Rocker geometry...my turn - Page 2 - Chevelle Tech
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post #16 of 64 (permalink) Old Mar 20th, 20, 10:19 PM
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Re: Rocker geometry...my turn

I would replace intake and exhaust rockers. Neither of yours are close enough to the center IMO. Definitely be sure you have enough shank/trunion engagement. On my AFR 265 I used 135-7202 on the intakes, and used the exhausts from the 235-7205 kit for Dart heads. Max amount of shank in the trunion with these.
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post #17 of 64 (permalink) Old Mar 21st, 20, 11:11 AM
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Re: Rocker geometry...my turn

Longer pushrods might help that bad geometry.

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post #18 of 64 (permalink) Old Mar 21st, 20, 11:37 AM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by pannetron View Post
Longer pushrods might help that bad geometry.
Proper pushrod length should not be adjusted to center the rocker on the valvestem. Different rockers are required. The midlift method determines pushrod length by using calculations. Do the calculations correctly, and the length that comes out of it is the right one for the application.
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post #19 of 64 (permalink) Old Mar 21st, 20, 2:19 PM
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Re: Rocker geometry...my turn

If having the contact pattern on the valve tip near center is important, I'm curious why AFR didn't simply relocate the rocker studs away from the valves so a variety of commercially available rockers could be used.

Here is an article from 2006 endorsing Miller's mid-lift method for establishing rocker arm geometry.

https://www.hotrod.com/articles/ctrp...rain-geometry/

And here is a quote from about the middle of the article:

"Of course, we don't want to see the roller rocker contact point move any closer than 0.020 inch to the edge of the valve stem, as Smokey has stated, but being off-centered has little negative effect on components such as valve guides and valvetrain harmonics and no effect on performance. It is not a performance enhancement to have the sweep path centered on the valve stem, nor does it necessarily mean that we have the correct VTG if it is centered."

When setting up rocker geometry today I understand we strive to keep the roller contact pattern within the center third of the valve tip. For a 11/32 valve, this means the roller pattern should not be any closer than 0.114" from the edge of the valve. This is nearly six times the distance suggested by Smokey in the 2006 article. I'm sure there is no down side to a centered contact pattern, but is it really necessary or beneficial?
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post #20 of 64 (permalink) Old Mar 21st, 20, 2:29 PM
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Re: Rocker geometry...my turn

If you get the mid-lift setup right, the rocker will be as close to the exhaust-side of the head as it can get at mid-lift. It will move from the intake-side toward the exhaust on the way up, and back toward the intake as it goes past mid-lift to full lift. I've been told minimal sweep is more important than being centered (unless the pattern ends up to close to the valve edge), but I've also seen other theories about where you want the 90deg relationship (usually with big spring pressure/high hp setups).

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post #21 of 64 (permalink) Old Mar 21st, 20, 4:30 PM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by Roadknee View Post
If having the contact pattern on the valve tip near center is important, I'm curious why AFR didn't simply relocate the rocker studs away from the valves so a variety of commercially available rockers could be used.

Here is an article from 2006 endorsing Miller's mid-lift method for establishing rocker arm geometry.

https://www.hotrod.com/articles/ctrp...rain-geometry/

And here is a quote from about the middle of the article:

"Of course, we don't want to see the roller rocker contact point move any closer than 0.020 inch to the edge of the valve stem, as Smokey has stated, but being off-centered has little negative effect on components such as valve guides and valvetrain harmonics and no effect on performance. It is not a performance enhancement to have the sweep path centered on the valve stem, nor does it necessarily mean that we have the correct VTG if it is centered."

When setting up rocker geometry today I understand we strive to keep the roller contact pattern within the center third of the valve tip. For a 11/32 valve, this means the roller pattern should not be any closer than 0.114" from the edge of the valve. This is nearly six times the distance suggested by Smokey in the 2006 article. I'm sure there is no down side to a centered contact pattern, but is it really necessary or beneficial?
Lot of incorrect "assumptions" in that article.
I would like to see the exact article where Smokey said we don't want to see the roller rocker contact point move any closer than 0.020 inch to the edge of the valve stem. I don't believe that to be true...meaning I don't believe he would say that. I think they've either mis-quoted him or taken something out of context. There is no way I would run a roller tip to within .020 of the edge of the valve and I would argue against it with anyone including Smokey.
Whether it's really necessary or beneficial...that's completely up to the individual. None of this is mandatory in life.

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post #22 of 64 (permalink) Old Mar 21st, 20, 4:32 PM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by pannetron View Post
Longer pushrods might help that bad geometry.
Rocker geometry has nothing to do with pushrod length. Pushrod length is a result of rocker geometry, good or bad.
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post #23 of 64 (permalink) Old Mar 22nd, 20, 8:04 AM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by MarkP View Post
No Vince, .904 diameter 5470 Morel hydraulics, which are about.100 taller than the ones I had in there. Was using Morel hydraulic 4603 lifter before they got gouged up. The checking springs will collapse the lifters, so doing sweeps for length isn't really reliable. That's why measuring pushrods using Scott's 90 degree method does make sense to me.

I rolled the engine over until I was at half lift on the valve. The lifter collapsing doesn't matter at this point because I just wanted to see where the lifter roller tip was on the valve at half lift. The rocker is at 90 degrees at half lift.



Bill, these are Scorpion 1014 1.7 BBC rockers. The original set of silver 1014 rockers had grit in them from the two engine failures that I had, so I sent them back to Scorpion and they replaced them for free.

The Scorpion person that I talked to said that they changed the geometry somewhat from the older silver ones that I did have. My poly lock set screw sits about .200" in the in the hole, so I was concerned. The rockers are sitting on the threads of the stud, so I got the shorter adjustment threaded ARP 235-7205 to replace the 235-7202 that are on it now.

Mike Lewis had a procedure to check the sweep by hand using the piston as a stop for the valve. I have to go look that up before I order push rods. I have to get the roller tip where it needs to be before I order push rods.

Gotcha. My geometry looked exactly like yours with my 305's and Crane rockers. I called it a day and shortened the pushrod a hair vs buying new rockers. I think the Cranes may give a better pattern vs the Scorpion though.

PS - I used this to lock the valve down to midlift position and then find the 90* rocker to valve relationship. Although the piston method could work also.


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post #24 of 64 (permalink) Old Mar 22nd, 20, 4:41 PM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by steelcomp View Post
Lot of incorrect "assumptions" in that article.
I would like to see the exact article where Smokey said we don't want to see the roller rocker contact point move any closer than 0.020 inch to the edge of the valve stem. I don't believe that to be true...meaning I don't believe he would say that. I think they've either mis-quoted him or taken something out of context. There is no way I would run a roller tip to within .020 of the edge of the valve and I would argue against it with anyone including Smokey.
Whether it's really necessary or beneficial...that's completely up to the individual. None of this is mandatory in life.
Smokey discussed the 0.020" distance in his Power Secrets book (page 88). I'm not aware of it being referenced in another article. He goes on to discuss the importance of the rocker tip not rolling off the tip of the valve. I've seen enough Spintron videos with the valve bouncing and bending at speed to conclude that 0.020" is too close for comfort. I understand just because 0.020" is written in a book doesn't mean it shouldn't be questioned. A similar example is Vizard instructing the reader to select pushrod length to center the roller contact pattern on the valvetip in his latest BBC book. And it was published in 2015.

I do think anyone in the market for BBC full roller rockers should purchase the AFR rockers you designed because (1) there is no downside to having the contact pattern centered on the valve tip, (2) pushrod side geometry is also correct, and (3) they are competitively priced. I also think a good existing set of rockers can be used even if the contact pattern is noticeably off center with no downside, provided proper geometry is achieved.

I'd be interested in learning more about your thoughts on the lot of incorrect assumptions in the article I referenced when you get a chance.
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post #25 of 64 (permalink) Old Mar 25th, 20, 4:19 AM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by Roadknee View Post
If having the contact pattern on the valve tip near center is important, I'm curious why AFR didn't simply relocate the rocker studs away from the valves so a variety of commercially available rockers could be used.
I'm still very much a student and learning on this whole valve train geometry topic, but I'm going to attempt to give you an answer to your question based on the understanding that I've gained so far, (if I'm wrong then I'm sure that someone will correct me): I'm not so sure there can actually be an ideal rocker arm stud hole location that would allow most any standard roller rockerarm to be used. The reason for that is due to the fact that the rocker arm stud angle converges with the angle of the valve, so the longer the valve stem is, and the taller the installed height of the valve spring is, the closer it brings the rockerarm to the valve stem.

In a recent conversation I had with engine builder Mike Lewis, he mentioned to me that there isn't really any such thing as standard nor long valves anymore, due to the fact that there are so many valve length options these days. If I may add to his thought on that, I'd also say that there is also a plethora of cam lobe options, offering the end user from .450" total lift at the valves, to close to .900" lift, (with the majority being from .500" to .775" lift). The point being that there are so many possible valve train combinations and so many variables, that it's probably impossible for any head manufacture to locate the rocker stud holes in a place that would make it possible for most rockerarms to be used by most of their customers. The more valve length you use, and the taller you go with the installed spring height, (in order to avoid coil bind when using high lift camshafts) the higher your rocker arm ends up resting on the rocker stud, and in turn the closer it gets to the valve stem.

Remember, the angles of the rocker studs and of the valves converge with eachother. The two angles are slanted towards eachother. Therefore, there is really no way that a cylinder head manufacture can re-locate the rocker stud holes to a place that would serve as a cure-all for any possible combination of cam lift, valve length, and valve spring installed height.

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post #26 of 64 (permalink) Old Mar 25th, 20, 6:38 AM
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Re: Rocker geometry...my turn

doesn't seem that complex to me, if the BBC head comes with a valve and spring setup for .600" lift they need to tilt the rocker stud to fit a 1.65" rocker correctly, I can't visualize what problem that change would generate, they all need specific length pushrods and stud girdles anyway, actually moving the stud say .050" might cause some interference issue somewhere but changing the angle seems doable to me
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post #27 of 64 (permalink) Old Mar 25th, 20, 7:40 AM
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Re: Rocker geometry...my turn

This is how mine came out with Straub INT. rockers on all valves, I'm very happy and also like these Trend perf. PRs I still need to put #1 springs back on and adjust them, this is with Howards (Gatorman) max effort lifters
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post #28 of 64 (permalink) Old Mar 25th, 20, 7:59 AM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by steelcomp View Post
Rocker geometry has nothing to do with pushrod length. Pushrod length is a result of rocker geometry, good or bad.
Found another fresh video by so called experts.

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post #29 of 64 (permalink) Old Mar 25th, 20, 10:25 AM
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Re: Rocker geometry...my turn

Quote:
Originally Posted by pbcbob View Post
doesn't seem that complex to me, if the BBC head comes with a valve and spring setup for .600" lift they need to tilt the rocker stud to fit a 1.65" rocker correctly, I can't visualize what problem that change would generate, they all need specific length pushrods and stud girdles anyway, actually moving the stud say .050" might cause some interference issue somewhere but changing the angle seems doable to me
The angle of the stud has to bisect the angle between the valve and pushrod otherwise the stud would be in a bending scenario.
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post #30 of 64 (permalink) Old Mar 25th, 20, 10:31 AM
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Re: Rocker geometry...my turn

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Perfect example of what NOT to do. This is the exact kind of nonsense and misinformation that is out there and can ruin a nice new set of heads in no time.
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