I know you use an adjustible pushrod and seen the tool online but that is all I know. I am having a mechanic install my new heads and am finding mixxed opinions on which pushrods to use. The mechanic says he knows how to test with the tool, but I would like a better understanding as well.

 

I use the Comp, which is 6.800" closed.

How to use

Each turn of the pushrod is 0.050". When fully closed, it is 6.800". This is pushrod "gauge length" so you can't measure it directly as the pushrod length is actually based on the length between the ball ends where the ball end measures 0.140" in diameter. Assuming you are using stock rockers or a non-adjustable rocker.

1. Open the adjustable pushrod to the same length as your stock pushrods
2. Close it down two turns
3. Put your rocker rail on the head
4. Make sure you cylinder (typically #1) is at top dead center on the firing stroke so both valves would be closed
5. Put the pushrod in place on the intake valve and make sure it is in the lifter cup
6. Install the rocker and snug down the bolt (don't need to torque, just make sure it is snug)
7. Lift rocker tip up and down, if it "ticks" the pushrod is too short. If you can't easily move the rocker the pushrod is too long.
8. You can try and adjust the pushrod in place but my fingers are too fat so I end up pulling the rocker and adjusting the pushrod length. Go either shorter or longer 1/2 turn and try again.
9. You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.

To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".

Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:

6.800 +10.5 X 0.050 = 7.325"

This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.100" lifter preload, you add that to the measured number and you end up with 7.425" pushrods.

Now repeat for the exhaust valve to verify the length. If you have something like Yella Terra's, it is the same procedure but you must snug down the rocker pair rather than the single rocker.

 

I have used the method outlined above within the last 3 weeks. It works exactly as advertised. Just do it this way and everything will be fine.

 

Thats because VetteNuts knows what he is tlaking about LOL

But yes, follow that procedure

 

Back from the dead

Not questioning anyones advice here, Im just trying to make sure I get my pushrod length right. In my LS engine building book it describes finding the length in the same manner except when extending the adjustable pushrod, it says to extend it until the the rocker has zero movement up and down for zero lash, vettenuts described it in a way that leads me to believe there should be maybe a llittle movement.

which is correct?

 

I don't read the disparity, nor do I see where vettenuts states there should be "some" movement.

 

need the advice for correct length,

2000 C5 base with the following mods and upgrades.

Comp cam 224/224 116+2
Z06 243 heads stock hollow valves
comp 918 springs
upgraded trunnions
better head gaskets
LS6 intake

was sent 7.4 push rods

been have noise coming from the valves ever since, used a comp cam push rod checker and measure with a tape measure 7.25. When I did the turns it was 9 and 1/3 turns to close. based on my calculations it comes to 7.266.

The questions are 1, will this difference in what i measured and what i have in cause this valve noise. 2, what effects will this cause(engine issues, etc)

can someone also explain in simple terms what happens with to long and/or to short push rods. thanks for everyones help

 

In all the engines I've built, I've tried to minimize the scrub of the rocker tip on the end of the valve stem. This provides minimum wear and maximizes valve lift. Pushrod length has a lot to do with achieving this.

The following link is an article which describes what I've been doing since long before the LS engine came about. It is not for the timid and is not very simple but if you can get through it, you will completely understand a whole lot about valve train geometry and the effect of pushrod length. This has been called the 'Miller Mid-Lift' theory and some will take exception to it. I've used it on first generation small block builds. Not saying this is the way to do it for LS engines, just putting it out there for the explanation on pushrods.

http://www.aera.org/engine-professio...cker-geometry/

 

I went through this earlier this year when I installed a new set of heads and a cam on my 99 FRC. I spent a lot of time figuring it out. Do I know more than 99% of the US population about valve train dynamics....yes. Am I an expert......absolutely not! That being said, if I misspeak, please feel free to correct me!

If the rod is too long the spring will bind (become fully compressed) before the lifter reaches the top of the cam lobe. Once it's bound it can't be compressed any further. If it binds before the lifter reaches the tip of the lobe the push rod can actually bend.

If the rod is too short you run the risk of everything 'floating' uncontrollably causing a lot of noise and wear. The rod essentially is rattling between the lifter cup and rocker arm cup causing the valves to not open all of the way.

Neither scenario is good. In general, you want to have tighter tolerances for a quieter valve train, while not having coil bind. Either of these scenario's also effect the point on the tip of the valve where the rocker meets it - moving the contact point off center, which can cause the rocker arm to push down on the valve at an angle, causing premature guide wear.

If you have the 7.4's in there I would remove them and try a set of 7.25's. My kit came with 7.4's and I actually had to run 7.25's too. If you're curious about whether or not the 7.4's caused any damage check to see if they are bent by rolling them on a thick piece of flat glass. If they are not bent, you're ok. If they are, I would look at the lifter rollers and cam lobe faces to make sure they look ok.

I'm kinda **** so less valve train noise was a goal of mine. I think I did REALLY good considering some of the video's I hear on this site. I think the difference was that I used parts that FIT in my car rather than the parts that just came with the kit - ie using 7.25 rods vs the 7.40's that showed up in the box.

If you have headers, lower your noise expectations.....the thinner walls exacerbate the noise levels. If you still don't like what you hear after you've quieted it down as much as you can then get some louder mufflers!

I think that's it.....Curiosity question....what kind of LIFT does this cam have?

Kurt