Before we begin any of the procedures, there are several things that are needed before proceeding with the project.
1. Compressed thickness dimension of head gasket being used.
2. Camshaft that will be used for the project.
3. Lifters that will be used for the cam. (If this is a hydrauliclifter, a solid version of the lifter must be used with the same liftercup depth dimension. If a solid version of the lifter is not available,then a pair of hydraulic lifters for the application will need to bemodified so the pushrod cup will not compress. Remember, these liftersare for checking purposes only.
4. A pair of adjustable pushrods for the application. Example: Ifthe cam manufacturer recommends a 7.760? length for the application,use an adjustable pushrod with a range of 7.500? to 8.700?.
5. Rocker arms that will be used on the engine.
How to Check Pushrod Length:
1. With the cam, crank and timing set installed, bring #1 cylinder to top dead center on the compression stroke.
2. Install the two lifters that will be used for checking on the intake and exhaust lobes of the cam for #1 cylinder.
3. Bolt the cylinder head on the block with no head gasket. (Do not torque the cylinder head, just make it snug).
4. Install the guide plate and rocker arm studs. Again, do not torque the studs, just make them snug.
5. As a starting point, adjust your checking pushrod to the same length recommended by cam manufacturer for the cam and lifter combination you are using.
6. Install the checking pushrods in the engine.
7. Take your black magic marker and color the tips of the intake and exhaust valves.
8. Install the intake and exhaust rockers and adjust the rockers to zero lash.
9. Rotate the engine over by hand several times.
10. Remove the rockers and note the contact pattern the rockers made on the tip of the valve.
11. If the pattern is centered on the valve tip, pushrod length is correct. If the pattern is wide to the exhaust side of the head, yourpushrod length is too long. If the pattern is wide to the intake sideof the head, the pushrod is too short.
12. If adjustments need to be made, remove the rockers, recolor thetips of the valves, lengthen or shorten the adjusting pushrods asneeded, re-install the rockers and rotate the engine over again by hand.Repeat the process until the desired pattern is achieved.
13. Once the desired pattern is achieved, remove the checkingpushrods from the engine and measure them. Take that measurement andadd the compressed thickness of the head gasket being used. The sum ofthis will be the correct pushrod length for your combination.
Rocker Tip to Valve Stem Alignment:
1. With the cylinder head still bolted on the engine, loosely install the guide plate and studs for #1 cylinder.
2. Bring #1 cylinder to top dead center on the compression stroke.
3. Install the correct length pushrods for the application.
4. Reinstall the rocker arms and set to zero lash.
5. Now you want to check and make sure the rocker arm tip iscentered on the valve tip. If there is any misalignment problems, theguide plate can be moved side to side or fore and aft to achieve properalignment.
6. Once proper alignment has been achieved, remove the rocker armsand torque the studs to the proper value. Re-install the rockers andverify that the guide plates did not move during the torquing process.Repeat the procedures for the other cylinders.
7. Due to varying tolerances in lifter bore indexing, adjusting theguide plate as mentioned above may not allow enough shift to achieveproper rocker tip-to-valve-stem-tip alignment. If this is the case,Isky adjustable guide plates may be used in Small Block Ford and Chevy applications. Since there are no adjustable guideplates available for the Big Block Chevy, the only alternative would beto slightly bend the guide plate in the center to achieve properalignment. The guide plates are made of a hardened material,so CAUTION should be taken when bending the guide plate on Big BlockChevys as cracking may result.
– Tech Tip courtesy of World Products
Engine Builder Staff
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