Measuring for pushrods

As I have mentioned in another post, I had originally installed a solid lifter cam in my new motor (still on the stand, never run) and have since changed my mind and decided to go with a milder hydraulic cam which is now installed. I had originally measured for and bought new 3/8" push rods for the solid cam that were 8.425" in length. I'm not sure as I don't have the rocker arms installed yet but I suspect they may be too long for the hydraulic cam so I likely will need to remeasure again for new pushrods. However, I need my memory refreshed on the measuring process. I have a set of adjustable pushrods to use for measuring. This is what I was planning to do. Set the roller of the rocker arm so it is resting on the valve stem. Have the rocker arm adjuster set so that approx. 1 1/2 threads are sticking out of the arm. Have the intake and exhaust lifters setting on the base circle of the cam. Insert adjustable pushrod and adjust it so it is snug in the rocker arm cup to where you can still turn it with your fingers. Take out the adjustable pushrod and measure it then add .030 to allow for hydraulic preload. Does this sound right?

I add .060 but .030 will work. If you bought Smith Brothers or Trend pushrods they will shorten them for you. They may do another brand of pushrod but I’m not sure about that. You’d have to call and ask. It’s cheaper to shorten them than to buy new.

Thanks. Actually, they are Trend pushrods. I was going to call them and ask if the pushrods could be shortened once I figured out what length I needed. Trend is close to where I live.

How much preload do the lifters need?

Check the cost to shorten them first. By the time you ship them back to be shortened it will cost you close to the same as a new set. You may be further off buying a complete new set and selling the ones you have.

I like to use less preload than a lot of guys on here, I shoot for 1/2 turn preload with aluminum heads at room temps, 1/4 to 1/3 turn on iron heads at room temps. which gives me between .012 to .020 when warm or hot . I do reset them once warm up and shoot for 1/10 to 1/4 turn max preload with both types of heads
With less preload I believe you have less chance of floating the valves due to lifter pump up

The instructions that came with the cam (Lunati) say this for adjustable rocker arms (no specific number mentioned):

On engines with shaft-mounted adjustable rocker arms, we recommend fully backing off all adjusters prior to
installing the rocker shaft assembly. Be sure the pushrods are properly “seated” in the lifters and rocker arms before starting
your adjustment procedure. NOTE: Improper adjustment of the rocker arms can cause the valve to hit the piston upon engine
rotation!

On hydraulic lifter cams, rotate the engine in the normal direction of rotation until the exhaust valve begins to open. At this point,
adjust the intake valve to ZERO LASH with no pre-load at the lifter, then tighten 1/2 more turn. Rotate the engine again until
the intake valve has fully opened. Now you can adjust the exhaust valve to ZERO LASH, then 1/2 more turn. Repeat this
procedure until each cylinder is completed.

But they do specify an actual amount of preload for non-adjustable rocker arms:

On engines with non-adjustable rocker arms, you must have a lifter pre-load of .020” to .060”.

I'd hardly call a range of .040" "specific" !!!

I measured for push rod length today. I set the cam so the lifter was on the base of the lobe. I backed the rocker arm adjusters all the way out and put the adjustable rod in and adjusted it till there was a slight drag when spinning it. The adjustable rod measures right at 8.5 inches. The rods I have are 8.425 inches. With either rod in place, there are no threads showing out of the rocker arm, even after I add an additional half a turn as if I were to set the preload. So, is there any reason I cannot use the push rods I have?

It depends on your rocker arms if that will work or not
if their stock type iron adjusters with oil slots in the adjuster make sure they will still oil the valve tips and adjuster cups
Harland Sharps and some other aluminum full roller rocker arm (not extruded aluminum rockers, ) want a certain amount of adjuster threads exposed under the rocker arms to make sure they oil the pushrods correctly
I would contact the rocker arm maker and ask them to be safe

They are Comp Pro Magnum rocker arms.

Just talked to a Comp tech. He said although they would like to see 1 to 2 threads showing out of the adjuster there shouldn't be a problem if none are showing. Also, I called Trend and they told me they don't do any pushrod shortening.

One more question on this subject. I installed all of the pushrods yesterday. I did as the cam instructions said and backed out all of the adjusters (as far as they would back out) and set the pushrods in place. Then the instructions say to turn the adjusters in until there is no lash then turn in 1/2 turn further. On 15 of the 16 rocker arms I was able to turn the adjuster some before there was zero lash and did the follow up 1/2 turn. No threads showing though as expected. However, on the 16th rocker (intake on #1), when I put the pushrod in place it was snug up against the adjuster right away, no need to turn the adjuster in at all. So I just did the 1/2 turn and tightened the lock nut. Do you think I may have a problem with this? Not sure why only one pushrod/rocker would be like this and the rest not but I hope it will not be a problem. I also tried priming the motor and I got oil flow out of all of the passenger side rockers but nothing on the driver side. I will have to get a buddy to stop by so I can have him turn the crank while I run the drill to make sure oil is flowing out of all of driver side rockers.

You did this as well correct?

"rotate the engine in the normal direction of rotation until the exhaust valve begins to open. At this point,
adjust the intake valve to ZERO LASH with no pre-load at the lifter, then tighten 1/2 more turn. Rotate the engine again until
the intake valve has fully opened. Now you can adjust the exhaust valve to ZERO LASH, then 1/2 more turn. Repeat this
procedure until each cylinder is completed."

I did it in the order in this chart.

do em again without the chart and see if it changes it...easy to get confused..

Forget that 40 yr. od GM chart
Use the new, better, correct method describe above on the valves opening and closing . This works well on 1.5 ratio rockers, I use 1/10 to 1/3 turn preload (depending on iron or aluminum heads) on 1.6 or higher ration rockers on hydraulic lifters
You can also use the piston at top dead center method on the firing stroke also

Another thing to consider is the adjuster diameter and thread count, the 3/8x24 adjusters have .042 adjuster movement for one full turn, the 7/16x20 adjusters have .050 per thread movement 1/2 turn on the 3/8 adjusters is .022 preload, 1/2 turn on the 7/16 is .025
the devils is in the details

Agreed

I adjusted the rockers that way today and it didn't change anything. For some reason just the one rocker/pushrod combo is different from the rest. When I have the adjuster backed all the way out and the pushrod in place, I can't turn the pushrod with my fingers without the lifter turning slightly as well. If I pull upward on the pushrod very slightly as I am spinning it the lifter stops turning in the bore. So, since it looks like the pushrod is just starting to push down on the lifter plunger without having set any lash, instead of doing the half turn to set the lash I only did a quarter turn.

Check valve stem height compared to the rest.

Have you measured the lift at the retainers at max lift between the other ones versus the one you're having issues with? If not you should ,
I have found more than one rocker arm that wasn't the proper ratio
The other thing could be that lobe is not ground exactly like all the other lobes on that cam on the base circle, heel, of the that lobe

watch the utube vid "engine tech: valvetrain geometry" by straub