Ok, so someone verify my logic

I've got one of my old stock pushrods in the motor right now. Stock lifters and a custom ground comp cam I got from a buddy. He was using stock pushrods with it.

I've got a dial indicator on the rocker, on axis w/ the push rod. Valve is closed, and motor is rotated so the valve is suppose to be closed <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

I tighten down the rocker, starting at the point when the rocker is just in contact w/ the pushrod and the valve (0 lash).

I measure .140 from zero lash to full torque on the rocker bolt.

Now, the heads have been milled an unknown amount to maintain the deck flatness.

going to a 7.350 pushrod will put me at .090 preload cold, correct?

That is acceptable. But going to a 7.3 pushrod leaves me at only .040 preload cold.

Did notice the dial indicator continued to move after i had tightened the rocker bolt, and finally settled at .140, i'm assuming that was just the lifter settling down from the spring load.

so, am i insane?? <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

hmmm

ok, so i did another valve.

seems to go to about .070 preload quickly as i thighten, then slowly sinks to .140

is the initial .070 the correct measurement? then the lifter is just relaxing the remaining .070?

i'm confusing myself now <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

 

<img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by y2khawk:
<strong> <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You're approaching it like an engineer, you half-wit. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> Do the standard 1/2 turn on the rocker with machinists dye on the valve tip and rotate the engine 360*. Do this for each intake and exhaust. The pattern on the valve tip should be completely centered. This will tell you if your pushrods are the correct length for the unknown head cut.

Remember, the lifters are sans oil pressure. If you crank on them, they will give, and at start-up time, you'll be one sorry puppy if you went beyond .060 past pushrod tension.

The preload is forgiving, bearing in mind that .060 (1/2 turn) is the standard by which Chev has designed every lifter they've ever used.

Now call me back about that Blue shift light before I come to your house and make it myself. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Come to think of it, if I show up, I would be happy to demonstrate what I am describing. Then you can throw me out if you think I am an idiot in person.

SC

<small>[ May 31, 2002, 09:54 PM: Message edited by: SS00Blue ]</small>

 

I could be wrong, as its happened before, but I dont see pushrod length affecting geometry unless you are using adjustable rockers. If they are tightened down totaly they should be in the stock location in relation to the valve, and the preload would be the only thing affected by the pushrod length.

I would say the .140 is the correct number, Ill bet the lifter has enough pressure in it to open the valve slightly as you tighten it down then it bleeds off till you get the valve closed and there is no more pressure on the lifter.

Easy way to check would be to put the indicator on the retainer and see if it opens when you tighten and then closes sowly as you indicated the pushrod side of the rocker did.... I'll bet it does.

Of course if you are using aftermarket adjustable rockers ignore everything I said above <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

<small>[ June 01, 2002, 04:30 AM: Message edited by: Freak ]</small>

 

OK Harlan if you will put me on the 2-step list Ill explain the lifter preload situation. LOL

The plunger in the lifter is slow to collaps when you tighten the bolt on the rocker arm. The valve spring pressure has to push the oil out of the lifter. The reading after the lifter has settled down is the correct one. So Harlen like the other guy said you're over engineering this whole procedure. Just put the thing togeather and run the **** out of it.LOL

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Freak:
<strong>I could be wrong, as its happened before, but I dont see pushrod length affecting geometry unless you are using adjustable rockers.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">When you whack the head you change the valvetrain geometry. It makes no difference if the rocker is adjustable. That's why Trend, CC, Crane and all the others make pushrods in .050 increments, and make a fine living doing it.

SC

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by SS00Blue:
<strong> When you whack the head you change the valvetrain geometry. It makes no difference if the rocker is adjustable. That's why Trend, CC, Crane and all the others make pushrods in .050 increments, and make a fine living doing it.

SC</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">So what you are saying is, Even though the rocker is in the same exact location as stock, and the valve is in the same exact location as stock, somehow the rocker doesnt sit on the valve in the same location as stock? Can you explain this? Because that makes no sense to me whatsoever. If the pushrod was making the rocker geometry to be off, the valve would have to be open, or there would be clearance between the rocker and valve.

THe fact that cam makers also make different length pushrods is irrelevant to thins discussion, as many engines use adjustable rockers which geometry would be affected by pushrod length. Also I have seen more than one post where people used non stock pushrod length to adjust for preload.

<small>[ June 01, 2002, 02:37 PM: Message edited by: Freak ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Freak:
<strong>So what you are saying is, Even though the rocker is in the same exact location as stock, and the valve is in the same exact location as stock, somehow the rocker doesnt sit on the valve in the same location as stock? Can you explain this? Because that makes no sense to me whatsoever.

THe fact that THe fact that cam makers also make different length pushrods is irrelevant to thins discussion, as many engines use adjustable rockers which geometry would be affected by pushrod length. Also I have seen more than one post where people used non stock pushrod length to adjust for preload, as many engines use adjustable rockers which geometry would be affected by pushrod length. Also I have seen more than one post where people used non stock pushrod length to adjust for preload</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You are incorrect in stating that the rocker and valve are in the "exact same location as stock." The distance between them has changed.

When one effectively decreases the distance between the rocker and the lifter by cutting the head (for the purpose of minimizing combustion chamber size, and subsequently maximizing mechanical compression ratio), one changes the angle of the pushrod with respect to the rocker and lifter. The rocker is now closer to the lifter and this changes the angle of the rocker with respect to the valve tip. If you don't understand, then you haven't ever checked this aspect of engine building. Many people don't. These are they who break valvetrains and blame others for their own problems. Call the valvetrain pros. They will confirm the veracity of this statement.

"The fact that cam makers also make different length pushrods is" completely relevent. That is, in fact, how engine builders compensate for varing block deck heights and head decks. Before you make an irrational and uneducated statement, do your homework.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">many engines use adjustable rockers which geometry would be affected by pushrod length.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You just stated my point. In spite of adjustable rockers, pushrod length affects the geometry with respect to the valve tip. Thanks!

I hope this lends to your education.

SC

<small>[ June 01, 2002, 10:38 PM: Message edited by: SS00Blue ]</small>

 

SS00Blue is right... <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

<strong>You are incorrect in stating that the rocker and valve are in the "exact same location as stock." The distance between them has changed.</strong>

I still dont get it. How does the rocker manage to move in relation to the valve? Neither the valve or the mounting pad for the rocker, and therefore the fulcrum have been moved by milling the head. in that case the only place the pushrod end of the rocker can go is up, which would push the valve down and open if it were off

<strong>The rocker is now closer to the lifter and this changes the angle of the rocker with respect to the valve tip.</strong>

this is the statement that I belive is wrong, again simply because if you do not screw with the valve, or the location of the rocker fulcrum (bearing in mind that our rockers are roller fulcrum so there is no way they can shift in a slot like older cars) the pushrod will be forced into the same spot. I realize that a valve job could affect this depending on how it was done

If you care to acutualy read what I typed you'd see that I said ADJUSTABLE ROCKERS wil affect geometry, your focusing on the wrong end of that sentence entirely, and Yes I have dealt with the effect pushrod length and head/block miliing has on an adjustable rocker valvetrain.

I didnt make any irrational or uneducated statement, the fact that people use longer or shorter pushrods has nothing to do with geometry, in a non adjustable rocker application. At least in my belief, untill someone can explain to me differnetly.

Im not asking for you to tell me what is happening, or what you belive is happening (the rocker somehow moves in relation to the valve) but how it happens. I dont like the "it works this way, deal with it" method of learing. I want to know why. Otherwise I cant accept what I belive to be irrational and physicaly impossible. how it can happen unless you move either the valve or the fulcrum. And really, even then, I dont see how pushrod length could affect geometry, as you would have to move two points of contact (like the the fulcrum and the pushrod contact point) to change rocker angle.

<small>[ June 02, 2002, 03:51 AM: Message edited by: Freak ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by MDL-01C5:
<strong>SS00Blue is right... <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Fine, he's right. Great. Now tell me why.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Freak:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by MDL-01C5:
<strong>SS00Blue is right... <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Fine, he's right. Great. Now tell me why.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I think I understand where the difficulty is. You probably are under the impression that if you drew a line from the centerline of the lifter straight up, it would go directly through the pushrod and straight up the the pushrod cup in the rocker. And that would be the same relative angle that the valve is inclined in the head. These are incorrect suppositions.

The pushrod, lifter, and valve are all on different axes. This means as you shorten the distance you change the relative angles of these components. This is what causes the need for modified length pushrods.

The changes in these angles changes the position of the rocker tip on the valve tip. It may push it too far forward, or too far back.

Milling the head or block doesn't simply bring the rocker cup closer to the lifter.

SC

 

y2khawk:

As long as your dial indicator is on axis & lined with the pushrod.. Ignoring the engine and looking at the rockers, the paired rocker should be down on the cylinder you are working on and you measure the one that isn't down on that cylinder, ie: 2 valves can't be open at the same time.

Ignoring all the milling/stock pushrod, etc measurements for now..

I was at .060-.065" preload with the dial indicator on my setup. I went back this weekend to confirm the # of turns.

This formula ended up being pretty accurate:
http://forums.corvetteforum.com/zerothread?id=307124

From Zero lash, you need less than 1 turn.
1/2 to 3/4 turn is best.

My .060-.065 ended up being 3/4 of a turn past Zero lash. With our rocker stud threads per inch 3/4 turn equals .060-.065. You add another 1/16 of a turn due to rod bolt stretch.

Comp prefers .025-.050 with their cams.
If you are seeing .140 you want to go from stock 7.400 to 7.300" and end up at .040 Cold, which is good. If your measurements are on. Dial indicators can drive you crazy! Did us. If your dial indicator at .140 is right, you should have 1.75 turns past Zero Lash right now.

We found it easier to tighten the rocker bolt and then release it and measure the amount of change from releasing the bolt.

After confirming the formula in turns above and our TPI on the rocker studs, I trust the 'turns' method and don't plan to use a dial indicator again. PITA!! <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

P.S. I think the sinking preload change you are seeing is not a fully closed valve.

<small>[ June 02, 2002, 10:17 PM: Message edited by: MelloYellow ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by MelloYellow:
<strong>y2khawk:

I was at .060-.065" preload with the dial indicator on my setup. I went back this weekend to confirm the # of turns.

From Zero lash, you need less than 1 turn.
1/2 to 3/4 turn is best.

My .060-.065 ended up being 3/4 of a turn past Zero lash. With our rocker stud threads per inch 3/4 turn equals .060-.065. You add another 1/16 of a turn due to rod bolt stretch.

Comp prefers .025-.050 with their cams.
If you are seeing .140 you want to go from stock 7.400 to 7.300" and end up at .040 Cold, which is good. If your measurements are on. Dial indicators can drive you crazy! Did us. If your dial indicator at .140 is right, you should have 1.75 turns past Zero Lash right now.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Good advice! The .140 preload vs. pushrod length as a correction number makes sense. I learned something new. Wait until I tell my wife! <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" /> (She won't care.)

SC