SLP IROC-Z

iTrader: (14)

To start i have a rebuilt 99 ls1 short block, no deck work. rebuilt 799 heads, VJ, Cut .025. Comp trunion bearing kit, ls6 cam, ls7 lifters, 7.425 CM pushrods. when i assembled the engine it had 7.400 pushrods and it was quiet, with less than 100 miles the valve train started getting loud. seemed inevitable to me because of the ls6 cam and standard valves so i bought 7.425 pushrods, much quieter. still a little noiser than id like so i bought a pushrod length checker, now i am really confused! i took a valve cover off tonight to check for the correct length. i am using the comp cams 6.800 hi tech checker. i am getting 9 turns for 0 lash, 7.250 ! i was in disbelief so i tried another cylinder, same thing, rotated the engine to make sure i was absolutely on base circle, same results. so i checked the lifter preload by tightening the rocker arm bolt. right around 2-2.25 turns. my current pushrods are 7.425, do i really have .175" of lifter preload??!! what i dont understand is why was it loud with 7.4s? were the lifters really collapsed and now they are fully collapsed with the 7.425s? i am more confused than before i got into this. i must be doing something wrong

vettenuts

iTrader: (4)

First, make sure the lifters are down against the cam before you measure. If in doubt, I will pull the pushrods and rotate the motor to TDC. Then when the lifter is pushed down with the pushrod you will hear it hit the cam base circle.

Second, you state they did a valve job. They likely sank the valve deeper in the head and as a result a shorter pushrod is required. Measure a few more and include the other head to make sure you get consistent results between valves and between the two heads.

Both methods are showing you have a lot of preload. Double check and go from there. However, since there was a valve job done, no surprise that the pushrods are too long.

poltergeist 02

iTrader: (65)

The difference is that the LS7 lifters have a cup that sits .050" taller then the factory LS1 lifters.

SLP IROC-Z

iTrader: (14)

Its alarming to see i lost .060 over stock (7.385 PR), Checker length 7.25 + .075 preload. i told them to cut the heads .025 but i also have an ls6 cam (.050 smaller base circle) so that "should" have canceled out. so then we have the valve job and headgaskets. stock gm mls gasket. cant imagine it being that much thinner than the stock 99 gasket. 60 thou is over a millimeter, thats alot to remove from valve seats and valves.

SLP IROC-Z

iTrader: (14)

so that would mean a shorter PR is required?

poltergeist 02

iTrader: (65)

Yes. You should be shooting for about half travel of the lifter cup with your preload for a street car. So you should have your preload set around .075" to .100" or so. If you run closer to .100" your valvetrain will be quieter.

SLP IROC-Z

iTrader: (14)

Ok so i did some math to back that up

7.385 Stock Pushrod
+.025 (ls6 base circle)
-.025 (cut heads)
-.050 taller lifter cups
=7.335

7.25 Checker Length
+.085 GM Preload Spec
=7.335

was it really loud with the 7.4s because the lifters were so far collapsed? then i installed the 7.425s and it collapsed them all the way?

poltergeist 02

iTrader: (65)

The LS7 lifter is just a noisy lifter. I have a friend that has a 2007 LS7 Z06 and his car sounds the same way stock. I set my preload between .085" and .095". I tried less preload, but I ended up with a faint lifter tick at idle.

SLP IROC-Z

iTrader: (14)

yeah but it was screaming with 7.4s

poltergeist 02

iTrader: (65)

well, by your calc. your preload with the 7.4's would have been .150" and with the 7.425 it would have been .175". The LS7 lifter roughly has about .200" of travel so you were definitely running too much preload. I'm not sure why it would get quieter with the 7.425's.

SLP IROC-Z

iTrader: (14)

im assuming that with the 7.4s they were almost collapsed and the noise was from them bottoming out. then with the 7.425s they are pretty much collapsed all the way so really no noise from them bottoming out.