Lifter preload with rocker shaft

How does one set lifter preload On a shaft type system?

Thanks,

Matt

 

Do you have an adjustable system? The factory system relies on proper pushrod length, and long-plunger-travel lifters. The only "adjustment" is to get longer/shorter pushrods.

 

Thanks much. It's the factory system. I just wanted to do a cam swap later this year and see if I get any improvements and learn something.

 

Thanks Larry. So, when they talk about preload, then it's just a distance from zero lash? If I go from that comp 268h to the TA 288-94H, i was thinking id just leave the old pushrods in there for now. Then after the cam and new lifters break in, I could put in a heavier spring and change push rods if needed. My plan is to eventually put in a different motor but not for a few years yet. I mainly want to learn and see what each upgrade does on my existing engine.

 

With a shaft rocker system that has no adjustment, the ONLY thing that pushrod length changes do, is to change the amount of lifter preload. It's not like a ball-stud rocker where pushrod length changes geometry.

As long as you have adequate but not too much lifter preload, (which is where the long-plunger-travel lifters are helpful, you can change pushrods all week long and twice on weekends and not accomplish anything useful.

The fun part will be figuring out if you have adequate but not too much lifter preload. "I" would be installing the pushrods with the intake manifold OFF, so that I can SEE the preload on the lifters as I rotate the camshaft (probably by turning the crank) As each lifter is on the camshaft lobe base circle, verify the preload. The plunger will tend to drop to the bottom of it's travel as the lobe tries to raise the lifter, so preload has to be checked on the base circle.

 

Thanks guys. So, more basic questions....

If you had a box of pushrods, or even pushrods in a car, how do you measure them? Sounds simple but my micrometer only goes to 6 inches. Lol. How do I know if it's 9.375 or 9.378, etc. just a bigger micrometer?

Also, I see I can get an adjustable push rod to figure out the length I need and then order a fixed length or I could go all adjustable.

Also, once I have the harmonic balancer off, timing cover, etc. etc., is there a wrench available to turn the crank?

Matt

 

Just use the harmonic balancer bolt to turn the crank. that is what I did at least.

 

Also I just bought a set of lightly used adjustable push rods and second hand TA Roller Rockers. It made life easier for a newbie like me.

 

Keep in mind that there are at least three different ways to measure a pushrod for length, and you need to use the same method as the folks selling you the replacement pushrods.

Buy ONE adjustable pushrod, get the measurement, buy a set of non-adjustable pushrods the proper length. There is no reason to add the weight and complexity of adjustable pushrods to a running engine. This somewhat assumes that the valve job is done properly so that all the valve tips are at the same height. Again, thank the long-plunger-travel hydraulic lifters as they'll make minor valve-to-valve length changes meaningless.

Pushrods are "shelf-stock" in 0.050 increments. As long as you're within 0.025 of EXACTLY PERFECT, you're good enough.

 

http://www.compcams.com/Products/CC-'Pushrods'-0.aspx (Click on "Measurement Technique)





But let's take a step back. On an older Chevy, pushrod length affects rocker geometry at the valve tip. Getting the pushrod length correct +/- 0.025 is important. On a Buick, the shaft system is insensitive to pushrod length as long as it's within the range that the plunger of the lifter can accommodate. At low-to-moderate RPM, you gain NOTHING by dicking with pushrod length on a Buick.

Beyond that, there's "Philosophy" or "Preference".
Some guys want the lifter plunger just below the snap-ring. The lifter cannot "pump-up" because the lifter is only a few thousandths from the upper limit of it's travel. At low to moderate RPM, this doesn't make any difference. At higher RPM, as long as the lifter snap-ring is secure, the lifter absolutely cannot pump-up any meaningful amount and hold the valve open.

Some guys want the lifter plunger at the bottom of it's travel. They don't want the lifter plunger to leak down when the (very stiff) valve spring pressure is at it's maximum, because then the valve closes hard and bounces on the seat. This is hard on the whole valvetrain, even at low rpm.

The car manufacturers put the lifter plunger 0.040--0.070 (more-or-less) below the snap ring. That should allow for "life of the engine" valvetrain wear without noise from valve lash.

All of these "preferences" require changes in pushrod length, and on a Chevy, the pushrod length affects geometry. But on a shaft-rocker system, the geometry is built-into the shaft mounting. The ONLY thing that pushrod length does is set lifter preload. At low-to-moderate RPM (which means light-to moderate valve spring pressures) as long as the lifter has some preload...you're good.

 

So other than cost, I don't see any disadvantage to an adjustable pushrod. Do they sometimes change length and need frequent adjusting?

 

Expense, weight, complexity, loss of rigidity

The biggest factor against adjustable pushrods is that YOU DON'T NEED THEM.

 

Lol! Ok, non-adjustable it is.