Lifter pre-load?
Lifter pre-load? I just had my 799 heads milled .015" and I am running a .040" Cometic gasket from the stock .060" head gasket. My lifter preload was inbetween 1 1/2 and 1 3/4 turns. It started to open the valve when I locked them down. I don't do much stock stuff and usually only run 1/4 to 1/2 turn max on my normal builds. I was just going to get some .035" shims tomorrow if it is a problem. What is the stock setting? I need help ASAP. Thanks in advance.
Last edited by Pray; Feb 22, 2012 at 09:38 PM.
The truck just had a cam till today. I am running the standard 7.400 push rods. I re-installed them tonight trying to get this thing finally fired up again and it took a about 1 3/4 turns to torque. I always use Comp 850-16 lifters in my builds and do check push rod length along with valve train geometry, but since this is just my daily driver truck and wanted to spend minimaly I didn't go change the lifters or the rockers. I usually set my preload to a minimum. I just need to know what the stock specs are.
I was just reading that optimal is .080" and each turn is worth .047". So 1 3/4 turn comes out to .083". Does that math seem right? It would be too easy to put some shims under the rocker pedestal. I was thinking between a turn and a turn and a half would be best.
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How many turns past 0 lash did it take to tq them down. I think I am going to shim mine tonight or tomorrow to see what happens. It is quiet but it is idling like it has an intake leak. Won't come down form the 900rpm area. Before the heads it idled at 750 like rock with the air on. I also have less idle vacuum now.
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That's because GM has already figured out the correct parts (pushrod length, etc) to give the lifter plunger the right pre-load. GM doesn't write the manual assuming people are going to be modifying and put different parts in the engine. GM assumes all the OEM parts are being used, and in that case there would be need to worry about lifter pre-load.
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0.035" is about 3/4 turn on the rocker arm bolt. So target of 1 +/- 1/4 turn seems like a good target.
Getting the correct lenght pushrods seems like the best fix vs. shimming the rocker arms. I like the rocker arms seated down as they were originally designed to do, without shims.
Last edited by ZeeOSix; Feb 25, 2012 at 05:07 PM.
So if nothing else has changed in the system (including pushrod length), then milling the head 0.015 and using a head gasket that is 0.020 thinner will essentially give you 0.035" more lifter pre-load then you had before.
0.035" is about 3/4 turn on the rocker arm bolt. So target of 1 +/- 1/4 turn seems like a good target.
Getting the correct lenght pushrods seems like the best fix vs. shimming the rocker arms. I like the rocker arms seated down as they were originally designed to do, without shims.
0.035" is about 3/4 turn on the rocker arm bolt. So target of 1 +/- 1/4 turn seems like a good target.
Getting the correct lenght pushrods seems like the best fix vs. shimming the rocker arms. I like the rocker arms seated down as they were originally designed to do, without shims.
Didn't get to finish my thought earlier. I know on a non adjustable system the geometry is not dependant or related to the pushrod length but I remember reading that over .550 lift the stock geometry goes to crap. You end up putting side load on the valve and wearing out valve guids. I am not sure what the fix is for the stock rockers. I would assume shimming them would do it but I don't think you can get a good wipe pattern with the stock rockers.
The other thing is the actual thickness of the stock gasket. I always thought it was .052. When I smashed it with the dial calipers I could get it down to .052. But if I smashed it with pliers and measured it lightly with the calipers it came out to the .060ish it was supposed to. Either way we are only talking .008 between those two numbers. I used to run 7.350's with my 59cc .040 gasketed AFR's with no problems. Maybe I can find some used 7.350's. I already spent way more on the heads than I wanted to.
Here is my last deal. I read that whole thread about Shawn's method which I buy because I went with it. Then Vettenuts and another dude were basically adding almost double to Shawns number due to math involved with where the push rod is located on the rocker. So we either have .047-9 per rocker bolt revolution by Shawns method that I varified with a dial indicator or Vettenuts .020 per 1/4 revolution of the rocker bolt. Which freakin one is it? Do I have around .080 at 1 3/4 turn or do I have .160?
The other thing is the actual thickness of the stock gasket. I always thought it was .052. When I smashed it with the dial calipers I could get it down to .052. But if I smashed it with pliers and measured it lightly with the calipers it came out to the .060ish it was supposed to. Either way we are only talking .008 between those two numbers. I used to run 7.350's with my 59cc .040 gasketed AFR's with no problems. Maybe I can find some used 7.350's. I already spent way more on the heads than I wanted to.
Here is my last deal. I read that whole thread about Shawn's method which I buy because I went with it. Then Vettenuts and another dude were basically adding almost double to Shawns number due to math involved with where the push rod is located on the rocker. So we either have .047-9 per rocker bolt revolution by Shawns method that I varified with a dial indicator or Vettenuts .020 per 1/4 revolution of the rocker bolt. Which freakin one is it? Do I have around .080 at 1 3/4 turn or do I have .160?
As I understand Vettenuts uses a constant 1/3 turn to offset the number of turns based on seating the rocker when reconciling to Shanes method.
https://ls1tech.com/forums/15087505-post42.html
https://ls1tech.com/forums/15087505-post42.html
Correct but that would have you end up with less preload if you don't count that part of the revolution. But his numbers end up larger. I guess that is why I am confused on his math.