[TransAm 474]

Good Eveing everyone, we are getting ready to check Rocker Geometry and measure for Pushrod length. We watched the Straub video that has been posted here before, and it is very interesting, and it shows you how to set the proper Rocker Geometry and then measure for the correct Pushrod length using the half lift method. In the video they are using a full roller rocker, and drawing an imaginary line through the center of the trunion and center of the roller wheel axle, then adjusting the Rocker so that the line is at 90° to the valve tip when the camshaft is at the mid lift point. After that is established, they then measure for correct Pushrod length. My question is, does anybody have any tips on using this same method, but with the use of the stock style Stamped Rocker, instead of a full roller rocker?

[1968GTO421]

Excellent question. Do you know if the slot on the stock 1.5 ratio rocker will handle the lift on the Voodoo 704 (Valve Lift (Int/Exh): .504/.527). I know some of my brother's Chevy friends have used a file to lengthen the slot on stock Chevy rockers to handle a high lift cam but I wonder if this would greatly shorten the life of the rocker. There are long slot rockers available for Chevies but not Pontiacs. To some extent this would affect finding the center line to use the Straub method, (Ah, life is always full of such "easy" problems.)

[OG68]

I copied this procedure and used it when I checked my pushrods. I can't remember where I got it from but probably from here. My apologies for not giving credit to the author.

Using a spare rocker stud, the rocker and ball and following the procedure below you can visually estimate where the fulcrum point is. Rotate the rocker back and forth and observe what part of the rocker isn't moving you can get an idea.

This is the references to pay attention to for setting a SHOE tip rocker arm for your net valve lift. As mentioned, finding the centerline of the fulcrum’s rotation is required first since this cutaway only shows where the axis would be. This is not easily seen on the outside of a stamped or cast rocker body so, you need to simulate this rotation and make a mark to reference to.




Finding the axis is not easy. Setting it by the same rules is best simply for standardizing one cam to another. Only your reference is the actual contact point of the pad itself. When it is at mid-lift, you will have a 90 degree relationship between the tip of the valve and the center of rotation for the rocker arm. But finding that center can be tricky, because these are usually ball fulcrum rockers, and they are surrounded by the stamped metal that has no clear axis to it. One solution is to put a stud upside down in a vise and rotate it carefully while observing the fixed point on its side that mostly represents where the center is, then making a little felt tip pen mark. This would then be set exactly half of your net valve lift below the valve tip in the closed position. It’s not as accurate as fixed points to set calipers against, but it will get you very close if you have patience and a sharp eye; and with the shoe tip rockers, the amount of error you might be off will have no measurable effect in cam efficiency as it would with the needle bearing roller tip rockers.

[pastry_chef]

Originally Posted by OG68

II can't remember where I got it from but probably from here. My apologies for not giving credit to the author.

Jim Miller, article may be seen here.
http://www.sbintl.com/tech_library/a...m_geometry.pdf

[TransAm 474]

Originally Posted by 1968GTO421

Excellent question. Do you know if the slot on the stock 1.5 ratio rocker will handle the lift on the Voodoo 704 (Valve Lift (Int/Exh): .504/.527). I know some of my brother's Chevy friends have used a file to lengthen the slot on stock Chevy rockers to handle a high lift cam but I wonder if this would greatly shorten the life of the rocker. There are long slot rockers available for Chevies but not Pontiacs. To some extent this would affect finding the center line to use the Straub method, (Ah, life is always full of such "easy" problems.)

The rockers that we are using are Comp Cams 1251-16, stamped steel 1.5. I'm not sure if they have a longer slot or not, but we will check for any bind on the stud for sure. Seems like I remember Ken Crocie saying that he has used the stock pontiac 1.5 rocker at .550" lift without any problems, but I suppose things can vary from engine to engine. I read someone else on here during my earch running a .565" lift hydraulic roller with stock pontiac 1.5's as well.

[TransAm 474]

Originally Posted by OG68

I copied this procedure and used it when I checked my pushrods. I can't remember where I got it from but probably from here. My apologies for not giving credit to the author.

Using a spare rocker stud, the rocker and ball and following the procedure below you can visually estimate where the fulcrum point is. Rotate the rocker back and forth and observe what part of the rocker isn't moving you can get an idea.

This is the references to pay attention to for setting a SHOE tip rocker arm for your net valve lift. As mentioned, finding the centerline of the fulcrum’s rotation is required first since this cutaway only shows where the axis would be. This is not easily seen on the outside of a stamped or cast rocker body so, you need to simulate this rotation and make a mark to reference to.




Finding the axis is not easy. Setting it by the same rules is best simply for standardizing one cam to another. Only your reference is the actual contact point of the pad itself. When it is at mid-lift, you will have a 90 degree relationship between the tip of the valve and the center of rotation for the rocker arm. But finding that center can be tricky, because these are usually ball fulcrum rockers, and they are surrounded by the stamped metal that has no clear axis to it. One solution is to put a stud upside down in a vise and rotate it carefully while observing the fixed point on its side that mostly represents where the center is, then making a little felt tip pen mark. This would then be set exactly half of your net valve lift below the valve tip in the closed position. It’s not as accurate as fixed points to set calipers against, but it will get you very close if you have patience and a sharp eye; and with the shoe tip rockers, the amount of error you might be off will have no measurable effect in cam efficiency as it would with the needle bearing roller tip rockers.

Thank You for sharing!

[steve25]

HO racings 65 Tempist 326 cid drag car ran stock rockers up to 8000 rpm without issue!

The only issue is that you have to check thru a number of sets of them to find 16 of them that average out real close 1.5 or 1.65 if that's what your looking for.

[1968GTO421]

Originally Posted by pastry_chef

Jim Miller, article may be seen here.
http://www.sbintl.com/tech_library/a...m_geometry.pdf

Thank you PC. Very interesting article (and long). I'm printing it out to read and re-read. Too much great info to miss anything. Thanks again for finding it.

[John Milner]

Originally Posted by 1968GTO421

Excellent question. Do you know if the slot on the stock 1.5 ratio rocker will handle the lift on the Voodoo 704 (Valve Lift (Int/Exh): .504/.527). I know some of my brother's Chevy friends have used a file to lengthen the slot on stock Chevy rockers to handle a high lift cam but I wonder if this would greatly shorten the life of the rocker. There are long slot rockers available for Chevies but not Pontiacs. To some extent this would affect finding the center line to use the Straub method, (Ah, life is always full of such "easy" problems.)

I am currently running stock rockers with the 704 Lunati cam. I had enough clearance to where I really didn't need to lengthen the slot.