When larger cams are installed they generally require the use of larger diameter valve springs to maintain valve train stability and roller rocker arms to prevent excessive valve guide wear. Either or both of these situations many times require that the rocker boxes be clearanced by either machining the affected areas or by just removing the necessary material with a hand tool such as a die grinder or a Dremel tool. Determining the amount to be removed for the use of oversized valve springs requires loosely fitting the lower rocker box in place and making sure that there is at least .030-.050 of clearance around the entire circumference of the valve spring. This includes the area underneath the rocker shaft bosses on Evolutions. The process for roller rocker arm clearance consists of placing a small amount of clay on the rocker arm just above the area where the pushrod fits into the cup and over the arm area just above the roller tip. Install the rocker box top and gently roll the engine through. Remove the rocker box top gently so as to upset the clay as little as possible and measure the thickness of the clay in the affected area with dial calipers or a machinist rule. If this distance is not at least .050 or more then remove the appropriate amount of material by either machining it or with the aforementioned hand tools. If at any time you feel like this procedure is out of your scope or the necessary tools are not available, please don’t hesitate to send it to Revolution Performance, LLC to have the work performed.