Re: Rocker arm geometry on a 440
[Re: JohnRR]
#1414027
04/03/13 03:56 PM
04/03/13 03:56 PM
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Joined: Jan 2003
Posts: 31,056 Oregon
AndyF
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Quote:
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I'm not sure that shimming will make it worse, take it to the extreme i.e. if you shimmed it an inch, the arc of the tip would be passing the valve on the inside, or is my reasoning wrong??
Joe
that was my thought , but that was ASSuMEing the rocker shaft holdown pedestals were parallel to the valve stems , they angle toward the valves it seems, I don't have a head handy to confirm this.
15 degree valve angle which really messes up the geometry. As you raise the rocker shaft it gets closer to the valves.
I have a CAD drawing that details all of this out. It is kind of interesting to watch what happens with rocker arm scrub when you change the location of the shaft. Checking the scrub distance with a dial indicator is a good way to verify what is going on. Then you have an actual number that you can work with.
Sometimes the rocker shaft has to be moved a fair amount before the scrub distance is brought back in line. Ideally you want the minimum scrub distance as well as a centered pattern. That is tough to do with some of the rocker arms that are on the market.
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Re: Rocker arm geometry on a 440
[Re: AndyF]
#1414028
04/03/13 04:55 PM
04/03/13 04:55 PM
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Joined: Sep 2006
Posts: 685 SW Ohio
AAR-B4
mopar
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mopar
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SW Ohio
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What will you gain by centering the roller contact? You have added the roller, that will greatly reduce the side-load on the valve stem and save the guide. Put it together, race it and have fun.
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Re: Rocker arm geometry on a 440
[Re: AAR-B4]
#1414030
04/03/13 05:58 PM
04/03/13 05:58 PM
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Joined: Oct 2005
Posts: 8,899 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,899
Ontario, Canada
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Quote:
Quote:
I'm not sure that shimming will make it worse, take it to the extreme i.e. if you shimmed it an inch, the arc of the tip would be passing the valve on the inside, or is my reasoning wrong??
Joe
Well that's just crazy logic. Theoretically if you lowered the shafts and inch it would accomplish the same thing! Think realistically and shimming the shafts does not solve the problem.
The solution is to run them as they are and don't worry about it. You have quality parts and a mild cam.
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Re: Rocker arm geometry on a 440
[Re: moparguy]
#1414032
04/03/13 06:36 PM
04/03/13 06:36 PM
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Joined: Oct 2007
Posts: 4,209 New York
polyspheric
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If the valve-side lever length is wrong (more common than we would like) re-arranging the heights to cure it will make the geo worse. The "scrub path" length and behavior on the stem is far more important.
The best path is the shortest, and begins at 0% lift (valve closed) with the roller tip closest to the rocker shaft, and to the stem’s near edge (not the center).
As the valve opens, the roller walks toward the stem center, is centered in its own path (which may not be the stem tip’s center) at 25% lift.
It reaches its farthest point away from the rocker shaft at 50% lift, then reverses direction.
The roller walks back, reaching its path center again at 75% lift.
Full lift is, again, at the closest point to the shaft and its original resting place.
Boffin Emeritus
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Re: Rocker arm geometry on a 440
[Re: polyspheric]
#1414034
04/03/13 11:35 PM
04/03/13 11:35 PM
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Joined: Oct 2005
Posts: 8,899 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,899
Ontario, Canada
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Quote:
If the valve-side lever length is wrong (more common than we would like) re-arranging the heights to cure it will make the geo worse. The "scrub path" length and behavior on the stem is far more important.
The best path is the shortest, and begins at 0% lift (valve closed) with the roller tip closest to the rocker shaft, and to the stem’s near edge (not the center).
As the valve opens, the roller walks toward the stem center, is centered in its own path (which may not be the stem tip’s center) at 25% lift.
It reaches its farthest point away from the rocker shaft at 50% lift, then reverses direction.
The roller walks back, reaching its path center again at 75% lift.
Full lift is, again, at the closest point to the shaft and its original resting place.
But this will only happen on a specific lift. For example all the ideal roller/tip positions may occur on a .600 lift cam but on an cam with more or less lift these points will be off. Ideally you need to match the cam to the rocker or vice versa. I hate to say it but there are advantages to the "stud" system.
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Re: Rocker arm geometry on a 440
[Re: Stanton]
#1414036
04/04/13 01:33 PM
04/04/13 01:33 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
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To add another factor, where the arm begins and ends its path also has an effect on the actual valve opening curve. It is possible to have the valve come off the seat faster with the same ratio by chainging the heightt of the rocker shaft and rocker cup with respect to the top of the closed valve's stem. There are some interesting Websites devoted to this issue. R.
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Re: Rocker arm geometry on a 440
[Re: CSK]
#1414038
04/04/13 04:03 PM
04/04/13 04:03 PM
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Joined: Jan 2003
Posts: 75,074 U.S.S.A.
JohnRR
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Yes, that is also a very good point. The factory rocker arm geometry is designed for valve lift of roughly 0.400 inches. Which is exactly what you would expect since that is what the lift was when those heads were designed in the late 50's.
To keep the geometry correct, you have to lower the rocker shaft into the head 50% of the additional lift. So if you go from 0.400 lift to 0.600 lift, the rocker shaft should be lowered 0.100.
The only reason to use shims if if you are running less lift than the original design of 0.400. Most people don't do that.
The problem is that if you lower the rocker shaft it moves away from the valve so then you need a longer rocker arm. Best fix for stock heads is to mill off the pads and use offset blocks like the factory designed for the W2. Then you can lower the shaft and move it into position. But then you need to modify the pushrod holes and all of that jazz.
I think the serious class racers used to do all of this stuff years ago. Not sure if anyone still does it anymore. They probably just send their heads to Jesel for modification if Jesel valve gear is allowed in the class rules.
I wrote up all of this information years ago in a magazine article and then covered it again in my big block book. Not sure why I'm bothering to type it in again here.
so why not just use a longer valve ?
One could , finding the right length will be the fun part , that's why a lash cap would be one alternative.
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Re: Rocker arm geometry on a 440
[Re: AndyF]
#1414040
04/06/13 11:21 PM
04/06/13 11:21 PM
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Joined: Nov 2005
Posts: 808 mckinney texas
shoebox
super stock
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super stock
Joined: Nov 2005
Posts: 808
mckinney texas
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I wrote up all of this information years ago in a magazine article and then covered it again in my big block book. Not sure why I'm bothering to type it in again here. Why would you say it all again? Don't get involved with lil guy questions Let him buy your book and figure it out You can stay " up here" And we'll be "down here" helping each other because were mopar Brothers
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Re: Rocker arm geometry on a 440
[Re: shoebox]
#1414041
04/07/13 10:25 AM
04/07/13 10:25 AM
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Joined: Jul 2005
Posts: 1,301 Penna
70satelliteguy
pro stock
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pro stock
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Penna
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"Why would you say it all again? Don't get involved with lil guy questions Let him buy your book and figure it out You can stay " up here" " " And we'll be "down here" helping each other because were mopar" You got something against Andy trying to help someone out!
Last edited by 70satelliteguy; 04/07/13 10:30 AM.
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Re: Rocker arm geometry on a 440
[Re: gregsdart]
#1414043
04/07/13 03:49 PM
04/07/13 03:49 PM
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Joined: Jan 2004
Posts: 27,347 Today? Who Knows?
1_WILD_RT
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I've saved a few pictures from threads about rocker geometry in the past... First the rocker arm length that Andy mentioned... It would be nice it the rocker brands were mentioned ....
"The Armies of our ancestors were lucky, in that they were not trailed by a second army of pencil pushers."
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Re: Rocker arm geometry on a 440
[Re: 1_WILD_RT]
#1414044
04/07/13 03:55 PM
04/07/13 03:55 PM
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Joined: Jan 2004
Posts: 27,347 Today? Who Knows?
1_WILD_RT
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And second the hold down bolt vs valve stem angle..
"The Armies of our ancestors were lucky, in that they were not trailed by a second army of pencil pushers."
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Re: Rocker arm geometry on a 440
[Re: 1_WILD_RT]
#1414045
04/08/13 11:25 AM
04/08/13 11:25 AM
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Joined: Jan 2003
Posts: 75,074 U.S.S.A.
JohnRR
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Quote:
And second the hold down bolt vs valve stem angle..
Good picture , now I see why going up with the shaft will make it worse. Looks like I may have to shelve the HS rockers and go for something else on my 906's
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Re: Rocker arm geometry on a 440
[Re: 1_WILD_RT]
#1414046
04/08/13 11:34 AM
04/08/13 11:34 AM
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Joined: Jan 2003
Posts: 6,988 Warren, MI
Jerry
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Warren, MI
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Quote:
I've saved a few pictures from threads about rocker geometry in the past... First the rocker arm length that Andy mentioned... It would be nice it the rocker brands were mentioned ....
in the pic it looks like the don't know; crane roller rocker; don't know; harland sharp; crane ductile iron ; comp stainless steel rocker
this is my guess at looking at the various pics. hopefully this is a little help full.
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