a bunch of push rods.

Bench racers tend to talk in absolutes, fun for the beer table but not always very applicable because of machining tolerances of the parts themselves.

Professionals tend to start with deciding between more lift, more guide wear, and the applications as well as budget constraints. As an example, at $60k 440ci wide bore intended to run at 8500rpm for days and come back after 20 nights for a $10k refreshes can tolerate some guide wear as long as it's making power and staying together for that 20 nights.
They also might have several sets of rockers and push rods laying around for testing and fitment as well as a much better stand and valve angle relationships to start with. The 23 degree SBC works great for a stock stuff but has it's limits and ya kinda have to work with what ya got cause moving the valves and studs isn't very easy. Then there is everything in between the two extremes here.

Ill make this easy for you, aim for the minumum sweep method, about .060 wide or less, centered somewhere in centered 2/3rds of the stem and go worry about something else because getting nit picky for your project is just going to anooy you, confuse you, and you'll end up frustrated and feeling like maybe you should have better choices.
 

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I agree with johnsongrass. You are dealing with fixed geometry. The angle of the rocker arm stud and the valve are not parallel. The valve slants back to the rocker arm stud. As the valve tip position changes for whatever reason, longer valve than stock or valve sunk into the head to far, the distance at 90 degrees may not put you in the center of the valve. Find a compromise that puts you in the 2/3 area and keeps the sweep in the .050 - .060 range and be done with it!
 

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Can the roller on the rocker arm impart a significant radial force to the valve tip as the rocker operates? Would hardened lash caps limit that force at all?

I have seen engine with geometry that should be very good blow out the guides in 5,000 miles, while engine with haphazard geometry seemingly last forever. Maybe the guide material is the problem.
 
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