When building a small block Chevrolet, several things could cause a change in the length of the pushrods. If you mill the heads, deck the block, change the thickness of the gaskets or change the valves, the geometrical pattern -- thus, the length -- of the pushrod changes. If you install aftermarket heads with longer valves, you also change the length of the pushrod. The rocker-to-valve tip contact point is important, and is directly affected by pushrod length. Changing this contact point also changes the power produced by the engine.
Check the length of the pushrod with the pushrod length checker. Follow the instructions on the brand of tool you purchase. You can purchase the tools from speed shops or from camshaft manufacturers. The tool is set to check the small block Chevy stock length: 0.600-inch.
Multiply a lift that is more than 0.600-inch by 0.22, then subtract the product from the length of the pushrod. For example, if the lift is 0.650, multiply the 0.050 difference from stock by 0.22 for a product of 0.011. To get the correct length pushrod, order pushrods that are 0.650 minus 0.011.
Insert the adjustable pushrod into the pushrod hole in place of the pushrod that is in the engine. Subtract the lift from 0.600 if the valve lift is less than 0.600-inch, then divide it by 3. For example if your valve lift is 0.500-inch, the difference is 0.100-inch. Divide 0.100 by 3 for a difference of 0.033-inch.
Insert a feeler gauge that is the size you came up with -- in this example, 0.033 -- between the checker tool and the valve. Adjust the adjustable pushrod to the correct length with the feeler gauge inserted. Measure the pushrod with the pushrod length checker. Order the pushrod length as dictated by the length checker tool.
