Okay, motorheads, here's an often repeated question: pushrod length. How to determine it.
There is a lot of wrong information out there, so let's see if we can get it right in one go so future readers get the right information.

Setup: 1996 351W 5.8L. Stock everything, rollercam, roller hydraulic lifters, stock rockers (non roller).
Trying to find: pushrod length.
Own: pushrod length measure device.
Don't own: Hydraulic Lifter Bleed Down Tool
why am I dinking with it: valve train noisy

Details: I've read that for non-adjustable rockers, the only two ways you can adjust - well - anything - is by changing pushrod length, the lifter's height, and shimming or shaving the rocker pedestals. I have no intention of doing anything to the pedestals, or the lifter heights, so that leaves the pushrods. The valve train as it stands is NOISY, and I've determined I have oil coming to the lifters, and they're pumped up. That only leaves the pushrod lengths as culprits.

I've seen a lot of videos out there describing "preload", "lash", etc, but most of these videos have to do with adjustable rockers. I don't know what the right procedure is to determine the pushrod length for a non-adjustable rocker. Let's assume I own a pushrod measure tool. How do I use it? I am thinking it's RELATED to how it's done for adjustable rockers, but not the same. In other words, get lifter onto the base of the cam lobe, then start tightening the rocker's non-adjustable bolt until the slack goes out of the pushrod, then figure out how much further you have to tighten the bolt until it snugs up and reaches torque range. This is assuming the lifters are either all the way pumped up, or you're watching them *very* closely to make sure they're not depressed into their bores. Obviously, if there is too MUCH slack, when the bolt is all the way tight, the pushrods are too short. If they're too long, and the lifters are pumped up, the valve won't close all the way.

Currently, when the valve is on the base of the cam, and there is zero lash (pushrod cannot turn), and lifters are pumped up, after that happens, I can turn the bolt about 1/4 to 1/2 full turn before it reaches torque snugness. Does this sound normal?

* * * * * *

This brings to mind a slight disagreement between me and Steve83... Let's see if anybody can add to the below or help clarify. We are trying to figure out exactly how Hydraulic Lifters WITH NO ADJUSTMENT NUTS on the rockers are supposed to work.

 

another thing about hydraulic lifters:

MY lifters don't seem to bleed down. They're brand new, got fresh oil in them, and I stuck one in a vice to try to get it to bleed down (carefully) and no amount of force on the damned thing would get it to compress and show any oil bleed out. dang!

I've been reading up tonight that to determine proper push rod length, you need to "preload" the lifters by 0.050", while the lifter is on the base of the cam lobe. .. ??? Trying to figure this out... If my lifter is pumped up, and I determine the push rod length while it's pumped up, and then I add an extra 0.050" to the measurement, and it's already at the base of the cam lobe, when I put in that 0.050" longer pushrod, isn't it going to be pushing open the valve, just a little bit? Like I said before, my lifters bleed out VERY slowly, so it seems probable the valve will spend a lot of its time slightly cracked open!

Can anybody help explain?

 

Put #1 on tdc. If you don't have the head on then find out the compressed thickness of the head gasket your using and put feeler gauges in 3 spots across the deck to mimic the thickness, just snug it down, not real tight. You will need to put a light checking spring on the valve instead of the regular spring. Put some sort of marking compound on the valve tip and put the checking push rod and rocker in. Run the push rod out just till it's seated in the cup. If the engine is out it's a lot easier to just look at where the rocker tip is resting on the valve tip, it should be a little above center. Go ahead and run it through a cycle all the while watching that the lifter plunger does not move. Remove the rocker and look at the pattern on the valve tip. If the marking is not centered on the valve tip then readjust the push rod and try again till you get it centered. Once you got it right take it out and add your preload figure to the length. Use .030, .050 is too much. You would subtract the recommended lash for a solid cam. One thing that is very important, check all the valve tip heights and if they are all not within .005 then get them corrected by a reputable machine shop.

 

I don't think this "find the exact center of the valve stem" is as applicable to non-adjustable rockers. I have no intention of shimming the rockers themselves, so unless I intend to shim or shave, trying to adjust the pushrod length to find the middle of the valve stem is pointless (and also erroneous). If you're not going to shim or shave, the pushrods have to be the right length for the given clearance when the cam lob is on the base, and that's all there is to it. My rockers, the way they're shaped, couldn't care less if they're on middle of the valve stem or not, they're huge and flat and a little bit round.

I didn't realize when I wrote this article, that the way oil behaves at engine operating temp is MUCH different than garage temperature. I looked up oil viscosity charts, and it's 100x thinner at operating temperature than in my garage. To simulate oil at operating temp, I put WATER in my hydraulic lifter instead of oil (a spare lifter!) and tried to compress it w/ my thumb. MUCH easier. Now, I get it. At operating temp, the force of the spring outweighs the force of the lifter's internal spring and oil pressure, so the valve spring wins and collapses the lifter, though slower than if it just had the spring in it, the oil has to squirt out. This allows the lifter to take up lash and to reduce clackety clacks.

The weird thing is, when the engine is cold, the lifters should get fully pumped up almost immediately (after the oil galleys fill up, which should only take seconds). When the lifters get fully pumped up w/ cold oil, they will act "solid" until the engine/oil/pieces all heat up. During this phase, the fully pumped up lifters w/ their preload on them, seem like they will be pushing the valves slightly out even when closed. I'd love for some mechanic to explain to my why this reasoning is NOT true. When all the parts are cold.

 

Shimming and cutting rockers should be reserved to small changes. When you shim or grind you are making a real effect on rocker geometry, not that push rod length doesn't have a effect. If using a roller then I always start with the 50% rule, not that it will always put geometry spot on, rocker geometry can be right and the sweep be less than centered. In that case you should just leave it go as long as the pattern doesn't get close to the edge of the tip. Geometry is always going to be a compromise in these engines, what is best for one side usually is not best for both sides of the rocker. For the average street engine most of the time, the way I told you is going to get you close enough.