When establishing geometry, we use a stand height gage. This gage allows you to establish the geometry quickly. The reason we use this gage is it is a known dimension. All of our gages are designed for a specific lift 0.550”, 0.650”, 0.750”, 0.850” and 1.000” lift. This number will be stamped right on the side on the gage.
This helps establish the tip to shaft relationship between the rocker arm and the valve. The two things that have an effect on this is lift at the valve and valve length. The valve length is the first thing you are compensating for when using the gage. Once the stand has been shimmed so that the shaft touches the gage, you will make a lift compensation. You will raise or lower the stand half the difference between the gage lift number and the actual lift at the valve. If you have greater lift than the gage you will lower the stand, if your lift is less than the gage you will raise the stand.
Example: If you had 0.700” gross lift at the valve and are using the 0.650” gage you would shim the stand to the gage and then remove 0.025” shim from under the stand to compensate for half the difference between 0.700” and 0.650”. If you have the opposite issue with the lift and gage you would raise the stand 0.025”. So if the gage was for 0.750” and gross lift is still 0.700” you would shim the stand till it touched, then raise it an additional 0.025”.
The reason we have you raise or lower the stand half the difference is it will split the roller tip travel on the valve stem over the full lift cycle.
If your stand is requiring more shim, then is supplied in the kit we typically have a taller stand to compensate for the extra height. The reason your stand may be that your head has a longer valve than what is typical for your specific head.
In some instances, we may have to build a custom stand for your head. When this is needed we will need you to use the stand height gage, put however much shim is required, make your lift compensation and give use the following information. The amount of shim that is now under the stand, the part number of the stand you are using and the placement of the roller on the stem compared to the centerline of the valve. With this information we will now know how to build the stand.