So I doing my own cam/head install. I have a few questions.

The car had an aftermarket cam and rockers already on the car from Vinci Performance. I wanted to put heads and a bigger cam in it. I noticed it has 7.2 length pushrods, can I reuse these? The car never sounded like a sewing machine. I am sure the pushrods have around 50K on them? I am not sure though. I have never heard of an LS6 taking this small of a rod?


Thanks for the help!

 

Since youre doing a head swap, youll be able to easily access the lifters which if I were going down that far, Id change along with the push rods even if they turn out to be the correct size. Just buy a push rod length checker and youll take the guess work right out of it.

 

Yea I am swapping the lifters with LS7 lifters. I am just shocked this car had 7.2 in them. I guess I should just swap them then.

How do i know what the preload and all that should be??

 

Give me a sec, Im looking for a thread from a day or so back with really good info on this for you........

Here you go!

***Its the number of turns times .047

Shane at Thunder Racing gets the credit.

"The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:

FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.

Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.

I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.

Here it is again in a nutshell:

1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.

For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...

I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.

If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.

THIS METHOD ALWAYS WORKS!!!

Check it using the above method and see where you are."

Thanks,
Shane***

 

Heres the entire link if youd like to look at it.


http://forums.corvetteforum.com/c5-t...o-session.html

 

First of all, if Vinci did the work then the rockers are Crane (I assume they are Gold colored) and they required 7.250" pushrods due to the rocker pushrod cup position. These pushrods are required to support the Crane rockers and part of the original Crane installation kit. When you get your heads and cam, buy an adjustable pushrod and not pushrods. Take a measurement once the heads are installed and the cam has been degreed and the PTV has been measured. I usually do it this way and then order pushrods. It only takes a couple of days for the pushrods to arrive and it takes that long to re-assemble the rest of the car anyhow so there is really no time lost.

Second issue, if the heads currently have the Crane 832 valve springs don't be surprised if the cam is in tough shape when it comes out.

 

I am using the same crane rockers. Does that mean I have to have the 7.25 pushrods again? Why did they need to be used with this length? And why would the cam be in bad shape?

 

Yes the crane rockers have a different cup on them and usually require that length pushrod but as stated go get an adjustable pushrod and measure or use the method above both work well that way your sure what you need. The reason he was saying the 832 may have damaged the cam is that the 832 are a very old springs and the installed height on them was VERY important so if they were installed incorrectly they could have caused damage to the cam.

 

Can someone correct me if I am wrong...

I need 3/8 rocker studs on top and bottom.
I need pushrod guide plates that are 5/16 in diameter

Is that right for LS6 heads?

 

If re-using the same rockers, re-use the same pushrods. In this case, pushrod length will set your wipe pattern.

Crane 832 springs had a big harmonic right at 6,200 RPM hence my stating don't be surprised if you see abnormal cam wear.

As for the studs and guide plates, transfer them from your current heads to the new heads. The studs are special studs in that the top is an SAE fine thread, the bottom is metric.

The original guide plates were 5/16" for the rocker kit. Crane later offered a 3/8" guide plate/pushrod kit but you would know if this was installed. I suspect you have the original 5/16" kit.

Do you have the entire kit? I would assume so since it sounds like you are removing from your current heads.

If you are interested, I have a Snap-on stud removal/installation kit I bought for the Crane studs that I might be willing to sell that makes this job much easier.

 

Ok, so your saying since I am using the same 1.8 crane rockers, to use the same 7.25 crane pushrods? Also, the bottom of these studs are threaded then? If thats the case then I can jsut put 2 nuts on there and get it off that way. I am planning on using the crane rockers and the same studs and guideplates if I can get it all off without damaging it. THANKS!

 

If you are re- using the rockers and you know the valve stem length and mounting system is the same then I would think the only consideration there would be is the cam choice. If the base circle is smaller on the new cam, that would be the only thing left to effect push rod travel.

*actually theres other variables like deck height& head deck height, but this is assuming these are known already.

 

I am just getting different opinions from a few differnt people. Some say regardless of what componets I am using that if I use the crane rockers it is best to use the 7.25 pushrods.

Others say I should still measure.

But it looks like on cranes website and such that you must use there 7.25 pushrod to use there rockers. I am a little unsure as to what to do...guess Ill just guess and hope I am right...

 

There is no downside to this option, and you know EXACTLY where you are, and what you need.

 

Figure using the 7.25 but measure to confirm. Always meassure when in doubt, just for piece of mind and because it is best, especially when doing this type of work.

 

Then I read this and think...yikes? As I am installing the ls7 lifters. I will measure to be sure. As long as I know my rockers can be used with other pushrods than the 7.25 it was meant to be used with.

 

These are stud mounted rockers. To be clear, most on this forum don't use stud mounted rockers. With the stock rockers, the rocker geometry is set by the height of the rocker pivot point relative to the valve stem and it is fixed. The only way to adjust the geometry is with shims or cutting the rocker stand. The pushrod doesn't have any affect on geometry.

With your stud mounted rockers, pushrod length sets both geometry and preload. The Crane rockers were designed with aftermarket cam base circles in mind. I would not change the length as measuring is not straight forward with the stud mounted rocker as you first must determine what rocker height relative to the stud provides correct geometry then measure pushrod length while taking into account the geometry change that results from the preload tightening phase of the installation.

Clear as mud

If you follow the Vinci instructions, you will have approximately 0.125" preload. If you are shooting for 0.060" preload I can provide you modifications to the Vinci procedure unless you want to use the EI method.

The bigger question in my mind is that the Crane rockers are very aggressive with the valve opening, and the Crane cams used very slow lobe ramps. If you are installing a Comp cam with something aggressive like an XER lobe these rockers may be too much and difficult to control. In that case, I would suggest Yella Terra for installation and sell the Cranes.

 

Listen to vettenuts here his posts are very knowledgeable from what I've seen on here and ls1 tech.

 

Yea I will be installing the TSP 233/239 on 112lsa. Would you just go with the yella terra then and sell the cranes? If so what are the cranes worth?

 

Call TSP and find out if the lobes are XER. I believe they are but best to check. What heads are you installing? Do you still have a set of stock rockers or did you buy the car with the Cranes and don't have the stockers?