? Valvetrain Geometry ?

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340sFastback said:
Doesn't seem to be a "standard" when it comes to after market rockers. They all seem to be different lengths. The picture I posted above was my Comp Pro Magnum Rockers on my Edelbrock heads.
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Agreed. There is no cookbook that I know of that will tell you which rockers will fit which heads. Valve stem height and mounting perch height and placement will affect the rockers tip placement.

I am setting up for the Crane Retrofit Roller install on my 360 and was going to use ported Iron J heads with a new set of Harland Sharps roller rockers. I had the heads set up with 2.05 valves and with the 1.6xx installed height for the Crans springs along with lash caps, the HS geometry was flawless!! Then I switched to a set of edelbrock heads and diff valves/springs and the HS run off the valves. I would need to modify the shaft mounts to get a reasonable placement on the valve tip.

So I have this new set of nice rockers (only installed for mock-up/measurment on new dry heads) that I can't use. Guess they will go up on classifieds in a few days.

I really like the look of the Comp Magnum rollers but would have to use dbbl ball end pushrods adding to my expense.

Not intending to hijack, but has anyone used the Hughes aluminum rollers rockers on a mostly stock closed chamber Edelbrock head? The pics on their site sure look good but for street/strip application, maybe the steel magnums would be the better ticket? Opinions welcome.
 
I ran across this thread last night and probably would not have checked my engine before I took it apart today. So looking at mine,I seem to have the same issue as John had on his.

I do know that I have had the heads redone once since this engine was originally built many years ago. So if the seats were ground on mine,that might explain why the roller is more towards the outer part of the valve.

Thanks guys,keep up the good info:thumbup:

 
Maybe I just can't see the tip placement very well in the picture, but they look serviceable to me. It also looks like you are already past the end of the max outward travel in the fulcrum, and bigger cam lift would only improve the tip position at max lift.

I ended up grinding my lash caps down about .020 to clear the keepers and have about the same run-out as yours show. I plan to give it a try.
 
I cant see the pics on this PC (work). But I can tell you a huge number of engines suffer from this and are down on power because of it.
 
fishman said:
Are these pics of your motor after you ran it for a while.
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If this question is for me...yes it has run awhile..mostly cruising,as the car had so many other issues I never made a pass on it
 
Is that max lift? If so, and judging by eye with the closed valves, the shafts need a lift...
 
I think it was at max lift,I'll order some shims to raise it and see how that comes out...thanks again
 
This is just my opinion, so all please feel free to correct or ignore any of this.

I am not sure a shim here will help the max lift without hurting 1/2 lift more. You just need to check to make sure you don't go off the reservation (valve tip) at any point in the travel.

The geometry on these rockers is not obvious but this is how I understand it. The arm is longest on the valve (closest to the exhaust side of the head) when the arm-to-shaft angle reaches 90deg relative to the valve tip. Movement either way from this point pulls the tip back toward the intake side. So valve stem height relative to the rocker arm shaft height create the angles that determine how the arm will operate throughout its arc of travel and rocker shaft mount placement and rocker ratio determines the m ax arc of travel.

If your shaft-to-rocker-to-valve angles are already at or near 90deg with no lift, then shims will move the starting placement of the tip further toward exhasut side, but pull it back throughout travel (this is not usually the case with SB performance heads). If the angles are < 90deg at the start and will sweep through 90 during lift, the rocker tip will move toward the exhaust side, then back toward the intake side (more common). The trick in my mind, is a balanced travel on the valve tip but favoring for the best centered position of the tip at max spring pressure. It "seems" like this would be easier on guides and valve deflection.

In this case, if you could lift the shafts straight up in line with the valve then yes it would help max lift. But the angle that the stands are machined at is not 180deg relative to the valve stem, so when you shim the mount point you can also move the rocker further toward the exhaust side. This can result in a net gain of nothing (if you are already past the 90deg angle to the valve tip) because even though the rocker rotates further to cover the shim distance the shim moved the initial placement further toward exhaust so the actual position does not change much it at all. Shims can also affect push rod length. Lash caps effectively make the valves longer and will move the initial contact point of the rocker higher (which can also affect push rod height some) and may or may nor help you depending on the angles involved.

Unfortunatley this is all unique with each head/valve/rocker combo and must be carefully sorted out. If we all had nascar budgets to move our valves or rockers up and down as needed it would be easier. I am usually stuck using the parts I have and making do with the result.

I would be interested to see what you end up with here and of course good luck!
 
Blufie,
I agree, however looking at the pic(which I can no longer see ...back at work...lol), if I draw a line between the centerline of the shaft, and the centerline of the roller on a rocker that is on the base circle (no lift) it is significantly less than 90*. I use teh 1/2 lift method to verify the position of the tip on the stem, and by that pic, the rocker at max lift is too far outside(towards exh side of head) to be healthy at mid lift. It is at mid lift where the tip will be furthest out on the stem. max lift it should be sucked back to the center of the stem. Unfortunatley, like you say, every head is defferent, and in some cases, each valve could be if the valve job was really shoddy. I am picky about my valve work because I hate shims. I use them as a last resort. but in this case, with it all together and running, i think it'sa viable fix so long as things are kept to reasonable thickness. Sometimes a shim of .015 makes a huge difference in the sweep.
 
Thank you both for the reply,I have gone ahead and completely disassembled the engine at this time due to the cracked rear main cap. I will also have to pull the heads apart and freshen them up. I will post pics when it goes back together,and we shall see how it comes out. Thanks again
 
I just finished reading this thread and I want to thank you for the great tech info and up close pics. I have a better understanding of optimal rocker arm geometry in relationship to the valve stem. Thanks again and definately a good read. I would think it deserves a sticky. I wonder how many people just swapped out the rockers and didn't even give it a second thought? (I know I'm in that boat)
 
63dartman said:
I just finished reading this thread and I want to thank you for the great tech info and up close pics. I have a better understanding of optimal rocker arm geometry in relationship to the valve stem. Thanks again and definately a good read. I would think it deserves a sticky. I wonder how many people just swapped out the rockers and didn't even give it a second thought? (I know I'm in that boat)
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I'm with you on this one.....the more I read,the more I understand how stuff like this happens. The engine was probably correct when the original builder finished it. Since then it has got a cam change and since the original builder moved,the heads when freshened up were sent to someone else. It was then my responsibility to make sure that it was set up correctly,but I just assumed everything was correct and slapped it back together. Now I know to check everything,no exceptions
 
Thanks for the comments. Unfortunatley many engines are built by people who don't check any of this the first time (like me when I was 18). Unless the problems are extreme, the engines run... for a while anyway.

I always had some assumption that a $600 set of "cool looking" rocker arms sold by a leading performance company would "fit" and work perfectly (regardless of which valves, mahine work, springs, etc... I had). In fact, that is the trap that speed magazines used to snare many of us with in the past. "So-n-so did such-n-such with these killer parts and made a zillion HP so go right out and buy these parts!!!" A lot of the more popular magazines today do a much better job of giving true project results and good tips/checks to do when trying stuff yourself. You just have to expect that no two re-builds are ever exactly the same, even if stock! Stock rebuilds can just live with a lot more slop than performance engines can.

The bottom line is as you stated. Assume nothing, check everything, and add 10% minimum to your build budget for the extra "fixes" you will need to do for your specific setup.
 
I think lash caps would aleviate most of these problems, Not only do they make your valve slightly longer, they are hardened and they also increase the valve tip area by about 100%. I would always recommend that you run a lash cap with any roller tipped rocker as the contact area is much smaller with the roller than a stamped or static rocker face.
 
I know diff rockers have diff lengths .I thing the harlands are the longest.I went through this on my motor. I also have a set of comps in the for sale section.
 
Pishta, Lash caps will add surface area and as a last resort they could be used. They require matching retainers and only give the rocker tip more area to sweep. With roller cams that is sometimes necesary. But adding area for the sake of keeping the tip away from an edge, is not doing anything to correct the actual path the tip is traversing. So your instability and odd angles are still there.
 
this geometry problem is not a new thing. Running a harlon sharp set up with mine an it has taken alot of time to get it right. Changed pushrod lenth to get a little better angle an keep from rubing. had problems spliting rockers but got some updated ones frome harlon sharp an think i have eliminated this problem. I ajust the valves after every run if possible to keep from dumping a push rod. had to move the hole set up back to keep the rocker from hitting the springs. Best off luck getting yours right.
 
I thought i might update this thread a little,now that i have my heads apart.

The following pictures are the rocker just sitting on the valve, 1/2 of total lift and full lift,which on this cam is .549







As you can see the rocker starts in the middle and rolls almost to the edge.

This is what the tops of the valves were looking like.




If i were to grind the valves,with the margins being so small on these, I think that would further compound my problem. So i did a little checking and found Milodon offers a valve that is a little longer than stock. I don't remember the exact dimension,i left the book at the shop.

Haha,no such thing as just bolting parts on ehh
 
When you say "grind valves" you talking about doing a valve job? If so that would probably make the valve stem sit higher in the head which would improve your geometry.
 
moper said:
Pishta, Lash caps will add surface area and as a last resort they could be used. They require matching retainers and only give the rocker tip more area to sweep. With roller cams that is sometimes necesary. But adding area for the sake of keeping the tip away from an edge, is not doing anything to correct the actual path the tip is traversing. So your instability and odd angles are still there.
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I believe that lash caps also add around .030-.060 to the tip of the valve which simulates a longer valve and thus changes the geometry. You can also usually find lash caps that will work with the valves you have. It is true that they do make some retainers with cap reliefs (esp for hemi's) all you really need is enough valve tip to get the cap to seat without putting pressure on the valve retainers under load. I used some from Crower that were .060 deep and .060 on top and they helped the surface area of my Harland Sharps as well as the pattern.

I will agree that more surface area by itself does not help your actual geometry but it does keep the rocker tips from falling off the side of a valve which is not only noisy, it usually breaks things quick.
 
First of all I want to say that this site and you guys are a treasure trove of information.

Is there any way to tell before you buy the roller rockers if they are appropiate for the application?

While I had planned on buying new pushrods, I had not concidered the possibility that the rockers sold as "for LA engines" would not be in the right place. I will be running Eddy heads and standard length valves. Ryan at Shady Dell will be doing the work, do you think he will be able to tell me which rockers will work?

Guys, I have taught my son that someones knowledge base is like a circle drawn on a piece of paper. Everything you know is contained within the circle. Everything you know that you don't know is the circle. And everything you dont know is outside the circle.

Thanks for making the circle bigger and showing me so much more I dont know.
Andrew
 
blue missile said:
Is there any way to tell before you buy the roller rockers if they are appropiate for the application?
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Not that I am aware of. If it were me, I would decide which rockers are the best design for my setup and then have Ryan try to work out the best geometry WITH those rockers in hand. It won't (and should not) be free, but would be money well spent if you get a solid valvetrain setup. Ryan may be able to vary the installed valve height, modify the pedestal heights, or do other things to get the "best" fit for your rockers. Check with him.

I really wanted to have ShadyDell build a set of heads for my project but I got impatient and bought some "gently used" Eddy's thinking I was getting a deal. The heads were fine, but not for my setup and the re-work and compromises I have made are yet to be tested and thus may end up costing much more in the long run. Patience, test fit, and more patience usually end up with the best results.
 
Blown, that sounds like a plan. If you had seats put in, or ran arger valves, the height of the seat may be out in towards the chamber, making the valve short.
 
Yes 340 I was refererring to a valve job,but I'm afraid after i cut the valves there would be nothing left of a margin.I have a buddy who is a Manley dealer and his going to send me one new intake and exhaust valve to play around with. He said that he did not change any seats out,just cut them the last time he freshened them up for me.When I get them,i'll post some pics and we'll see if there is any difference. Thanks all for your replys
 
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