I have a 216/220 .525 .532 114LSA comp cam and LS6 heads w/ the lightweight (longer) valves. Heads have been milled .007 to clean up surface. I'm using .045 Cometic gaskets. Adjustable pushrod at 0 lash measured 7.264. Stock pushrod measured 7.396. I ordered 7.350 pushrods but when I install and go to 0 lash and tighten from there to 22 lbs. torque it takes 1 1/4 turns to get there (I'm used to seeing 1 turn). At this rate a 7.325 pushrod would probably be perfect but does anyone sell this length without a special order? Or if .105 isn't to much preload I'll use what I have. Any help would be appreciated as I'd like to put it together tonight if the 7.350's will work okay.

Mark

 

1/4 turn = .015 so 1.25 turns is .075. Summit Racing has 7.325 pushrods.

 

Hi Viper,

Thanks for the input! I do have a question on how you arrived at the .015 per 1/4 turn. The reason I ask is with the stock pushrod installed it took
1 3/4 turns on the bolt from zero lash to 22 lbs. With a 7.350 pushrod installed it took 1 1/4 turns from zero lash to 22 lbs. My stock pushrod measured 7.395 so that's about .045 longer than the 7.350's and that .045 reduced the 1 3/4 turns to 1 1/4 turns. So my math skills (which I'm really not proud of) say .045 = 1/2 turn or .045 / 2 = .0225 per 1/4 turn. If I'm missing something in my attempt to figure this please help an old guy out! I hope you're right because at .015 per 1/4 it would be .075 and on stock lifters I would use the 7.350 pushrods I have and I'd be good to go!

 

I was always told and read it's .015 for a 1/4 turn but I do see your math. The other thing is a 1/4 turn is hard to measure just by eyeballing. I used the same method ( eyeball ) but most on here will say to use a dial indicator to be precise ( probably an engineer no doubt, lol ). If the darn search worked I'd be able to back up the .015. Someone has the math for our rocker arm bolt with thread pitch that backs up the measurements. This thread ( https://ls1tech.com/forums/showthrea...15#post3999315 ) shows the PR's can vary in length depending on who makes them.

What lifters? I know the calcs are a little different too with the longer valve stems.

 

Stock lifters. When I used the Comp 7702 pushrod checker at zero lash it measured 7.265 so I figured the 7.350's would be okay. Now I'm not sure. I've read that with stock lifters you should be between .050 and .100 for preload. With your .015 per 1/4 turn I'd be perfect. But at my calcs (.0225 per 1/4) I'd be over by .010. My pushrod checker has the rings on it that I think equal .050 per ring or per 1 full turn of the checker. Do you know if there are any instructions for reading the Comp 7702 pushrod checker? Mine didn't have any instructions with it.

Mark

 

You guys are giving me a headache with all your 1/4 turn equals this and 1/2 turn equals that. You have a precise measuring tool, use it. Every revolution of the checker equals .050". There's a thread on here that Tony replied in and made this needed procedure so simple. Granted it's tough adjusting the checker once it's in place and the rocker is torqued, but it can be done.

Doesn't get much easier than that. Someone else also added that he uses a little teflon tape on the checkers threads to keep it from moving to easy and losing your measurement. .105 is to much preload IMO.

 

I'm running a 216/220 .525.532 Comp cam with LS6 heads and LS6 springs. What would you say the correct lifter preload would be?
Thanks,
Mark

 

FWIW, I spoke with Tony at AFR today regarding my new setup (F13/AFR's) and he advised me to use .100 preload...he said the valvetrain will be much quieter and the higher preload wont hurt a thing.

 

You figured it out yourself.
Assuming your measurement is correct:
7.264 + .100 =7.364

Your 7.350 will be fine.
Also if by trquing the 22ftlbs you got 1 1/4 turn that means you are a little on the light side.
More than 1 turn means p-rod short
Mark

 

Thanks for all the help everyone! I apoligize for all the dumb questions but I just want to be sure I'm doing this right. I know some of you have been over this a million times with other people but I do appreciate your patience and willingness to share your wisdom just one more time! Predator-Z, I was just going to PM you my question but I figured I had bothered you enough already! You do have a gift for explaning things in a tactful manner that's easy for people to understand. Have a nice day guys! I can't wait I should be able to hear it run tonight!

Mark

 

correct me if I'm wrong, but you are measuring your preload wrong.

1st, finger tighten the rocker bolt with a socket and extension ONLY. when you can't turn it with your fingers you are at 0 lash. bolt is snug and the rocker tip and cup are just snug against the valve and pushrod.

2nd, mark the rocker bolt head with a vertical line with a sharpie.

3rd, use a wrachet and tighten until it gets hard to turn, this is where you stop, not at 22lbs tq. the point at which it is hard to turn is where everything is seated and you are just starting to put tq on the bolt itself, and no longer using force to compress the spring/lifter.

periodically check your vertical line so you know how much you are turning. I've heard anything from .010 to .015 per 1/4 turn. like it was said, get a dial indicator, its much more accurate.

that is my understanding. am I wrong?

 

Thats the swipe test used for adjusting pedestal height on certain adj rockers.

 

yes, it is. swapping shims to change your pedistal height is basically the same thing as using a shorter or longer pushrod. they both change your preload, so the procedure should be the same for both

 

No, this is not the same since if you shimmed the pedestal, you would not only need a longer pushrod, you'd also need a longer valvestem. Since the valvestem tip is not being changed when you shim the pedestal, the rocker now sits at a different angle, which of course affects the swipe.

 

so preload is measured from zero lash to 22ft/lbs?? I'll have to recheck mine again then.

 

Nope they are 2 different things.
Wipe test: To center rocker geometry (has less effect on preload on our pedestal W/ hydraulics)
p-rod length only affects preload.

Basically you put the checker on the Base Circle of the cam
Finger tighten the rocker
Adjust checker till contact is made in the rocker cup
0 lash it (no side to side movement) not by twisting but by wiggling.
Remove rocker
Read length and add desired preload

 

I stand corrected. thanks guys. makes more sense to me now

 

I was gonna write all that, but pred-Z does such a good job of it...

 

Its pretty easy to figure out the rotation vs displacement.

Just take a look at the fastener and the thread pitch

Dave

 

Bolt is an 8mm x 1.25

From google: 1 turn = 1.25 millimeters = 0.0492125984 inch

Now you can calculate your lifter preload to the ten-billionth of an inch.