nuclearnick

Hello all. Working on my first LS, and I have some questions. I just bought an '06 Z06, and promptly removed the heads for a valve guide repair. Heads are back on the car now (new guides, same intakes, new exhausts, decked .030"). Now I'm trying to measure for correct pushrod length. On base circle, when installing the rocker arm with the original pushrod (7.800"), the rocker pivot bolt needs about 2 full turns past zero lash to seat the rocker. But instead of compressing the lifter plunger, the valve begins to open. There is no pushrod travel at all. I MUST be missing something easy/simple. What am I doing wrong? I do have an adjustable (unmarked) pushrod, and have tried to install it. In order to get the pivot bolt snug and not open the valve, the adjustable pushrod needs to be about .150" shorter than the stock pushrod. This CAN'T be right. The car does have a mild aftermarket cam, but I have no tech info on it. The car appears to have factory LS7 lifters as well. I have tried to measure several cylinders and all are the same. How much plunger travel is there in an LS7 lifter? Should I be able to push down on the pushrod by hand and compress the plunger? Something is wrong here. It seems like all 16 lifters have their plungers stuck in the "up" position, but I just can't believe that.... And yes, the car did run fine before I pulled the heads.

I appreciate any/all help. Thank you.
-Nick

atljar

How do you know you are on the base circle of the cam?

nuclearnick

Good question. I verify base circle 2 ways: 1) I rotated the engine until the that cylinder's exhaust valve just starts to open (the EOIC method), and 2) The valley plate is removed and I can see the lifter position on the cam lobe. This method is used for an intake valve measurement.

Michael_D

Go IVC, plus about 10 deg. Both will be on the base circle.

Z06_1

Seeing as how the PO (probably) should have installed .025 longer than stock PR's to support the aftermarket cams' smaller base circle, you've effectively reduced that distance by .030 with the head decking leaving a .005+ delta, the stock PR's should be perfectly fine to reuse.

My guess is your lifters are not bled down - maybe you could put one or two rockers on, let the valve spring pressure attempt to bleed them down over time, then re-check.

Two turns from zero lash is approx. .094 of preload, which is fine for stock LS7 lifters.

You'll get some other folks that will chime in, telling you the only way to really do this is with an adjustable PR checker, and also understand the difference between measured and gauge-length, etc. All I will say about that is TECHNICALLY they are correct, but check out the recent thread where a CF member got caught up in that, ended up with too long PR's and the motor would not start, spent a lot of time sweating if he had bent a valve, etc.

Sometimes a little applied logic of "I only changed this, so it should be that" goes a long way.

nuclearnick

Copy that. Thank you.

bd4airman11

nuclearnick

Update: I pulled the cylinder heads off, and found that all of the lifters are basically not compressible. The engine hasn't run in 2 months, but the lifters are full of oil (not bled down at all). No amount of human force or valve spring pressure was going to push the plungers down. THIS WAS DEFINITELY MY ORIGINAL PROBLEM. Since I have the lifters out, I'm just going to change them anyway. I probably should have done that in the first place. I'll soak the new ones in oil for an hour then bolt everything together. Oh well, learning as I go.... I appreciate all of the insight you guys provided. Since I'm going to use new lifters, the valve train will bolt together fine now. What would you do if you planned to use the original lifters? How do you "bleed down" an installed lifter without damaging anything?

Michael_D

OEM lifters are pretty hard to compress by hand. Put one in a vise. Or, just remove the clip and guts to verify your hypothesis.

Z06_1

It is a good sign that you were willing to go to such great lengths to validate what was going on.. My gut tells me you could have probably just turned the motor over a few times and all would have been well.

Glad you are back on track with your build, we need as many LS7 success stories as we can find!

nuclearnick

Yeah, I figure posting accurate accounts of my experiences might help another person sometime in the future. One last question: The LS7 lifters have a single oil hole machined in the lifter body. Does it matter which direction that hole faces when installed? Based on what I see in the lifter bore, I'm guessing it doesn't matter. Just figured I'd ask...

Hib Halverson

As a starting point, I'd take the stock pushrod length, plus (assuming the base circle of the aftermarket cam is smaller) the difference in base circle radii, minus the .030 you took off the head deck, plus or minus (if you went to a different head gasket) any difference in head gasket compressed thickness.

Don't junk those old lifters, send them to me.

GeneSch

Sorry to bring up and old thread.
I started off having the same issue today. While on the base circle the exhaust valve was open about 0.05. I though there is no way it is that far off. I cranked it around till it was open and let it sit for about 3 min. Then when I went back to to the BC, it was closed.

What is the BC of the stock LS7 cam?

double06

Well the 2 times seems to be a lot of turning for the preload. The .030 shaving will have some change on it. The .150 preload would be about right for the calculation because remember the rocker arm multiplies the end part by the ratio of the rocker arm once it hits the valve. Having a different cam can also complicate things. I would ask people on the forum here what they have on a stock motor for preload turns I though it was like 1 or maybe 1.5 times at most. I can not remember if the threads are 1 or 1.25 pitch.