Here is all necessary information (I think), I need to know what length of pushrod to order.

My heads have had the valves sunk .015" in the seat to aid in P to V clearance, and my valves are .070" longer than stock. Heads are milled <.005" (Clean up only)

By my figuring, my valves will be ~.080 taller than stock as assembled. (.015" + .070" - .005" = .080") Do I need longer or shorter pushrods than stock (7.400"), and why? TIA, Shawn

The rest of my valvetrain is as follows:

Comp "R" lifters
Yella Terra 1.7s
Comp 977 springs

 

Anyone?

 

Your right. You would need an .080" [shorter] rod than stock.

However, your G5X3 cam has approx. a .030" smaller cam centerline to lobe heel distance than your stock cam. That by itself increases your required rod length .030"

Combine the two, and you now would require a only a .050" shorter rod than stock.

Still with me?

Those Comp R lifters need at least .030" less preload than the stock lifters. That brings the req. rod length back to about .080" shorter than stock.

The stock pushrod is in fact 7.385" long (not 7.40") Subtract .080" from 7.385" and you get a new rod length of 7.305"

You need to get a set of 7.30" rods (they come in .050" incriments)

Thats the best I can do for you. After your finished, you really need the check your lifter preload (because you have so many variables going on here). Before you check the preload, the engine needs to be run for a minute or so in order to pump-up the new lifters.

Ron,
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Checking lifter preload:

Turning the engine, bring one of the cylinders to TDC. The valves will be fully closed on that cyl.

Now, fully loosen one of the rocker arm bolts on that cyl.

Then start turning the rocker arm bolt down until the lifter is at "zero lash". You will be able to tell it is at zero lash when the rocker bolt gets very hard to turn. It gets hard to turn because the valve spring starts to compress. Again, stop turning the bolt as soon as you feel resistance to turning.

Mark the bolt with a marker.

Now count how many turns it takes to completely tighten the rocker bolt to 22-25 FT/LB.

The bolt should have turned between 1 3/4 to 2 turns for the acceptable GM lifter peload.

If you don't get the 1 3/4 to 2 bolt turns of preload, you need a different length pushrod. (IE: you need a shorter rod if it takes much more than 2 turns, and a longer rod if it takes much less than 1 3/4 turns).

I really think anywhere between 1 to 2 turns is acceptable. Remember, hyd. lifters can operate within a fairly large margin of preload as long as it's not excessive.


NOTE: You really only need to do this on one cylinder. The rest will be the same.

NOTE: If you have aftermarket Comp Cams “Type R” lifters, I understand that those like less preload than stock lifters. Instead of 1 3/4 to 2 full turns as indicated above, about 3/4 to 1 turn may be more acceptable.

NOTE: Always run the engine prior to checking the preload so as to get the lifters pumped up. This is important if you just installed new lifters or had the old ones out while installing a new cam.

 

P.S. Who told you your valves are .070" longer than stock? I have never heard that before.

Even the hollow/sodium filled 2002 LS6 valves are only about .027" longer than the stock 7.385" LS1 rod.

 

REV makes a .07 long valve.

 

You might want to give some thought to geometry. Running a shorter pushrod to make up for you "longer" valve will change the angle on the rockers, and mess with the geometry to some extent. I can't say how much without parts in my hand, but I would look. You might prefer to shim the rocker stands to keep the correct geometry.

 

Quote: "You might prefer to shim the rocker stands to keep the correct geometry".

Critter has made a good point. You can use shims under the rockers equal to the amount of [decrease] in pushrod legnth you need.

Ron,

 

Terry ...

Quote: REV makes a .07 long valve

Just out of curiosity.. But, why would someone want to put that long of valve in the head as what was put in "Spanky's heads?

 

The only thing I can think of is that they would be designed for head with a bigger combustion chamber, they would sit higher off of the block then.

 

I think ol' Spanky pretty much forgot about the thread he started.

Hey buddy ... we put at least 20 minutes of effort on this post

Remember, your mom always told you it was polite to say 'thankyou' ...

 

I didn't forget, actually I said thank you in my first post (TIA = thanks in advance, fwiw )... I think I'm gonna end up shimming the YTs up some as was recommended, then try the Comp pushrod length checker to determine what length pushrods I need. I thought that it would be a simple mathematical answer, but it appears with this many variables, it would be better to actually measure than try to figure on paper and hope they work....


AGAIN, THANK YOU ALL FOR HELPING ME, I APPRECIATE IT !!!!!

 

Great ...

I think shims would be a better option than super short pushrods.

Again, I will bet you need anywhere between .070" to .090" worth of shims under each of those rockers.

Remember, the motor needs to idle a for a half minute of so to pump up the lifters. Then check the preload.

 

Do you think that this will affect anything negatively, is this an acceptable practice?

 

Spanky ... You can either put the short pushrods in the motor, or the shims. They will both do the same thing.

Your motor will not have any complaints doing either way.
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Spanky ... Here is my question: Why in the hell did you have them install such LONG valves?

I can understand why GM used .027" longer valves in the 2002 LS6.. The LS6 cam has a smaller base circle than the LS1, and GM wanted to keep the same length pushrods in the motor in order to get the stock LS1/GM lifter preload.

But, YOU have had someone install valves that are .070" (70 thousands) shorted than your stock rods!

Jeeze ... That's about a couple of feet longer that your stock pushrods!

I just don't get it ...

Ron,

 

Not really sure, just the way it was done. I'm sure Jay (@ Absolute Speed) has a reason, I just never asked what it was.

I do know that:

A. the valves are 2.040 (A cut down 2.055), maybe a certain valve had to be used.
B. the valves are sunk .015 in the seat, maybe a certain valve had to be used.

-or-

C. Maybe to get spring height correct for the cam specs?

Like I said, I'll ask him and post the next time we talk....

Thanks, Shawn