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Discussion Starter #21
Is it really necessary to use a shim for the pre-load? Why not just add .025-.050 to whatever measurement at zero lash achieves the best pattern? Shims just seems to complicate things as I believe they alter the sweep when the rocker arm now sits at a higher position. Stud and adjustable rocker arms are much simpler and using the mid-lift measurement made my life easier too.
I think some of the confusion on this comes from the difference in the engine builder's situation. If you read the instructions that came with my Scorpion roller rockers, it says to add shims if you get more than 1 full turn when torquing them to 20ft/lbs. This I believe, is intended for a builder that is not changing pushrods and is not concerned about geometry.
I have to buy hardened pushrods anyway. Since I have both adjustments available to me, why not do it the best I can?
Roller rockers manufacturers should explain this in their instructions better cause I'm guessing it adds to people's confusion.
 

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You don't use the shim to set your preload. Shim is used to get the geometry. You are correct you add the .025-.050 to the pushrod length at zero lash to get your desired pre load.

I don't think anywhere did we state to get preload by adjusting shims?

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I read the posts too fast and misunderstood what was being said. Thank you for bringing it up, as I re-read again and got what was being said. Damn it...needed more coffee!
 

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Mid-lift method is best. Centering is not what your're concerned with using the mid-lift method. Only if the distance from the fulcrum to the center of the valve tip is the exact same as that distance on your rocker arm will you be centered - and then only at half lift. It should actually be biased toward the exhaust side somewhat at half lift. Mid-lift method will show a pattern that is often not exactly centered, which is fine.
 

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You want the sweep as close to the center of the valve and as small as possible. It takes time, but you can fine tune it. This was with .625 lift
1054462
 

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Discussion Starter #26
Centering is not adjustable though - it's baked into the rocker arm.
I think you mean centering is not adjustable if you still want to prioritize minimum roller tip sweep. One of the few things that has been consistent, at least with my set up, is adding shims to my pedestal moves the witness mark more toward the exhaust side of the valve tip. At least it did until I got to like .100 worth of shims.
I'm going to make a steel strap to fix to the head using the valve cover bolts holes. Then I can use my magnetic base dial indicator and see what mid-lift looks like with various combinations of shims.
 

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Formerly LSNotch
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I still don't like the idea of using shims. LS engines uses pedestal style rocker arms and I have never heard of anyone using shims. I think shims are used when you are bound to a specific size pushrod, but I could be wrong in assuming this as another poster explained that is used to achieve a better sweep.
 

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Raising or lowering the rocker will move the tip on the valve. I wouldn't neccessary move the tip location at the expense of a wide sweep. But you should be able to find a nice balance.
There is nothing wrong with using shims. Sometimes to do it right you might have to mill the rocker pad on the head to lower them.
 

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I think you mean centering is not adjustable if you still want to prioritize minimum roller tip sweep. One of the few things that has been consistent, at least with my set up, is adding shims to my pedestal moves the witness mark more toward the exhaust side of the valve tip. At least it did until I got to like .100 worth of shims.
I'm going to make a steel strap to fix to the head using the valve cover bolts holes. Then I can use my magnetic base dial indicator and see what mid-lift looks like with various combinations of shims.
Yeah, maybe "with the geometry set up correctly, the location of the witness mark on the valve tip is what it is, unless you can adjust the fulcrum point" (some shaft systems allow for this.) Usually best geometry biases the mark more toward the exhaust side.

BTW, I always used shims with my 1.7:1 Cobra pedestal rockers. The minute you put an aftermarket rocker in there or shave the heads or change head gasket thickness, the correct way to get it back to where it should be (if preload is off) is to shim it.
 

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Discussion Starter #30
So I learned a lot today, answered some of my questions, but I also have new questions. I got a mounting strap set up on my head and then set up my dial indicator. I started with no shims and push rods at zero lash with the solid lifter and light springs still installed.

I measured the total lift with each set up, calculated half lift, found it, and used my adjustable square to eyeball how close the trunnion centerline and roller tip centerline were to being perpendicular to the valve stem. I liked this method because my results were very consistent and every additional shim showed a definitive change like it should.

The cliff notes are as follows:

With no shims I got .568 of total lift and not even close to looking perpendicular at half lift

With 1- .040 shim I got .573 total lift and a little improvement on the half lift angle

I skipped to 3 .040 (.120) shims and got .579 total lift and more improvement on the angle

With 4 .040 (.160) shims I got .581 total lift and more improvement on the angle

With 5 .040 (.200) shims I got .583 total lift and really close to the desired 90 degree angle with the valve stem

With 6 .040 (.240) shims I got .587 total lift and a perfect 90 degree angle with the valve stem

After I got to 6 shims, I noticed pushrod to roller rocker clearance had become a problem as I couldn't even get a .010 feeler gauge between the pushrod and the edge of the rocker. I decided to retest the 4, 5, and 6 shim set up while checking pushrod/rocker clearance and also using the marker sweep method for the heck of it.

It wasn't until I got down to 4 shims (.160), that I could slide the .010 feeler gauge between the pushrod and rocker again. The marker sweep with the 4 shims was not bad (between .060-.070 favoring the exhaust side).

The best sweep was .056 with 6 shims which I believe confirms that the half lift method does indeed find the shortest, most efficient sweep. This did put it really close to the edge of the valve stem on the exhaust side.

I'll add my pictures to the next post for a visual. I guess the big question I have is how much clearance between the pushrod and rocker body do I need to be safe to run?
 

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Discussion Starter #33
So if what I'm seeing is right, I'm thinking I should do the same procedure for the exhaust rocker. Once I see how much shim would be required there, I'll make custom thickness shims to install under the channels and just add shims above the channel as needed to make up the difference between the intake/exhaust. Then I'll have my friend who is good on a mill, remove rocker arm material from all of them to gain the needed clearance for the pushrods.

Then I'll check thread engagement and likely source new, longer, rocker holddown cap screws to compensate for the added pedestal height.
 

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So if what I'm seeing is right, I'm thinking I should do the same procedure for the exhaust rocker. Once I see how much shim would be required there, I'll make custom thickness shims to install under the channels and just add shims above the channel as needed to make up the difference between the intake/exhaust.

Then I'll have my friend who is good on a mill, remove rocker arm material from all of them to gain the needed clearance for the pushrods.

Then I'll check thread engagement and likely source new, longer, rocker holddown cap screws to compensate for the added pedestal height.
I recently had the clearance issue with rocker to pushrod on my FTI cam setup too. My lift is .600” and I have stud mounted rockers so I adjusted my pushrod length to give myself clearance while trying to keep the narrowest pattern. If you take material off the rocker body you will void your lifetime warranty, just something to keep in mind.
1054575
55BCFB7F-D3F0-4D2A-AFD2-5ECD684454AB.jpeg
A pic of my sweep pattern.
 

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Discussion Starter #35
I recently had the clearance issue with rocker to pushrod on my FTI cam setup too. My lift is .600” and I have stud mounted rockers so I adjusted my pushrod length to give myself clearance while trying to keep the narrowest pattern. If you take material off the rocker body you will void your lifetime warranty, just something to keep in mind. View attachment 1054575 View attachment 1054575 A pic of my sweep pattern.
That's true, but since I have pedestals, my options are limited. If I change valve stem height, I'll need new springs and things with get expensive fast. I'd rather risk a $280 set of rockers.

I'd also rather modify the rockers slightly than risk ruining my valve guides on the heads.

I'd like to hear from anyone that ran a set up that they had to shim the pedestals excessively to get good valvetrain geometry. What should I be concerned with other than fastener length and valve cover clearance?
 

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My bad I guess I got you off on a tangent and an all out effort to redesign your system. I was afraid this might happen once I posted it. That is why I had stated it is more for the reference that some times the parts you have will not let you achieve your end goal. The issue you are facing is what cougar5.0 had tried to point out the fact that you distance from the roller to the fulcrum are not the correct distance possibly the pushrod side as well. You see those rockers were designed off a stock head, stock valve length, stock geometry, stock cam profile. Not Mid Lift theory, So if any of this changes it then becomes a compromise. Which you may not be able to resolve or obtain perfection with the parts you have.

Read thru the post I linked below. This will hopefully answer alot of your question without me having to re type it.
Before you go and machined on your new rockers i would try a few different rockers to get where you want to be. But unfortunately as you stated above if you truly want to get the geometry right it might start to cost some more money and swaping parts along with a good bit of time.
This is all the things customers don't understand when they complain about why things cost so much.

Take a look at this post I hope it should help you out some.


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I do seem to be getting more consistent witnesses marks with the solid lifter. Unfortunately, I'm consistently getting pretty wide sweeps (around .100) with no shims or any combination of shims. Adding shims pushes the sweep closer to the exhaust, but doesn't seem to change its width.
I feel like I've searched for and read nearly every piece of info on this process on the internet. Some say preload is set by the shims, others say it's set by pushrod length. I know I'm not going to be able to get things perfect, especially working with a pedestal setup. I just don't want to chew up valve guides in short order.
I have done this a number of times. I don't know where you are at this stage. but, what I see as your last "mark" looks good. Check your exhaust valve too. If the same, I would say you are "good to go". The rule of thumb, I've followed is mid stem and approximate. .070" wide. If your are building a precision Indy car engine, maybe pay more attention to detail, but, for my money if this is a cruiser, go with it and move on....
 

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Discussion Starter #38
My bad I guess I got you off on a tangent and an all out effort to redesign your system. I was afraid this might happen once I posted it. That is why I had stated it is more for the reference that some times the parts you have will not let you achieve your end goal. The issue you are facing is what cougar5.0 had tried to point out the fact that you distance from the roller to the fulcrum are not the correct distance possibly the pushrod side as well. You see those rockers were designed off a stock head, stock valve length, stock geometry, stock cam profile. Not Mid Lift theory, So if any of this changes it then becomes a compromise. Which you may not be able to resolve or obtain perfection with the parts you have.

Read thru the post I linked below. This will hopefully answer alot of your question without me having to re type it.
Before you go and machined on your new rockers i would try a few different rockers to get where you want to be. But unfortunately as you stated above if you truly want to get the geometry right it might start to cost some more money and swaping parts along with a good bit of time.
This is all the things customers don't understand when they complain about why things cost so much.

Take a look at this post I hope it should help you out some.


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Thanks for the info, I actually had already stumbled across that thread before I ever posted this one. I've tried to read every post pertaining to this topic.

I'm ok with not reaching perfection with my current parts. I just want to get it the best I can with what I already have. It would be nice to have access to speed shop parts laying around so I could experiment with different roller rockers. However, unless someone could tell me with absolute certainty that a certain different rocker would make everything perfect, its just gambling with more money.

Your post motivated me to go ahead and set up my dial indicator and try the half-lift method. I'm glad I did as I feel I will get things closer now.
 

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Discussion Starter #39
I have done this a number of times. I don't know where you are at this stage. but, what I see as your last "mark" looks good. Check your exhaust valve too. If the same, I would say you are "good to go". The rule of thumb, I've followed is mid stem and approximate. .070" wide. If your are building a precision Indy car engine, maybe pay more attention to detail, but, for my money if this is a cruiser, go with it and move on....
I agree, and it is a cruiser. I'm admittedly paranoid about missing something and ruining my expensive parts. I'm happy with the way it checks out as long as shimming the pedestal .240 doesn't cause me more problems that I'm not aware of.
 

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Discussion Starter #40
I did some searches with "rocker arm clearancing" in the text bar and came across a few great threads that I had previously missed.
The second post of this one: https://www.corral.net/threads/pushrod-length-checking-and-clearance.2480302/
Woody shared a picture of clearancing done on the back of the rocker arm. It's good to know this practice is not unheard of.

I also turned up some info saying that Trick Flow and Comp magnums have more pushrod clearance on the backside of the rocker, but I can't find anyplace that sells those in the pedestal mount design anyway.

My searching also found that a board member found out from calling Comp cams that .030 of clearance is the recommended minimum.
 
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