Pray

iTrader: (7)

I just switched to the Yella Terra RR's (which are bad butt pieces) from the stock rockers and a strange thing happend. I set them up perfectly with the shims. .060" wipe pattern right in the middle of the valve stem. They came to 25lbs tq at 1/2 a turn lifter pre-load. Here is the strange part. I lost an inch of idle vacuum. I went from high 10"hg low 11"hg to high 9"hg. At first I thought I messed them up but now I am thinking that the lower vacuum is due to the propper geometry and the valves opening further than before. Am I on the right track with this? When I had the stock rockers on there it was taking me about a turn or so to get 22lbs tq. I never did check the wipe pattern. I did also have to lean things out at WOT which lead me to think I was making less power. It takes more fuel to make more power doesn't it? I lost about three % on my VE table to get the fuel correct. Has any one experienced these things with installing rocker arms?

Brett

vettenuts

iTrader: (4)

I don't have mine running yet, but I just set them up on the work bench with my new AFR heads. The wipe pattern is pretty much perfect. I am not sure you can even get a good wipe pattern with the stockers and aftermarket cams/lifts. I would check the lifter preload with an adjustable pushrod though to make sure you have it correct and the valves are being held open. It could also be the rockers come off the seat faster than stock, which I believe is 1.54 ratio. I know the Cranes come off the seat fast, not sure on the YT's though but it wouldn't surprise me if they came off faster than stock and made the cam appear to have a tad more duration. Faster rocker motion will increase the size of the overlap triangle.

Pray

iTrader: (7)

Well I know the stockers are 1.7 just like the YT's. I am not sure if you could get a readable wipe pattern with the stockers either. Due to the flat nature of the metal. How did you check your wipe pattern on a work bench? Doesn't the push rod length effect the wipe pattern? Plus you have to collapse the spring. I set up the pre-load according to YT's instruction. Get zero lash and a half to three quarter turn and you are perfect. More than a turn and a half and you have to run the shims. Which I had to do. That leads me to believe that my pushrods were too long to begin with. So my prior geometry was probably off some. Hopefully these things were worth the last 10rwhp I was short of hitting the 500rw mark.

ArKay99

iTrader: (1)

Essentially what vettenuts is saying by 'on the bench' is:
Take your heads and replace the intake and exhaust springs with lightweight checker springs. With no pushrod on the rocker it will lay on the valve tip and you can lift it a couple hundred thousands of an inch off the valve tip. With the rocker lifted off the valve tip color in the valve tip with a black Sharpie. Then lay it on the valve tip. Then get a dial indicator and set it up to the proper angle and depth on the top of ther roller tip. Then push down on the roller until the guage reads the same as the cam max lift, then let up. Do this a couple times and you will see the wipe pattern as it would be in the car. As you add height to the rocker seat the pattern will move towards the exhaust and as you remove it it will move towards the intake. The idea is to get it to lie just to the exhaust side with the valve fully up, and as it pushes the valve down it will 'walk' across the valve tip towards the intake and end up just a little on the intake side. This will give a narrow line centered on the valve tip.

One other thing is once you have bottomed out the rocker seat mounting bolt to the boss it doesn't matter how much torque you put on the bolt, you won't change the preload any more. 22 ft/lbs. is just about right. The only way to change preload after you set the rocker height is to change your pushrod length.

My guess is since you shimmed the rocker stand .060" higher you have reduced your preload and need a longer pushrod to maintain the proper preload.

You can do this on the car. You just need to make sure the piston is at TDC and use a good tool to compress the spring to swap to the checker springs. Once swapped move the piston down the hole a bit so you don't collide with it and take your measurements. It's just easier on the bench if your heads aren't mounted. If they are it's gonna beat on your back a bit.

I just did this with my Jesel's and found a huge problem looming so I bought a set of light weight YT's and will be installing those when they arrive on Monday.

vettenuts

iTrader: (4)

Here is how I did it: Link

vettenuts

iTrader: (4)

Actually the rocker ratio isn't constant. The stock rockers come off the seat at 1.54 and reach 1.7 at about 0.300 lift. I'm not sure on the YT's but I would bet willing to be they are more like the Cranes and come off the seat at a higher ratio. If you go to Crane or Vinci's web site, they explain how the rocker can affect the overlap triangle, that may be what you are seeing but I would also thoroughly go over your set. Sounds like you have the geometry nailed so verify your lifter preload.

KCS

iTrader: (20)

Correct, the change in vacuum may just be from the increase in RR throughout the lift range area under the curve. There are different thoughts on "proper" rocker geometry, which all effect peak lift, average lift, and even opening/closing velocities. Jim Miller (of Pratt&Miller I think) has alot of really good info on the subject on his page:

http://www.mid-lift.com

bearcatt

iTrader: (41)

Sometimes ignorance is bliss.

This link makes it seem easy.
http://ls1howto.com/index.php?article=21

After browsing the links posted in this thread ...

http://www.mid-lift.com
http://forums.corvetteforum.com/show....php?t=1935010


... so much for ignorance if you want precision and perfection.



.

Pray

iTrader: (7)

Thanks for the posts guys. Now I understand what Vett is talking about with the bench thing. I am going to do that for my next set of heads. It looks like on non adjustable valve train you don't need a push rod for geometry. You just need it for preload. My wipe pattern looks just like the pick you posted in your other thread Vette. Would the bench method work for an adjustable valve train? I am assuming the push rod becomes a vital part in that equation.

I usually set up the rockers at the normal 22ftlbs, but I just wanted to follow YT's instructions to the letter since they manufacture the rocker.

bearcatt

iTrader: (41)

vettenuts,

Why not post your " Setting the Rocker Wipe Pattern " on LS1 Tech ?

Perhaps it can become a sticky.

Here's a formula that make sense to me.

For starters, follow vettenuts procedure on the bench.

Then with heads installed on the car, use a Pushrod Length Checker.
http://www.thunderracing.com/catalog...&vid=3&pcid=17

And also there is the procedure for adjusting preload.
http://www.hardcorels1.com/vbulletin...read.php?t=622

Apparently, it appears that rocker geometry and preload are two
different entities, allthough they both seem to go hand in hand.




.

vettenuts

iTrader: (4)

I have an adjustable valve train on the car right now. I set that up on the work bench as well. You're correct, pushrod will affect the geometry for an adjustable setup. To do this on the workbench, you need a measurement you can repeat for rocker height when you install the heads on the car and measure for pushrod length. I did this with Crane rockers and used the depth of the stud inside the adjusting nut as my measurement. I found that there was a small range of depth measurements that provided an acceptable wipe pattern on the work bench. Then when I put the heads on the car, I set the rocker and adjustable pushrod in place at zero lash with the nut high and then low on the range that provided a good wipe. From there, you have to figure out what pushrod length will provide the correct preload such that when the lifter is preloaded the adjusting nut ends up within the measured range (original bench measured stud depth).

I hope this makes sense, kind of hard to explain without pictures.

Pray

iTrader: (7)

I got it. You just confirmed what I was thinking about last night after I made my post. Rocker arm geometry just got alot easier. This topic should be a sticky.

vettenuts

iTrader: (4)

Just uploaded the photo's, hope this helps further clarify what I did.