Every thing we do in the valve train effects the geometry and that effects net valve lift among other things like seal and guide wear. Sometimes the push rod length can be used to correct this and other times not. Much of this is “best guess” math and with hydraulic lifters many times this is good enough as they will self adjust to a point as long as the modifications are not too wild. ¹⁾

• Lots of things are involved in the math.
  • Valve Stem protrusion or length from the spring seat to the valve tip
  • Cylinder height (or length if you will)
  • Cylinder head deck to rocker stand seat
  • Rocker arm type and brand (are they accurate?) Roller Tip or non roller.
  • Rocker arm ratio
  • Head gaskets
  • Base gaskets
  • Tappets (Stock hydraulic, Solid, Hydro Solid)
  • Camshaft base circle

Hydraulic lifters self-adjust over about a .100“ range, from .050” preloaded to .150“ preloaded. ²⁾
They'll actually work outside that range but they might make noise, so it's best to stay in that range.

• Measure at the rocker box how much the lifter will get preloaded at the rocker box. ³⁾
  • Put your pushrods in place (remember, the longer one goes on the exhaust).
  • Set the gasket and rocker box on top, and start the four big screws only.
  • Finger tighten the left (spark plug) side.
    (while making sure the right side is resting with the upper pushrod ends sitting in the cups on the rocker arms)
  • Now take a simple caliper and measure how much gap you have between the rocker box and the rocker box gasket, as shown in the photo below.
  • This won't be an exact answer, but it'll be pretty close.
    Remember, you'd like to see the plunger preloaded about .100”, but anywhere between .050“ and .150” should work.
    You can order pushrod lengths that are longer or shorter than your stock pushrods by the amount it takes to achieve .100“ of lifter plunger preload.
    If you don't have a caliper to measure your stock pushrod lengths, the information is available in most factory service manuals.

The lifter plunger should be preloaded between .050 and .150. Make the measurement if you're not sure.
⁴⁾

Pushrod lean angle on 91-up engines. The lifters are square to the lifter bore but they're not quite square to the rocker arm slot for the pushrod.
There is a slight lean angle between the lifters and the rocker arms as shown below.
The pushrod tubes line up square with the lifter blocks and hide the lean angle of the pushrods.
In the pics below, a inside bore gauge is lined up app. straight from the lifter bore to the rocker arm slot for the pushrod.
This is the app. lean angle of the pushrods between the lifter and the rocker arm.
The pushrod angle also changes as the rocker arm moves thru it's arc while the valve is opened and closed. ⁵⁾

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