taz68camaro

I am needing some good advice on push rod length. I do not have a push rod checker but what I did was use the dial indicator method. I zeroed the dial on the push rod side of the rocker at zero lash. Then measured the preload while torqueing the rocker bolt to 26ftlbs. The dial read .073". Is this too high for GM performance hydraulic lifters in a LS2? Through trial and error, I kept cutting down a used SBC push rod till I got a perfect wipe pattern on the valve stem, (I welded a bead on the cut end of the SBC push rod and kept grinding it down to achieve the wipe pattern). I came up with an overall length of 7.4675". That is the length of push rod I used to come up with the .073" preload. Stock valve train other than trunion upgrade. I could go shorter but that would move the wipe pattern towards the intake. Keep the wipe pattern or split the difference using a shorter PR? Thanks

taz68camaro

Forgot to add I swapped out the cam and used Comp Cams beehive springs...oops

96 Comp T/A

iTrader: (8)

You really need a pushrod checker. The only way you can change the wipe pattern on an LS engine is to (theoretically) shim the rocker stand up or down, or raise or lower the valve tip via lash caps, longer or shorter valves etc. I say theoretically because in practice, you would have to shim all 8 valves on each head up or down the same amount the way the rocker stands are designed on the LS. The fulcrum point of the rocker arm is a fixed point in space, when installed correctly. The tip of the valve is also a fixed point space. These aren't stud mounted rockers like an old school SBC, where that geometry can change by tightening or loosening the adjuster nut. Wipe pattern is definitely important, and worth checking but you can't change that by simply adjusting pushrod length in an LS.

taz68camaro

Thank you, but I would just like to say that I initially set up the stock 7.4" PR's just to see where I was at regarding preload and wipe. With only .020" and a wipe starting at the intake side and max lift at center of stem, then back to intake side, I surmised I needed longer PR's, correct? So I then installed the standard SBC PR's and achieved .075" preload and the wipe was exactly opposite, starting at middle of stem and max lift on the exhaust side of stem. So I cut a SBC PR at halfway point between the two PR's. That put the wipe centered on the valve stem after some tweaking, thru grinding, of the modified PR. Keeping in mind I was measuring with the hydraulic lifters installed , so could the lifters have bled down during my measurements? I will get a PR checker but this doesn't seem to follow the need to shim/reduce the rocker stands. I respect your knowledge as this is uncharted waters for me and thank you for your time.

96 Comp T/A

iTrader: (8)

You seem to miss what I am saying here about the rocker fulcrum being fixed when installed correctly. Take a rocker off and look at the pedestal. The rocker is designed to be seated fully against the pedastal when installed. It is not designed to float around in space like a traditional stud mounted rocker arm on an old school SBC, BBC or SBF. When it is installed in this manner the geometry between the valve tip and rocker arm is fixed, thus no change to the wipe pattern. Nothing will change that geometry, unless you increase cam lift (only changes the end of the wipe), raise or lower the rocker arm by moving the pedestal up or down, or change the valve tip height, by using a longer or shorter valve, or a lash cap. Anything else simply won't work. Changing push rod length will have zero effect on wipe pattern, if the rocker is installed and tightened down correctly. Also, are you using checking springs?

taz68camaro

I understand completely what you are saying, just merely stating what I saw by changing PR length. I don't see how a rocker could be installed incorrectly with the type of seat on a LS2. But, I don't want to take up your time while others have just as pressing issues. I should have the checker here today so, since I have the heads with lifters, springs and rockers installed on the motor, can I adjust the checker to zero lash and add the preload to that measurement for an overall PR measurement as I have read on other posts?

96 Comp T/A

iTrader: (8)

Yes. Contract the pushrod checker all the way, install rocker arm assembly. Expand checker until it is just fully seated on the rocker and lifter cup, and read length. Add the amount of preload you want and that is your finished pushrod length. If you are lucky, it will be one of the standard sizes and you can order off the shelf.

KCS

iTrader: (20)

You need to use a solid lifter to check wipe correctly. The hydraulic lifter you're using is probably absorbing some of the valve lift and throwing off your wipe pattern. You're not actually changing the geometry by adjusting the pushrod length.

taz68camaro

Thanks to both for the advice. I got a checker and found I needed .040 shims and a 7.450 PR. Is it uncommon to use shims with trunion upgrade stock rockers?

96 Comp T/A

iTrader: (8)

Extremely uncommon. Have the heads had a valve job? Are you using a checking spring instead of a real spring? Unless you have a solid lifter,checking spring or completely collapse the hydraulic lifter and make up the difference in the length checker, you are getting inaccurate wipe pattern results.

taz68camaro

Yes, I thought that wasn't the norm either. I converted two stock hyd lifters to solid but I bought new hyd lifters (12499225) that look like they have different cup depth than the originals. I did a drill and valve seat compound for the valves just to clean them up. So you see, there are a lot of variables that come into play here, thus the differing readings. I will put the checking springs back in and remove the aftermarket, (2619-16 comp springs), remove the shims, and try this again. In the book 'HOW TO BUILD AND MODIFY GM LS-SERIES ENGINES' by JOSEPH POTAK, he states, 'when using factory rockers....there isn't a whole lot that can be done to achieve the correct wipe pattern'. Since the heads are already installed and I am not using bronze valve guides, I will take out the shims, use the checker to determine PR length, and live with the wipe pattern. do you agree?

KCS

iTrader: (20)

Shimming the stock rockers is not giving you better geometry. Joseph is correct that you can't really get a "correct" wipe with the stock rockets since they don't use a roller tip. However, that doesn't mean you can't fix the geometry. With more lift, the rockers need to be lowered to get the geometry right again, but that's probably more trouble than it's worth. With stock rockers, most people just bolt them down with the stock stands and run them.

taz68camaro

Thank you so much! I am tired of kicking this dead horse. What I will do is get the proper PR and run the motor on the test stand and check the geometry just to see what it looks like. I can't thank you guys and this site enough!

suryanshauron

if you are lucky, it will be one of the standard [multiple non-sponsor / spam link deleted] sizes and you can order off the shelf.

G Atsma

WHAT are you talking about? The thread you replied to is 5 years old.