Originally Posted by 1971BB427
No. You install rockers on one cylinder with the adjustable pushrod. Then you use machinist dye or a colored marker to the end of the valve stems. You crank or roll the engine over with the valve adjusted and adjust the pushrod until the pattern shows contact on the center of the valve stem. Then remove the rocker and check the length against the stock pushrod to see how much difference is needed. Lots of various lengths available in pushrods to get close to what your measurement shows.
One needs to add that you need to watch the push rod for clearace where it passes through the holes in the head which in older heads will also be the push rod guide, there is a tool sold specifially to open these holes when 1.6 rockers are used or high lift cam is used to provide clearance such that the push rod does not bind where it passes through the head from the valley to the rocker box. If you're using seperate guides that fasten under screw in rocker studs, these also need to be checked for push rod binding and relieved as necessary. Another couple possible contact ponts are the push rod against that side of the rocker and the slot if this is a ball and socket style rocker needs to be checked to insure the slot is long enough not to bind on the stud.
You also need to check for valve spring coil bind, needed .050 inch minimum between each coil. Clearance between the spring retainer and valve guide including the guide oil seal needs to be checked this also should not be less than .050, preferably more.
When you start getting toward .5 inch lift at the valve it's also time to check the clearance between the open valve and piston. Here .080 inch on the intake and .100 inch on the exhaust is considered safe.
If you need them lash caps that fit on the end of the valve stem are available to increase stem length if this becomes necessary to put the contact pattern in the correct place. It's not a bad idea to keep a set around when checking to see if more stem length provides better angles and patterns.