[BillyGman]

OK guys, pardon me for this novice type comment/question, but since it's related to Rocker arm geometry, well, here goes nuthin'....

This sure is an area I don't know a whole lot about, so reading everyone's posts here has helped to wake me up so to speak in this valve train topic. So after reading this thread, and then looking on through the Crower Rocker arm catalog PDF on thier website, please tell me if I'm getting this right, and if the following statement by Crower is a generalization that's usually ok to go by...

IN a BBC application, (not sure about SBC) according to Crower, the general rule of thumb is when the Overall valve length is .100" longer than factory stock, then a rocker arm with a .050" backset is required in order to get a good narrow contact sweep pattern, (IF the rocker has the standard fulcrum length I guess). Does this usually pan out, or is Crower all wrong on this?

Hopefully I don't drive Scott nuts here with this interjection. I'm simply attempting to do a little research and possibly get a deeper understanding of this geometry topic, (very interesting stuff!).
Now if what Crower claims about .100" longer valves and a .050" backset on the rockers being required holds true, then I'm also wondering how that ties in, or correlates to Scott's AFR Rocker arms. For instance, would his Rocker arms somehow cover all valve lengths on AFR heads, and still provide the best sweep? Or would the .100" or even .150"+ valves being used with the typical 1.625" diameter, and 1.640" dia. springs with their typical taller installed heights, (ie. 2.050" and 2.100" I believe) still require a .050" backset or even a .090" backset on the rocker arms even with the AFR heads? Perhaps nobody can actually provide a definitive answer on that without actually trying them to see what manner of contact pattern sweep is obtained.

Yes, I tend to analize things like this to death until I have a deeper understanding of things.

 

[shovelrick]

That's my understanding, .100 longer valves need the .050 backset rockers to get the best sweep close to the center of the valve tip, ordered a Straub set monday

 

[77 cruiser]

I wouldn't think backset wouldn't affect the width of the pattern, just where it was on the valve.

 

[BillyGman]

That's my understanding, .100 longer valves need the .050 backset rockers to get the best sweep close to the center of the valve tip, ordered a Straub set monday

And which set is that? I'm guessing that it wasn't the ones Scott designed specifically for the AFR heads, because Scott told me that they do NOT have any backset. Instead, he designed them with a different fulcrum length to better suit the AFR rocker geometry required than most other rockers will.

 

[BillyGman]

I wouldn't think backset wouldn't affect the width of the pattern, just where it was on the valve.

I'm not so sure of that. Are you sure? I would think it depends on the actual OAL of the valves being used. Because when the valves being used are longer than standard, then it will change angles of the sweep, or change the throw or the arc of the sweep itself. I'm sure there's a better way to explain that, but that's the best way i can think of at the moment. Ofcourse I can be all wrong on that too.

 

[BillyGman]

Here's another fly in the ointment, or monkey wrench in the works: If it often holds true what Crower states about the longer OAL valve measurement requiring a backset on the rockers, then how come they also claim that only 8 are required for the intake valves only? What about the great OAL of the exhaust valves? Why don't they also require a backset rocker arm? I keep thinking that I'm missing something obvious here.

 

[steelcomp]

I'm not so sure of that. Are you sure? I would think it depends on the actual AOL of the valves being used. Because when the valves being used are longer than standard, then it will change angles of the sweep, or change the throw or the arc of the sweep itself. I'm sure there's a better way to explain that, but that's the best way i can think of at the moment. Of course I can be all wrong on that too.

He is 100% correct. Moving the hole in the trunnion doesn't change the fulcrum length, it just re-locates the rocker and moves the contact pattern. It's more of a bandaid. It also pushes the pushrod closer to the valve cover rail, not that that's an issue on most heads but it can be with some rocker and valve cover combinations. Personally I don't like that the stud hole isn't centered in the trunnion but it doesn't seem to be an issue. It's definitely a compromise and one way to address the issues.
The length of the valves is what's causing this whole issue. We've been over this. The rocker stud and valve angles are converging angles. When you install a longer valve, you have to move the rocker up on the stud accordingly. The longer the valve and the further up you go on the stud, the closer the two become and consequently, the rocker arm needs to be shorter in order to maintain the same correct geometry and keep the sweep pattern centered in the valve. However, when all you are trying to do is center the pattern on the valve tip (as many believe is correct) then just about any length rocker will work. You just keep lowering it on the stud toll you move the pattern back far enough to be centered. Of course, as we see all the time, the pattern is .150" wide and the geometry is off a mile, rockers hit retainers, guides wear out in 1K miles and valve train parts break.
Technically, mathematically, geometrically, there is only one correct rocker configuration for one specific lift, one specific valve height and one specific relationship between valve and rocker stud. The rockers I designed for the AFR heads are designed around .700" lift with the AFR valve train configuration meaning stud location, stud angle and relationship to the valve. The fact that they work on other heads is coincidence. Most BB Chev heads are close enough in design that the very minute differences are inconsequential. If the rocker fits, has proper geometry and the sweep is in the center third of the valve tip, run it.

 

[steelcomp]

OK guys, pardon me for this novice type comment/question, but since it's related to Rocker arm geometry, well, here goes nuthin'....

This sure is an area I don't know a whole lot about, so reading everyone's posts here has helped to wake me up so to speak in this valve train topic. So after reading this thread, and then looking on through the Crower Rocker arm catalog PDF on thier website, please tell me if I'm getting this right, and if the following statement by Crower is a generalization that's usually ok to go by...

IN a BBC application, (not sure about SBC) according to Crower, the general rule of thumb is when the Overall valve length is .100" longer than factory stock, then a rocker arm with a .050" backset is required in order to get a good narrow contact sweep pattern, (IF the rocker has the standard fulcrum length I guess). Does this usually pan out, or is Crower all wrong on this?
This is wrong, or I should say they worded it wrong. The backset rocker does not change the sweep pattern, or the ability to get a good sweep pattern, it simply re-locates it on the valve tip.

Hopefully I don't drive Scott nuts here with this interjection. I'm simply attempting to do a little research and possibly get a deeper understanding of this geometry topic, (very interesting stuff!).
Now if what Crower claims about .100" longer valves and a .050" backset on the rockers being required holds true, then I'm also wondering how that ties in, or correlates to Scott's AFR Rocker arms. For instance, would his Rocker arms somehow cover all valve lengths on AFR heads, and still provide the best sweep? Or would the .100" or even .150"+ valves being used with the typical 1.625" diameter, and 1.640" dia. springs with their typical taller installed heights, (ie. 2.050" and 2.100" I believe) still require a .050" backset or even a .090" backset on the rocker arms even with the AFR heads? Perhaps nobody can actually provide a definitive answer on that without actually trying them to see what manner of contact pattern sweep is obtained.

Yes, I tend to analize things like this to death until I have a deeper understanding of things. Ya think?

Any time you change the geometry of the valve and rocker relationship meaning longer or shorter valves, changing the angle of the rocker stud or valves, or even re-locating either one, you're going to have to change the rocker arm accordingly. The higher you go on the rocker stud in order to accommodate longer valves, the shorter the rocker gets.
AFR installs the same length valves in all their heads. Honestly, they are way too long for most applications but they are setting up for worst case scenario. And before you ask; The reason for longer valves is for taller valve springs with more installed height which allow for more lift. That subject can open a whole entire new discussion and one huge can of worms.

 

[BillyGman]

He is 100% correct. Moving the hole in the trunnion doesn't change the fulcrum length, it just re-locates the rocker and moves the contact pattern. It's more of a bandaid. It also pushes the pushrod closer to the valve cover rail, not that that's an issue on most heads but it can be with some rocker and valve cover combinations. Personally I don't like that the stud hole isn't centered in the trunnion but it doesn't seem to be an issue. It's definitely a compromise and one way to address the issues.
The length of the valves is what's causing this whole issue. We've been over this. The rocker stud and valve angles are converging angles. When you install a longer valve, you have to move the rocker up on the stud accordingly. The longer the valve and the further up you go on the stud, the closer the two become and consequently, the rocker arm needs to be shorter in order to maintain the same correct geometry and keep the sweep pattern centered in the valve. However, when all you are trying to do is center the pattern on the valve tip (as many believe is correct) then just about any length rocker will work. You just keep lowering it on the stud toll you move the pattern back far enough to be centered. Of course, as we see all the time, the pattern is .150" wide and the geometry is off a mile, rockers hit retainers, guides wear out in 1K miles and valve train parts break.
Technically, mathematically, geometrically, there is only one correct rocker configuration for one specific lift, one specific valve height and one specific relationship between valve and rocker stud. The rockers I designed for the AFR heads are designed around .700" lift with the AFR valve train configuration meaning stud location, stud angle and relationship to the valve. The fact that they work on other heads is coincidence. Most BB Chev heads are close enough in design that the very minute differences are inconsequential. If the rocker fits, has proper geometry and the sweep is in the center third of the valve tip, run it.

Thanks again Scott. Yes, now that you mention it, you DID cover that earlier. Especially the converging angles of the rocker stud and the valve angle. My head is spinning with this stuff. I guess I was forgetting about valve angles being 26, 24, 23, 20, 18, 14, 12, and 11 degrees rather than at the angle of the rocker studs. Sorry.

 

[steelcomp]

Here's another fly in the ointment, or monkey wrench in the works: If it often holds true what Crower states about the longer OAL valve measurement requiring a backset on the rockers, then how come they also claim that only 8 are required for the intake valves only? What about the great OAL of the exhaust valves? Why don't they also require a backset rocker arm? I keep thinking that I'm missing something obvious here.

Typical aftermarket BB Chev ex valves are all the same length within .010-.020" and allow for more than enough installed height for 99% of applications -but- they do need a slightly shorter rocker. Crower is trying to cover a lot of bases with one modified rocker. At .050" backset, it's probably too much for the ex valve scenario.
It's the intake valves that vary .05", .100" even .200"-.250" and that .050" backset is simply a "middle ground" compromise. If you want to know the truth, the question I would ask is, "backset from what?" since there is NO standard for roller rocker design in the industry. The OEM's never built a roller tip rocker for any of the factory heads.
Adit to add; in Crower's defense, they would have to offer backsets in .010" increments in order to cover all the different scenarios and even that would be a compromise. LOL...and we're not even addressing pushrod-side geometry.

 

[steelcomp]

Thanks again Scott. Yes, now that you mention it, you DID cover that earlier. Especially the converging angles of the rocker stud and the valve angle. My head is spinning with this stuff. I guess I was forgetting about valve angles being 26, 24, 23, 20, 18, 14, 12, and 11 degrees rather than at the angle of the rocker studs. Sorry.

No worries. It can get very involved and lots to take in. I'm still learning about this stuff every day. Just glad to be able to pass it along as best I can. :thumbsup:

 

[BillyGman]

And before you ask; The reason for longer valves is for taller valve springs with more installed height which allow for more lift. That subject can open a whole entire new discussion and one huge can of worms.

Oh that much I understood, and I do grasp, (believe it or not. ). I just never even considered the taller springs and taller OAL of the valves, creating a different rocker arm requirement on any given cylinder head. Due to your explanation here as well as other peoples' posts, I now know about that. So sometimes the light that goes on seems to bring attention to other areas I was in the dark about. Kinda like that ole expression: "the more I learn, the less I know" Thanks for your patience sir. :bow:

 

[William Hennke]

If you're using my method it's not necessary to run checking springs. In fact, it's not even necessary to turn the engine over other than to make sure the lifter is on the base circle. As long as you get the initial 90* rocker to valve relationship right, the rest is just math.

This is true if you don't actually want to check the actual sweep measurement. If you actually want to check that and have hydraulic lifters you either need checking springs or need to make a hydraulic lifter solid. I still don't know why but if I use the mid lift method on the exhaust with my comp rocker arms the sweep is way wide (.090) and off center by quite a bit. I rechecked this quite a few times and came out wide every time. The AFR rockers fixed the wide pattern and came closer to the center. My opinion is check both ways as verification everything is ok.

 

[MadmanMark]

I have a question Scott might be able to help with. I think he stated that the minimum sweep should be the same between 2 different rockers (both setup with the 90deg 1/2-lift method), and only where it falls on the valve would be different. Seems like there are a lot of different ways to get to a given rocker ratio, so how does the minimum sweep not change? Does this apply to shaft & stud systems?

Good geometry seems to be not as easy as following the 90deg 1/2-lift method, which only optimizes the valve-side of things. It doesn't look at the pushrod-side of things, and I think different rocker arm shapes create different ratio profiles vs valve lift. Seems like there would be 1 optimal rocker configuration for each head/cam lobe/valve combination (and everything else is a compromise).

My frustration comes from playing the pushrod length game on my sbc (AFR210s & older CC rockers). It's just a little over .6 lift, but I couldn't get the pattern under 0.060. The pattern did get a bit wider if I lengthened or shortened the checker.

The good part of "the more you learn, the less you know" is you tend to know more after learning about what you didn't know. The bad part is you probably learn there's a lot more you don't know.

 

[steelcomp]

I have a question Scott might be able to help with. I think he stated that the minimum sweep should be the same between 2 different rockers (both setup with the 90deg 1/2-lift method), and only where it falls on the valve would be different. Seems like there are a lot of different ways to get to a given rocker ratio, so how does the minimum sweep not change? Does this apply to shaft & stud systems?

Good geometry seems to be not as easy as following the 90deg 1/2-lift method, which only optimizes the valve-side of things. It doesn't look at the pushrod-side of things, and I think different rocker arm shapes create different ratio profiles vs valve lift. Seems like there would be 1 optimal rocker configuration for each head/cam lobe/valve combination (and everything else is a compromise).

My frustration comes from playing the pushrod length game on my sbc (AFR210s & older CC rockers). It's just a little over .6 lift, but I couldn't get the pattern under 0.060. The pattern did get a bit wider if I lengthened or shortened the checker.

The good part of "the more you learn, the less you know" is you tend to know more after learning about what you didn't know. The bad part is you probably learn there's a lot more you don't know.

Small block Chev's have short fulcrum lengths. The shorter the fulcrum length, the tighter the radius so the wider the sweep pattern will be, all else being equal. Seems I remember .06" being about as good as you're going to get with most SBC rockers.
You're right about the pushrod side of the rocker needing proper geometry. That's one of the differences between the rockers that I designed and others, even if the valve side fits. The pushrod side is also correct for the AFR heads with .700" lift.
Ratio is ratio. The numerical ratio is mathematical. It's simply the ratio between the distance between the center of the pushrod cup and trunnion, and the center of the roller tip and trunnion. Even if the legs were 90* to eachother, the ratio is still the same. The problem comes in when you start combining linear motion with radial motion. That can change the effective ratio (ratio profile) but at very best, with optimal geometry on both sides of the rocker, you can't get more effective ratio than the numeric ratio. A lot of manufacturers 'over ratio" their rockers to make up for deflection. Proper geometry on the p/r side is the same as on the valve side; there is an imaginary line from the center of the ball of the pushrod, through the center of the trunnion, and that line needs to be 90* to the pushrod at mid-lift. I don't spend a lot of time on that aspect of the rocker since in most cases we can't do a lot about it. Changing that side of the rocker usually means a complete re-design. The valve side is a little more critical and can effect the guide, valve tip, can effect retainer clearance, spring harmonics, all sorts of things. It's also a lot easier to correct.

 

[shovelrick]

BillyGman, I might have worded wrong saying backset rockers? I ordered the rockers that Scott designed (I think they're backset?) I had a chance to change the Brodix studs to ARP 235-7205's yesterday, I cut the exh. studs down to about 1.05 and added an ARP .100 thick parallel washer on exh. studs to give me more height to get more than 6 full turns down on the nuts, BillK thanks for the heat tip and I apologize that I didn't mention thanking you for some other tips you gave me :thumbsup:, I heated for a count of 20 at the tip of the old (new) studs and it made it a lot easier than just breaking the red Loctite loose, it did take the black coating off but oh well, if I would have been thinking I could have used the Comp Ultras & these studs on my 454, another Oh Well :smile2:, here's some pics
edit: if your working from in front of the engine start with the torch at the back studs, I work with torches a lot and still got an Ouch >

 

[shovelrick]

I also left #1 cyl. studs loose in case I do need to put the checker springs on I'll use the Brodix studs so I don't have to worry about messing the arp stud threads up using the spring pry bar tool, hope I can understand how to measure leaving the springs alone, all the int. studs go into ports so I used my finger to wipe any thread sealant that came through, used BillK's way of a little screw driver to get sealant inside the threads and on the stud threads too :thumbsup:
I used a MAP gas torch if anyone was wondering

 

[BillyGman]

BillyGman, I might have worded wrong saying backset rockers? I ordered the rockers that Scott designed (I think they're backset?) I had a chance to change the Brodix studs to ARP 235-7205's yesterday, I cut the exh. studs down to about 1.05 and added an ARP .100 thick parallel washer on exh. studs to give me more height to get more than 6 full turns down on the nuts, BillK thanks for the heat tip and I apologize that I didn't mention thanking you for some other tips you gave me :thumbsup:, I heated for a count of 20 at the tip of the old (new) studs and it made it a lot easier than just breaking the red Loctite loose, it did take the black coating off but oh well, if I would have been thinking I could have used the Comp Ultras & these studs on my 454, another Oh Well :smile2:, here's some pics
edit: if your working from in front of the engine start with the torch at the back studs, I work with torches a lot and still got an Ouch >

No Rick, those rockers don't have any backset to them. That's what Scott told me yesterday. There are other dimensions on them that are different than other rockers instead of having a backset.

I only wish that Summit racing or ARP sold them individually like they do the .050" backset crower SS rockers, because that way I could just buy one from Summit to see what sweep pattern it displays, so I wouldn't have to spring for the whole set before I find out if they will work good with the brodix heads I want to use.

But for me, I already have 16 of the Crower SS rockers, so I'd like to put them to use, however, with the .100+" OAL of the intake valves on the Brodix heads, I'll have to buy a set of 8 of the "Centerline" Crower SS rockers with the .050" backset for the instake valves if I decide to use them, and I'll be able to use 8 out of the 16 standard rockers for the exhaust valves since they'rer shorter than the intakes are. What a tangled web we weave with all this stuff.

 

[shovelrick]

IIRC my sweep was farther away from center on the exh. valves than the int. side

 

[BillyGman]

IIRC my sweep was farther away from center on the exh. valves than the int. side

With what rocker arms? Standard or ones that were backset .050"??