Because I have a relatively high lift Lingenfelter GT-11 cam, I decided to upgrade the rocker arms to the Yella Terra Ultra Lite. The cam specs are 215/231 degree duration @ .050" with and .631"/644" lift and118* LSA. I noticed a random "tick-tick", so I felt it was time to check out the rocker arms and make a change if necessary after 10,000 miles.

Here are some of the photos.

1) Yella Terra Ultra Lite roller rockers unpacked, cleaned and ready to install. I first soaked and shook the new Yella Terra's in a plastic bucket filled half way up with mineral spirits. I did this to clean out any left over machine oil and small metal shavings left over from the machining process. I found small aluminum chips in the bucket and the roller tips seemed to move much more smoothly so it was worth doing. Two rocker arms were rubbing slightly on the shaft "C" clips so I pressed in the fulcrum roller bearings a few thousands to get them to provide clearance. Before installation, I soaked them overnight in engine oil to lubricate the roller bearings.



2) Comparison of the new rockers on the left and the OEM rockers on the right. Although the Yella Terras look huge, they are light weight aluminum. The center fulcrum bearing is a lot bigger in diameter but since the center shaft does not move, it does not add significant reciprocating mass. Pairs of rockers are on a common shaft which keeps them aligned and reduces deflection due to the increased stress from the more aggressive GT-11 cam.



3) Here is a shot of the OEM rocker that was twisted. Each individual OEM rockers pivot on its own bearing and bolts into a semi-circle saddle on a stand-off strip running the length of the head. Apparently, the OEM saddle got twisted some how causing the rocker to be mis-aligned with the valve. Left alone, I think it may cause more valve guide wear than normal.



4) Here is a picture of the normal wear pattern on an OEM rocker. Notice it is evenly worn although the wear pattern at maximum lift is close to the nose.



5) Here is a picture of abnormal wear which appeared on 4 OEM rockers. Notice the half-moon shaped groove starting to develop near the nose of the rocker. The wear on the rocker was significant and don't think this is good. Perhaps this was the source of occasion louder tick-tick than normal.

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Before I started the installation, I made sure I understood how to properly set them up. There is a lot of bad information out there so I be careful.

When buying new rockers, make sure to also get an adjustable push rod length checker. Comp Cam sells them for $20. You need this to figure out the both the rocker arm shims and push rod length.

The Yella Terra comes with 16 .040" shim washers but you may need difference thickness shims from McMaster-Carr.

If the new rocker arm is set up too low, the tip pushes contacts the intake side of the valve first and sweeps too far over the valve stem. If the rocker arm is too high, it will contact the valve stem on the exhaust side first and sweep toward the intake side and will also be wide. The impact can be excessive valve guide wear. The rocker arm sweep pattern should be over the center of the valve stem and as narrow a sweep as possible to keep the side thrust on the valve guides to the minimum. See the photo below.



A lot of folks don't understand the importance of getting the rocker arm geometry correct first. At the bottom of this thread are links to the Comp Cam website that will help explain it.

The push rod length is only to get the correct lifter pre-load. Each rocker arm manufacturer has their own procedure but Yella Terra's say it should be between 1/4 to 1 full turn after zero lash.

Do not even think about the determining the final push rod length until the rocker arm height is right or it will be wrong. Don't listen to those that say always use 7.xxx inch push rods. The only way to do it right is to follow the manufacturer's set up procedure.

COMP CAM PUSH ROD INFO

COMP CAM VALVE TRAIN GEOMETRY

 

Very interesting Mez, have you run the car yet with the new rockers installed?

Nice write-up!

 

I drove it around hot central Texas yesterday. Here is a video at idle. Not silent but the random louder 'tick-tick' is gone. The video was made using my iPhone 3Gs by the way. Just have to keep my finger off the mic.

 

So what pushrod length did you end up with?

 

For my set up, the correct length worked out to be 7.450 inch. But my heads have been reworked with non-stock valves so don't take this to mean that is the right length for you. Just remember: First establish the rocker arm height to get the sweep pattern centered on the valve tip then get the push rod length for the correct lifter pre-load.

I learned a lot during my research and it really was not too difficult. I would strongly recommend anyone with an after market high-lift cam look seriously at upgrading their rockers arms and push rods, too.

 

sorry but, im pretty sure the preload is for the LIFTERS not the rockerarms..

each turn on a rocker bolt = 0.047".

stock is 0.100 as i mesured before i did my cam

best ive found is around 0.080 which prevents lifter from pumping up from 7k rpm shifts.. and has no ticking noise.

-Carl

 

Yes, of course...but where did I say rocker arm preload??? I just reviewed the thread, and did not see where it was stated incorrectly.

 

First off, nice write-up Mez

Carl, not sure what you were reading, but I believe Mez stated it correctly!
As far as proper preload, if you are using OEM lifters, this chart shows what the preload should be. If you are using OTHER than OEM, check with the supplier. In this chart, the last part number is the current lifter as of today.