Rocker Arm Geometry - Super Chevy Magazine

The first step is to determine the maximum valve lift generated by the camshaft and to record the value. To do this, you will need to fixture a dial indicator to the valve stem with either a bracket or magnetic stand. If you do not have these tools you can still check the rocker arm geometry by eye, but SUPER CHEVY does not recommend it.

The first step is to determine the maximum valve lift generated by the camshaft and to rec

One of the most common mistakes when building a Chevy engine is neglecting to check the rocker arm geometry. This is usually due to the name of the procedure being misleading and implying the application of higher math. What is required is to check the position of the rocker arm tip on the valve stem during the opening event. The procedure is quite simple and if an error is discovered, it is easily corrected.

Whenever the block or cylinder head deck is machined, the distance to the valve lifter will be altered and the push rod length will need to be modified to keep the geometric angle correct. Additional causes for error are a change in valve lifter style and height, the length of the valve stem, the installed height of the valve, the depth of the spring pocket in the cylinder head, and the design of the rocker arm.

Checking the rocker arm geometry should be a step whenever assembling an engine, even if standard stamped-steel rockers are used.

Follow along as SUPER CHEVY takes the mystery out of this procedure.

With the cam on the base circle (valve closed) the center of the roller rocker should be just shy of the middle of the valve stem as seen in this photo. At this time zero the dial indicator.
With the cam on the base circle (valve closed) the center of the roller rocker should be j
RaceKrafters Machine is planning on marketing a tool to easily measure the rocker arm's travel over the stem of the valve. Pricing has not yet been determined at press time. It will consist of a dial indicator with a mounting bracket made from a valve retainer. The travel of the rocker arm from a closed valve position to one-half maximum valve lift should be less than 0.050 inch. If this tool is not used, you need to securely hold the dial indicator on the tip of the rocker arm.
RaceKrafters Machine is planning on marketing a tool to easily measure the rocker arm's tr
Adjust the push rod length to achieve the desired position of the rocker arm on the valve stem and repeat the procedure. Once the proper length is determined remove the adjustable push rod and measure it with a caliper. Locate a push rod that is within 0.050 inch of the proper length. Repeat the procedure for the other valve. Always recheck the geometry when the new push rods are installed.
Adjust the push rod length to achieve the desired position of the rocker arm on the valve

The steps are the same with stamped steel rocker arms but they are more forgiving of errors in geometry.
The steps are the same with stamped steel rocker arms but they are more forgiving of error
Either turn the engine over by hand or have some one bump the starter until one-half maximum valve lift is reached. If the rocker arm geometry is correct, the roller should be in the middle of the valve stem or just slightly to the far side of there.
Either turn the engine over by hand or have some one bump the starter until one-half maxim
The dial indicator on our subject engine read 0.046 inch. Just at the threshold for maximum movement. But we did not like where the roller sat on the valve stem when the lifter was on the base circle of the cam. It was already past the center. This indicated an error in geometry that was being compounded by excessive push rod length.
The dial indicator on our subject engine read 0.046 inch. Just at the threshold for maximu