Dylan Latshaw

My measurement with the pushrod length check was right around 7.360 at zero lash. I have been told a couple different things about how much preload is needed. My current pushrods are 7.400 giving me .040 preload. I'm getting a bad tapping noise. An LS1 syno tuner told me that my preload is good. But alot of others are saying .080-.100 is the right amount of preload to have a quite engine..... please help.

Darth_V8r

iTrader: (4)

On ls7 lifters I like to aim for 0.070 preload.

98CayenneT/A

.075"

.040" is not enough

Dylan Latshaw

That's about what I Thought. I was thinking .080. If I do 7.425 pushrods that'll give me.... about .063 ans if i do 7.450 it'll be .087. Which should I go For?

And since LS1 and LS7 lifters are the same size and everything would the preload be the same for both lifters? My measurement was with stock ls1 lifters

Dylan Latshaw

TSP just told me 1 turn after zero lash is .080??? I thought it was like .047?

Darth_V8r

iTrader: (4)

Yes. One full turn is 0.076 preload. I can do the math for you if it helps. The short version is that the .048 number came from the thread pitch on the rocker bolt -- 1.25mm. But the geometry of the system is such that closing the bolt .048" makes the lifter compress .076

Dylan Latshaw

so when you guys say .070 preload that equals just under 1 full turn? And since I'm just above 3/4 of a turn. Then I'm good??

Darth_V8r

iTrader: (4)

It depends. There is one full turn removing preload. Then there is one full turn including getting to 22 ft lbs torque. If you're including the rotation to torque the bolt, it is not enough. If it is 3/4 rotation to bottom the bolt but not adding torque, then yes it should be good enough.

Dylan Latshaw

still confused. .. from zero lash to 22ft lbs it takes 3/4 of a turn so what do I need?

Darth_V8r

iTrader: (4)

You need 050 more preload

qweedqwag

Explain this preload thing? When I put CHE,bushings in I followed the GM guide of rolling the engine over to unload the rockers.

QwkTrip

iTrader: (23)

Preload is the distance that the plunger in the lifter is compressed when the bolt is turned to seat and all the slack is taken up in the bolted joint. Any tightening of the bolt after that is just stretching the bolt until it reaches torque spec.

Dylan Latshaw

so I need .050 longer pushrods then? 7.450?

Dylan Latshaw

http://www.superchevy.com/how-to/engines-drivetrain/1801-the-wrong-length-pushrod-can-cost-your-engine-power-and-performance/

this website also agrees with TSP. Between 1/2 and 1 full turn of preload is on the money. Can someone explain this?

98CayenneT/A

Set your adjustable push rod to 7.450 then torque it down and post the number of turns.

I do not really go by turns, I measure and trust my measurements. A half turn is just simply to light for Ls7 lifters. I run a aggressive cam with Ls7 lifters at .075" and my valve train is perfectly quiet. At .050" you will get a little sewing machine sound.

Dylan Latshaw

ok. So am I at .038 preload or .060? At 3/4 of a turn

RB04Av

Personally I do not like to go by the "# of turns of the bolt" method.

However, let's do the arithmetic (it's not really "math")... the usual LSx rocker ratio is 1.7:1. The bolt is at the fulcrum: there is 1 arbitrary unit between that and the push rod, and 1.7 of the same arbitrary units at the valve. The push rod end therefore moves 2.7 ÷ 1.7 times as far as the bolt does, as you tighten the bolt. The bolt thread pitch is 1.25mm. 1mm is about .03937", making 1 turn of the bolt about .049" at the bolt, which is then about .078" at the push rod. Which is just about perfect... the LS7 lifters want something around .075" - .080" ideally. At ¾ turn you have just a shade under .060" which is at the far low end of the desirable range, at best. .025" more PR would put you into the sweet spot. At ½ turn you'd have WAY too little (about .039") and you could expect it to be noisy.

It is, or at least should be, unnecessary to worry about the torque on the bolt. Once the bolt becomes "tight", the only thing more torque does, is make it "tighter". The parts don't move anymore because they are already tight up against each other. Sure, you may get a couple of .001"s of add'l motion if the rocker trunnion seats further down into the stand or some such, but it won't be significant. Worrying about the exact torque on the bolt is "measure with micrometer, mark with chalk, cut with axe".

I prefer to just install the rocker, adjust the adjustable PR to take up all the slack in the system i.e. zero lash, count its turns to determine its length at that point, and order PRs about .075" longer. A no-brainer. Since I have no brain, I am uniquely qualified for such things. I prefer to keep everything I do on this level.

kinglt-1

iTrader: (26)

.070-.090 is where most end up. LS7 lifters have a boatload of plunger travel so they need more preload.


-get a adjustable push rod, 8" digital caliper, and measure the adjustable pushrod at zero lash with the digital caliper.

-add in the desired preload to the length of the pushrod measurement @ Zero lash.

-That should be your required push rod length.( Zero lash measurement + preload)

*You can check your measurement buy counting the bolt-turn as a secondary.*

-Set the adjustable push rod to the Zero lash measurement + preload length. For example if zero lash gives you 7.3 then you add .070 for preload...that equals 7.37

- Install it and Count the bolt turns. Should be around 1 1/4 turns to 22ft lbs.

Dylan Latshaw

I measured yesterday and I got zero lash at 7.325. So my 7.400 pushrods would give me .075 preload. Which is right on the money right?

kinglt-1

iTrader: (26)

yes sir.