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1932bantam 10-10-2011 08:41 AM

mid lift rockers
 
Has anybody had any experience using the mid lift pvs rockerarms? Also any opinions on the theory jim miller used developing this system. I just got a new set given to me . you can google jim miller rocker arms and read the history of midlift pretty interesting. looking for someone a little brighter than me for opinions. thanks

oldbogie 10-10-2011 02:47 PM

Quote:

Originally Posted by 1932bantam
Has anybody had any experience using the mid lift pvs rockerarms? Also any opinions on the theory jim miller used developing this system. I just got a new set given to me . you can google jim miller rocker arms and read the history of midlift pretty interesting. looking for someone a little brighter than me for opinions. thanks

I've run these on several builds over the years. They are are a good as any of the "real" high performance roller rockers as any quality rocker on the market. There was a spate of manufacturing errors made several years ago, these were said to be reworked and fixed, they could be had at some deep discount prices at one time.

The rocket science is where the 90 degree point occurs between the roller assembly and the valve stem. Conventional wisdom says that the roller contact point should make a 90 degree angle to the stem with the valve closed. Mr. Miller's patent says the roller's axle should define this point. The idea being that this reduces side loads on the valve guide and improves tracking. The contact point between the rocker and valve stem changes as the valve moves up and down in its guide. The rocker end is making an arc, its motion is not perpendicular to the stem. So the contact point tends to move from slightly inside (the intake side on a V8) across the center to slightly outside (the exhaust side) and back again. This is not only influenced by the relationship of the contact point to the fulcrum of rotation but also the length of the push-rod. This is why getting the push-rod length correct so it produces the least amount of contact point movement and holds that movement about the center of the valve diameter as possible. There are needless to say several thoughts as to when the center loading should occur. Ideal you can't get as the geometry of the movement offers only the least onerous compromise. Some, if not most, guys like the 1/3-1/3 rule where the contact starts about 1/3 the stem diameter off center to the inside sweeps across the center to 1/3 on the exhaust side and returns again. Others like to set up so the contact point is on center at max lift which is the point of highest spring pressure so any off center load will push the stem hard into the guide. This of course is given the same dimensional limits as everything else at the rocker top so ideal is probably not achievable in the real world. Stem caps can be used to some advantage here as a means to adjust lengths and to provide a larger stage for the contact surface.

I'm rather of the opinion from a theoretical stand point that this is a tempest in a tea pot kind of thing, you're unlikely to find people anchored on one side or the other on mid-lift rockers. Miller's work fine so do Harland Sharp and most everything between that's of quality materials and manufacture.

Quality is where I'd spend my time worrying, there are a lot of cheap knock off rockers out there that result in a real mess when they fail.

Bogie

cobalt327 10-10-2011 10:10 PM

Quote:

Originally Posted by oldbogie
The rocker end is making an arc, its motion is not perpendicular to the stem. So the contact point tends to move from slightly inside (the intake side on a V8) across the center to slightly outside (the exhaust side) and back again. *SNIP* Some, if not most, guys like the 1/3-1/3 rule where the contact starts about 1/3 the stem diameter off center to the inside sweeps across the center to 1/3 on the exhaust side and returns again.

I'm hoping you can clear this up for me. Comp Cams has long had the diagram below posted on their site on valve train geometry.

Do they depict the correct action? It would seem to me that the roller would move towards the intake side of the valve tip the more lift applied, not towards the exhaust side the more lift was applied. Disregard their depiction of where the base circle is in comparison to the mid- and full-lift positions. What I'm concerned with is whether the roller moves towards the intake side or the exhaust side as lift increases.

Thanks in advance.

http://www.cpgnation.com/filehost/fi...m%20A-Lift.JPG

oldbogie 10-11-2011 12:39 PM

Quote:

Originally Posted by cobalt327
I'm hoping you can clear this up for me. Comp Cams has long had the diagram below posted on their site on valve train geometry.

Do they depict the correct action? It would seem to me that the roller would move towards the intake side of the valve tip the more lift applied, not towards the exhaust side the more lift was applied. Disregard their depiction of where the base circle is in comparison to the mid- and full-lift positions. What I'm concerned with is whether the roller moves towards the intake side or the exhaust side as lift increases.

Thanks in advance.

http://www.cpgnation.com/filehost/fi...m%20A-Lift.JPG

This is accurate, there is no perfect solution to this short of a direct acting overhead cam. The length of the push-rod controls the start, mid, and end points of the sweep, which is why its so important got this right assuming that the rocker dimensions are not changeable.

What's happening is the rocker is making a rotation around its fulcrum. At the valve stem on the tip of the rocker it is describing a secant of a circle that moves to a tangent then back to a secant as the rocker presses on the valve stem. A secant is a line that passes inside the perimeter of circle cutting that perimeter in two places. A tangent occurs when the two secant points meet at the same location so the line only touches the perimeter at one place.

The rocker tip forms the perimeter of the circle. The valve stem is the line that can be a secant or tangent depending upon where it intersects the circle described by the rocker. The rocker actually is making two different circles as it moves those being the valve-stem side and the push-rod side. The difference between their radiuses is equal to the lift ratio.

Jim Millers argument is that the side loading on the stem and resulting harmonics is at its minimum when a line that connects the center of rotation of the fulcrum makes a 90 degree angle with the valve stem when that line passes through the roller's axle and that axle is centered on the stem at mid lift. This is not really inconsistent with what the Comp tech site is driving on.

However, conventional design of roller tip rockers Mr. Miller argues passes that line through the contact point which makes an inaccuracy of the roller's movement on the stem equal to the radius of the roller. This is to say that there are two lines of secant and tangent; 1) that of the tip contact point and 2) that of the roller's rotation center. They are not describing the same secant line through the perimeter of the circle of rotation. This difference is a side load on the stem and a rocking motion along the roller's axis if the stem and roller are not meeting perfectly flat to each other, which I rather doubt happens on the best of race engine builds, especially after the first head service.

When I say this is a "tempest in a tea pot"; I mean that with the typical engine with 1.4 to 1.6 ratio rockers and lifts under .5 inch the difference is so small as to have no practical effect. However, with extreme lift cams and/or rocker ratios where the valve is being opened .6 to .8 inch this is something you want to consider as the motions are becoming quite extreme and there gets to be a real risk not only of extreme side loads on the stem but of not being able to keep the contact point on the stem if you?re not very careful.

Bogie

ap72 10-11-2011 12:51 PM

Quote:

Originally Posted by cobalt327
I'm hoping you can clear this up for me. Comp Cams has long had the diagram below posted on their site on valve train geometry.

Do they depict the correct action? It would seem to me that the roller would move towards the intake side of the valve tip the more lift applied, not towards the exhaust side the more lift was applied. Disregard their depiction of where the base circle is in comparison to the mid- and full-lift positions. What I'm concerned with is whether the roller moves towards the intake side or the exhaust side as lift increases.

Thanks in advance.

http://www.cpgnation.com/filehost/fi...m%20A-Lift.JPG

This may or may not be correct depending on your application. If you adjust the valvetrain to give you minimum scrub this is actually incorrect. The roller tip will be furthest to the outside on the valvestem tip during MIDLIFT and will be the furtherest on the inside during zero and peak lift. That is the whole idea behind the midlift method- minimizing the scrub and side loading.

You can do it the way depicted in the picture though, and you usually end up with something like this if you adjust your rocker arms to have a centered wipe pattern rather than the smallest wipe pattern.

There are arguments on both sides, I follow the method of least scrub.

cobalt327 10-11-2011 12:52 PM

Bogie, thanks for taking the time to describe that. I appreciate it.

I often find that I have to think in extremes to get my head around a concept. But when I imagine a mega-lift cam opening the valve via a roller rocker as depicted above, I cannot see the roller riding off of the valve tip on the exhaust side. Instead I see it running off the tip on the intake side. What am I not getting here? :confused:

And again, thanks for your time.

engineczar 10-11-2011 12:56 PM

The short answer for me is that the example shown has a pushrod that is too short.

cobalt327 10-11-2011 02:50 PM

After thinking about this and doodling on paper, I believe the flaw in my thinking is that because the pushrod cup and the rocker roller are not on the same "plane" (maybe not the right term, but hopefully it will still be understandable) w/one another, the roller will describe the motion as depicted in the diagram, and Bogie's description. If the two points were perpendicular(?) to the rocker stud, or if the roller were lower than the p-rod cup, my theory might hold true. But because the roller is positioned above the p-rod cup, the movement is as Comp/Bogie said.
Or not.http://www.chevelles.com/forums/imag...lies/clonk.gif

I do believe that if the lift were high enough that there's a possibility that an 'ordinary' rocker arm might go towards the exhaust side per Comp/Bogie, then at some point actually reverse and move back towards the intake side again. But in practice I doubt this will occur until lifts were enormous and even then the design of the rocker might be able to counter that effect.

ap72 10-11-2011 03:12 PM

Quote:

Originally Posted by cobalt327
After thinking about this and doodling on paper, I believe the flaw in my thinking is that because the pushrod cup and the rocker roller are not on the same "plane" (maybe not the right term, but hopefully it will still be understandable) w/one another, the roller will describe the motion as depicted in the diagram, and Bogie's description. If the two points were perpendicular(?) to the rocker stud, or if the roller were lower than the p-rod cup, my theory might hold true. But because the roller is positioned above the p-rod cup, the movement is as Comp/Bogie said.
Or not.http://www.chevelles.com/forums/imag...lies/clonk.gif

I do believe that if the lift were high enough that there's a possibility that an 'ordinary' rocker arm might go towards the exhaust side per Comp/Bogie, then at some point actually reverse and move back towards the intake side again. But in practice I doubt this will occur until lifts were enormous and even then the design of the rocker might be able to counter that effect.


Imagine standing with your shoulder in plane with the top of the book case, and you swing your arm (straightened) around to slap the top- your action is completely perpendicular to the top of the case. If you lower yourself your action is actually slightly askew to the case and pushing it outward, also the corner of the case will touch further out on your finger tips. If you raise yourself above so your waist is inline with the case and swing again your action is now askew and slightly towards yourself, you again will meet the corner further on out on your finger tips.

Clear as mud right?

millerrockers 10-22-2011 05:07 PM

Wrong -- right -- wrong
 
Quote:

Originally Posted by ap72
This may or may not be correct depending on your application. If you adjust the valvetrain to give you minimum scrub this is actually incorrect. The roller tip will be furthest to the outside on the valvestem tip during MIDLIFT and will be the furtherest on the inside during zero and peak lift. That is the whole idea behind the midlift method- minimizing the scrub and side loading.

You can do it the way depicted in the picture though, and you usually end up with something like this if you adjust your rocker arms to have a centered wipe pattern rather than the smallest wipe pattern.

There are arguments on both sides, I follow the method of least scrub.


The illustration from Comp Cams is not only the WRONG thing you want, it is the worst thing you want. It is the anti-mid-lift scenario. The correct "symptom" that would be illustrated in the valve motion atop the valve tip would be A to B then back to A, there is no C. The roller sweeps out to its farthest point at precise "net" valve MID-LIFT, then rolls BACK to the inside of the valve as it reaches maximum net Valve Lift.

Secondly, any reference to the "middle of the valve" for setting, seeking, or designing is NOT correct, and it is not why MID-LIFT sets up the way it does. I have said it a million times, "where the roller sits atop the valve means nothing, providing it stays atop the valve." Because of the myriad of dimension variables involved, setting mid-lift geometry correctly, AND trying to get the roller in the middle of the valve is nearly impossible. It doesn't matter anyway, PROVIDING you have the rocker set at precise mid-lift.

The whole purpose of MID-LIFT is for CAM timing, NOT reduced wear on the guides, or valves, or minimum sweep atop the valve, or reduced drag coefficients in the rotating valve train. But these are all the "symptoms" that are beneficial, because you get ALL these when you set for mid-lift geometry. The main purpose, is to convert as much of the CAM'S information accurately, through the radial arc process with the least amount of radial converion loss. IT "standardizes" all cam testing data. Without setting the rocker geometry accurately, to mid-lift, you are wasting SEVERAL degress of cam information in the excessive motion of an overarcing pushrod and roller tip

Please NOTE that I said "pushrod" AND "roller tip." All your theories for setting rocker geometry on the valve tip, by measuring the sweep, getting it as least as possible, and making a variety of different little tools to measure this, do NOT have anything to do with what is happening on the other side of the rocker, and the MOST IMPORTANT side: the pushrod cup. This is where all the trigonometry is taking place. THIS is where ALL THREE of the cam's dynamics are either being fully "captured" for translation through the radial process, or LOST -- and the element that determines this is a 90 degree tangent point in the pushrod ball AXIS at precisely "MID-CAM-LIFT".

So when you are setting the valve side with a Comp Cam rocker, or a Jesel, or a (gag) Scorpion rocker, you're NOT setting the pushrod side TOO. You're only setting the valve, and the more important side is still over-arcing, because the position of all the other rockers, compared to the Patented mid-lift design, are TOO high in the body, so the pushrod has already passed through its mid-lift, and it is overarcing trememdously, and the pushrod is moving in out about .050" or .100" -- when it should be only moving about .013" in and out, so its harmonics are like a BASS guitar's E-string, and you've just lost about 6, 8, 10, 12 or more degrees of your camshaft THROUGHOUT the entire valve lift cycle. So that 265 degree cam (@ .050) is now only 255 degrees.

The difference can be felt and seen with an old fashioned needle torque wrench. An engine of bad rocker geometry will typically take 15 to 40 lbs more torque to turn over (without spark plugs of course), than a MID-LIFT system, properly installed. I want to emphasize this last point "properly installed." If you are off by as much as .020" of an inch (1/2 of 1 turn on an adjusting screw) you will lose 2 or 3 degrees of your camshaft. God only knows how many engines are running around, blindly happy because they don't throw their parts out the headers (yet), with .050", or .100" or .150" too long a pushrod (or worse), and stand heights all over the place.

Cam information! Getting it all through the system to the valve, with the least amount of wasted motion, so that a "standard" was set that would measure EACH cam tested without having its differences be diluted by a rocker arm stealing the information.

THAT is why I designed mid-lift. Hope this clears up some of the rhetoric. Good luck! --JM

cobalt327 10-22-2011 05:36 PM

Quote:

Originally Posted by millerrockers
The correct "symptom" that would be illustrated in the valve motion atop the valve tip would be A to B then back to A, there is no C. The roller sweeps out to its farthest point at precise "net" valve MID-LIFT, then rolls BACK to the inside of the valve as it reaches maximum net Valve Lift.

So, if following the mid-lift scenario, at max lift am I correct in thinking the roller should be at a position more towards the intake side of the valve tip as I originally thought?

BTW, the Comp diagram uses "1", "2" and "3" for the positions of the roller across the tip of the valve, not "A", "B" and "C". So is your "A" above = 1, "B"=2 and "C"=3?

Thanks for your time.

eloc431962 10-22-2011 05:42 PM

This is some great info !!!!!!!!!!!!!!
 
Quote:

Originally Posted by millerrockers
The illustration from Comp Cams is not only the WRONG thing you want, it is the worst thing you want. It is the anti-mid-lift scenario. The correct "symptom" that would be illustrated in the valve motion atop the valve tip would be A to B then back to A, there is no C. The roller sweeps out to its farthest point at precise "net" valve MID-LIFT, then rolls BACK to the inside of the valve as it reaches maximum net Valve Lift.

Secondly, any reference to the "middle of the valve" for setting, seeking, or designing is NOT correct, and it is not why MID-LIFT sets up the way it does. I have said it a million times, "where the roller sits atop the valve means nothing, providing it stays atop the valve." Because of the myriad of dimension variables involved, setting mid-lift geometry correctly, AND trying to get the roller in the middle of the valve is nearly impossible. It doesn't matter anyway, PROVIDING you have the rocker set at precise mid-lift.

The whole purpose of MID-LIFT is for CAM timing, NOT reduced wear on the guides, or valves, or minimum sweep atop the valve, or reduced drag coefficients in the rotating valve train. But these are all the "symptoms" that are beneficial, because you get ALL these when you set for mid-lift geometry. The main purpose, is to convert as much of the CAM'S information accurately, through the radial arc process with the least amount of radial converion loss. IT "standardizes" all cam testing data. Without setting the rocker geometry accurately, to mid-lift, you are wasting SEVERAL degress of cam information in the excessive motion of an overarcing pushrod and roller tip

Please NOTE that I said "pushrod" AND "roller tip." All your theories for setting rocker geometry on the valve tip, by measuring the sweep, getting it as least as possible, and making a variety of different little tools to measure this, do NOT have anything to do with what is happening on the other side of the rocker, and the MOST IMPORTANT side: the pushrod cup. This is where all the trigonometry is taking place. THIS is where ALL THREE of the cam's dynamics are either being fully "captured" for translation through the radial process, or LOST -- and the element that determines this is a 90 degree tangent point in the pushrod ball AXIS at precisely "MID-CAM-LIFT".

So when you are setting the valve side with a Comp Cam rocker, or a Jesel, or a (gag) Scorpion rocker, you're NOT setting the pushrod side TOO. You're only setting the valve, and the more important side is still over-arcing, because the position of all the other rockers, compared to the Patented mid-lift design, are TOO high in the body, so the pushrod has already passed through its mid-lift, and it is overarcing trememdously, and the pushrod is moving in out about .050" or .100" -- when it should be only moving about .013" in and out, so its harmonics are like a BASS guitar's E-string, and you've just lost about 6, 8, 10, 12 or more degrees of your camshaft THROUGHOUT the entire valve lift cycle. So that 265 degree cam (@ .050) is now only 255 degrees.

The difference can be felt and seen with an old fashioned needle torque wrench. An engine of bad rocker geometry will typically take 15 to 40 lbs more torque to turn over (without spark plugs of course), than a MID-LIFT system, properly installed. I want to emphasize this last point "properly installed." If you are off by as much as .020" of an inch (1/2 of 1 turn on an adjusting screw) you will lose 2 or 3 degrees of your camshaft. God only knows how many engines are running around, blindly happy because they don't throw their parts out the headers (yet), with .050", or .100" or .150" too long a pushrod (or worse), and stand heights all over the place.

Cam information! Getting it all through the system to the valve, with the least amount of wasted motion, so that a "standard" was set that would measure EACH cam tested without having its differences be diluted by a rocker arm stealing the information.

THAT is why I designed mid-lift. Hope this clears up some of the rhetoric. Good luck! --JM

Now Mr Miller you have me thinking and wondering if i have figured my geometry all wrong and have went with to much length on my push-rods,
I just did a new cam in my engine and the geometry was way off and had to go with a much longer push-rod to make everything sit right.
now i am wondering if i have defeated my purpose. :sweat:



Cole
:pimp:

millerrockers 10-22-2011 05:55 PM

Quote:

Originally Posted by cobalt327
So, if following the mid-lift scenario, at max lift am I correct in thinking the roller should be at a position more towards the intake side of the valve tip as I originally thought?

BTW, the Comp diagram uses "1", "2" and "3" for the positions of the roller across the tip of the valve, not "A", "B" and "C". So is your "A" above = 1, "B"=2 and "C"=3?

Thanks for your time.

Yes, and Yes. I only use an outside cam company link on the MID-LIFT.com web site one time, and it is specifically this illustration at the Comp Cams site, and the link is used under the definition "WRONG GEOMETRY" in the Terms & Definitions page:
http://www.mid-lift.com/TECH/TECH-Definitions.htm

Click on "W" in the ALPHA bar to be taken to this last definition.

I am not trying slam Comp or anyone, but I am still and engine builder at heart, and I hate to see so many guys chasing their tails from BAD INFO from companies that KNOW BETTER.

I might add as I tried to emphasize in the prior post, measuring for what you're setting needs to be done accurately, and you can't do that with chasing symptoms. The roll on the valve, the Smokey Yunick "look at it from the side" routine, and blue-inking the valve tip for a pattern, only gets you close. The easiest, and most precise way to set up, is in the CLOSED valve position, by measuring where the trunnion (or shaft) axis is BELOW the roller tip axis. You want this to be exactly HALF of your NET VL. If you have .600" VL, then the trunnion needs to be .300" BELOW the roller PIN Centerline.

The TRICK (if there is one), is to measure at a PRECISE 90 degree relationship with the valve. The best way to do that, is the valve spring retainer, or the valve stem itself -- but that can only be for a shaft system, where you're setting up the STAND height. That can be done on a bare head on the bench. Then order your pushrods when the heads are all bolted up.

Not trying to do any selling here. Where I am directing you is FREE. So go to the INSTALLED geometry page of MID-LIFT, and look at the same illustration I published in the Lunati catalon in 1988, that remained for 12 years. It uses the technique I mentioned above. It will get the last .003" of an inch accuracy out of your system, and your CAM. Needless to say, you MUST order exactly the correct length pushrod, or it's all a waste of time. :-)

Maybe you've already been here, but here's the link:
http://www.mid-lift.com/TECH/TECH-Installed-G1.htm

ericnova72 10-22-2011 05:55 PM

To help with what Miller is saying, his positions on Comps "1-2-3" drawing would coincide to something like 1-1/2 and 2-1/2,... in between the "1-2" and "2-3" positions Comp gives. Roller should start at 1-1/2, roll out to 2-1/2 at mid lift, and back to near 1-1/2 at full lift.

That's just a rough explanation I put out to try to help people get there head around it., he details it better when you read it through enough times to understand what he is pointing out.

Wish Comp and others would just dump that old 1-2-3 position drawing.

cobalt327 10-22-2011 06:11 PM

Quote:

Originally Posted by millerrockers
Yes, and Yes. I only use an outside cam company link on the MID-LIFT.com web site one time, and it is specifically this illustration at the Comp Cams site, and the link is used under the definition "WRONG GEOMETRY" in the Terms & Definitions page:
http://www.mid-lift.com/TECH/TECH-Definitions.htm

Click on "W" in the ALPHA bar to be taken to this last definition.

I am not trying slam Comp or anyone, but I am still and engine builder at heart, and I hate to see so many guys chasing their tails from BAD INFO from companies that KNOW BETTER.

I might add as I tried to emphasize in the prior post, measuring for what you're setting needs to be done accurately, and you can't do that with chasing symptoms. The roll on the valve, the Smokey Yunick "look at it from the side" routine, and blue-inking the valve tip for a pattern, only gets you close. The easiest, and most precise way to set up, is in the CLOSED valve position, by measuring where the trunnion (or shaft) axis is BELOW the roller tip axis. You want this to be exactly HALF of your NET VL. If you have .600" VL, then the trunnion needs to be .300" BELOW the roller PIN Centerline.

The TRICK (if there is one), is to measure at a PRECISE 90 degree relationship with the valve. The best way to do that, is the valve spring retainer, or the valve stem itself -- but that can only be for a shaft system, where you're setting up the STAND height. That can be done on a bare head on the bench. Then order your pushrods when the heads are all bolted up.

Not trying to do any selling here. Where I am directing you is FREE. So go to the INSTALLED geometry page of MID-LIFT, and look at the same illustration I published in the Lunati catalon in 1988, that remained for 12 years. It uses the technique I mentioned above. It will get the last .003" of an inch accuracy out of your system, and your CAM. Needless to say, you MUST order exactly the correct length pushrod, or it's all a waste of time. :-)

Maybe you've already been here, but here's the link:
http://www.mid-lift.com/TECH/TECH-Installed-G1.htm

This info will no doubt help to give a better understanding of the 'cause and effect' of valve train geometry. Thanks again for your time, it's appreciated.http://www.chevelles.com/forums/imag...s/thumbsup.gif

OT- Good to see you back, ericnova72. :cool:


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