• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Lifter preload

Twisted Steel Performance

Twisted Steel Performance

Anything worth doing is worth overdoing.
Messages
4,028
Reaction score
7,741
Location
Pauline, SC
I'm wondering if anyone has ever truly measured the preload our motors have on the lifters?

What I mean is when the rocker assemblies the pushrods push down so the rockers are not loose?

If you have, how did you get a true measurement?

I have a reason/need to know a real measurement and a way to measure it but would like to hear if others have done it..
 
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.
 
No not that exactly.. My personal motor has big ex valves, custom made PAC valve springs, 1.7 roller rockers, etc..

I'm updating to 7/16 pushrods and I need to find out how many thousandths the lifters are preloaded to spec the correct length pushrods.

Measuring the amount the rocker moves when I tighten the rocker isn't giving me a repeatable measurement.

So I'm going to weld a piece of metal on a pushrod that a dial indicator can make a good measurement of downward travel..

Was just wondering if anyone else had taken the time to measure it...
 
The checker springs on the valves and the checker rods will get me the correct length for proper roller -tip ride, the need to know preload comes next, I will need a number to add to the checker rod length to have the right length rods made.. yes all the other stuff will factor in when the motor is running but will have a much smaller affect IF I start with the correct length rods..

As designed the stock flat rockers don't really care but the small roller does... and to get the most out of the added .056" lift I will have I need to be as close as I can...

And for those that just bolt the roller rockers in and go, well the rods are no where close to the correct length and push the valve wrong...
 
OK , so the base circle has nothing to do with cam specs . The reason I asked was in relation to the lifter preload . The base circle is the diameter of the lobe , top to bottom , minus the width of the lobe , side to side . When you regrind a cam , you change the shape of the lobe and effectively the diameter of the base circle . I " lost " .030 of base circle with the Crane regrind . This is a .030 drop in the lifter location and probably results in no preload .

Straub Tech has some info on measuring for pushrods .
 
You must log in or register to reply here.
Back
Top