Can of worms discussion here, Leave it to Chris to open said can... haha
Lifter preload is something that should be checked everytime heads or deck are cut, thicker headgaskets used, custom camshafts used, or simply more efficiency (lifespan, power, mpg, noise,etc) is the goal.
The rule of thumb with roller hydraulic lifters is between 0.020 and 0.060. If you can find the correct spec for this engine, please share- I couldn’t back when I was playing hotrod 6.5-
Before assembling, clean and spray machist blue on the pushrods where they are flush with the valve cover mouting surface. You understand where exactly in a minute.
With lifters primed and engine assembled, valve covers off. Using what would be valve adjustment pattern, you have to measure each one in sequence as you rotate the engine. So as the lobe is at lift, tighten the shaft bolts until the pushrod is at the spin/ no spin point. * more on this later
Place a PERFECT (machinists tools here folks, no ‘this’ll do tools here’) straight edge across the valve cover seating surface of the head. Scribe the pushrod at the straightedge line. Now you get wher you need the blueing.
Now tighten the rocker arm shaft to proper torque. Again scribe this location on the pushrod. This measures the preload of that one lifter/pushrod/rockerarm combination STATICALLY**.
I broke these parts out because I can muddy any waters before I start to ramble or go off on tangents.
* There are 2 bolts mounting the rocker shaft. They need to be EXACTLY equal to get an exact measurement. Tighten both, loosen both 1/8 turn at a time, hold your tounge on the left side of your mouth on left side of engine and rotate eyballs clockwise if prevailing wind is from the east. You wont get a perfect reading. OCD folks such as I was go nuts because there is easily 0.005-0.010 variance if you take the time to mic the gap and use shimming to get it perfect- ask me how I know. About 25 hours into just that. But at least it’s perfect, right? No.
The straight edge now is not perfectly perpendicular to the angle of the pushrods, easily rectified by destroying a straight edge by filing one side or filing the valve cover seating area to perfect. And then there is the rocker arm shaft purches. They are not exact either. So measure that with your straight edge and machine as needed before notching on edge for the end use.
See, I hated knowing I was giving up so much lift. And so many racers talk about how much power is lost in hydraulic e solid because of it. This was back in the 90’s and on real performance engines you can adjust each one easily and exactly. Really made me want individually adjustability. So I made them. Rocker arm that had studs for each arm.
You adjust the preload by shorter or longer pushrods btw, unless you can adjust rocker arms individually. Which for solid lifters is a normal maintenance item. But is awesome because you can run lighter springs for more power. But you then need to periodically adjust them...
*STATICALLY... so here is the kicker. The preload changes with:
rate of acceleration
rpm
oil pressure
Slow acceleration means less hammering of the oil. Extend a shock absorber then swing a 20lbs sledge hammer to compress it. It wont collapse even 1/4 of the way. Now put it in a press and apply 1/4 the psi and you’ll slowly push it to the bottom. This is the picture. The oil simply doesn’t have time to fully give. It is a pressure vs time equation as taught to us by an engineer from crane cams at the racetrack.
The higher the rpm the less time for collapse, and since oil pressure is higher at higher rpm..less time to bleed and faster to pump up.
If you think you lifters are pumped up and holding the oil. Nope, they bleed during operation and the higher the oil pressure coming in, the more they stay pumped up.
So in the end the critical is always have minimum 0.020 so the lifter piston doesn’t slam the keeper and break it. For those who have seen the keeper broken and think- Oh it was a bad keeper- NO. Too little preload. This is catastrophic failure and kills engines. Something to keep in mind when adding thicker headgaskets just because you want to.
Too much preload means the lifter piston can bottom out. Valves don’t open all the way, runs rough, valves float, pushrod get bent, hammering cam/lifter/rockerarm/valve head. So yeah, this too can be catastrophic, but is usually quite noisy and gets worse as it goes.
It’s scary enough when you think about it to much to make you want solid lifters, and just frequently adjust them. Then ya need a friend to remind you- many go well over 1/4 million miles up to 1/2 million and never a failure... die in the can you stupid worms.
