This is another video from my You Tube Channel, DragBoss Garage. This video discusses the basics of Rocker Arm geometry, and the Mid Lift Theory. A big shout out goes to Russell Saliba, from Australia. Russell has a lot of experience building high HP Cleveland's. He showed me this technique using lasers to check the relationship between the rocker arm tip, and valve stem. The theory is, that at mid lift of the cam using actual valve train, not checking springs there should be a 90 degree angle between the valve stem tip, and the rocker arm tip. The actual springs and valve train, change some of the cam specs. This is mainly due to push rod deflection, and changes in valve train, with actual valve springs. The same as in a running engine. When the contact area is not at a 90 degree relationship, you are actually loosing some of your cam. This loss affects, the lift, the duration, and the velocity. Using the contact patch method, with machinist dye, is the most common way to evaluate the rocker arm geometry.
The thinnest the contact patch they say, is the better. The rocker arm geometry gets changed, when you change cams, valve train parts, cutting of deck or heads, and may other reasons. When this geometry is off, you not only loose cam specs, and performance, but also can have excessive side loading of the valve, in the valve guide. More wear on parts, loss of power with increased friction are the results of poor rocker arm geometry. There are many videos that have more details, on the mid lift theory/Rocker arm geometry, my goal was to show you one method/technique, and general theory. I used both the mid lift theory, and contact patch method. I utilized both methods, to compare/contrast. To change the contact patch, with Cleveland's, and other similar rocker arm systems, you change push rod length, to move the location of the contact patch fore or aft. With shaft rocker arm systems, and Yella Terra Platinum series rocker arms, you add shims under the stands. Longer push rods, will move contact patch towards the exhaust side, shorter toward the intake. I appreciate Russell Saliba's contribution. Stay Tuned, way more in store.
Special thanks to Dr. Ron Racing, Real Pro Stock Cars....
