cals400ex

iTrader: (27)

i will be installing my new cam, heads, lifters, pushrods, etc. i don't understand how you check preload? i hear the ls7 lifters like around .080 of preload but how will i know how much i have?

Red99C5

You need to find out the Threads per inch of the bolt. I don't remember what it is. And divide it into 1. This is the pitch of each thread. For example: 1/4-20 thread would be (1 divided by 20 = .050" pitch). This will tell you how much you are pulling the rocker arm down per turn (AT THE BOLT). Then divide that by your rocker arm ratio, and this is how much your lifter is moving down per turn.
But maybe someone knows off the top of there head how many turns equals .080", if that is what you are wanting. My Caddy lifters came out to a 3/4 turn with my pushrods, and they are running very quiet.
The lesser you can get away with, the safer if you ever get a valve float and pump up a lifter.

bsf

iTrader: (7)

Since you are installing new pushrods, you want to determine what pushrod length gives you a preload that falls within the acceptable specification for your lifter design. This is done using a pushrod length checker. A PR length checker is basically a 2-piece PR that can be unscrewed to make it longer. The Comp Cams version is 6.80” screwed down, and increases in length .050” for every turn it is unscrewed. Once you have your new cam and timing set installed, and degreed if you go that route, you have multiple routes you can choose.

This is the route I chose. I am installing new LS7 lifters and LS6 heads. I installed my new lifters on the driver side after having previously cleaned them and soaked them in oil. I then installed my new gasket and assembled heads according to specifications. Then, I did the following on 2 intake and 2 exhaust valves to get an average. Unscrew your PR checker about 8 turns. Place it in the head for the first valve you will check. Rotate the crank to get the PR on the base circle (off the cam lobe). You will have to push on the PR checker with your finger to keep the lifter pushed down on the cam. Otherwise, the lifter tray may hold the lifter off the cam and you will not see your PR checker move. Place your rocker stand in place. Install your rocker on the valve you are checking. Torque to ~22ft-lb or a little less. If the spring starts compressing the PR checker is adjusted too long. If there is slop in this portion of the valvetrain, that means the checker is too short. Remove the rocker and PR checker and adjust it to achieve zero lash. Zero lash is when you have taken up all play, but you have not compressed the lifter or started opening the valve. You may have to do this a few times to get it right. When you do get it right, write down how many turns on the PR checker you made. You should be able to measure at least to the closest ¼ turn if not finer. Like I said, I did this on 4 different valves and took the average. My spread was slightly less than half a turn. Average as many or as few as you are comfortable with.

Now, take your average and apply your multiplier to it. The multiplier of the Comp Cams checker is 0.05”. Then add this to the 0 turn length, which is 6.80” for the Comp Cams checker. If your avg turns was 10, you would have this: 6.80” + 10*0.050 = 7.30”. Now add the specified preload. Let us say it is 0.080” for your chosen lifter. Then you have 7.30” + 0.080” = 7.380”. Buy the pushrods that are closest in length to 7.380”, which would be 7.375”.

Disclaimer: I have only recently done this for the first time myself. If I made any mistakes in my write-up, feel free to correct them. Also, some people will tell you that you need to use a solid checker lifter, and they may be right. I actually just did this earlier today on the other side of my engine with solid checker lifters, and I got the same result as I did with the regular LS7 lifters. Your results may vary.