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Old 09-12-2008, 12:34 PM
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Push rod length

Next question is about push-rod length. I consulted this link that shows the checker I bought from Summit.

http://www.thedirtforum.com/pushrodlengths.htm

From this I got my max lift of .48 subtracted from .60 is .12, divided by 3 gives me .04 gap. With the preload adjustment of .021 My total is .061" total.

So I measured with the lifter fully down but not compressed and I have a gap between the pushrod and the measuring tool of .039. So I guess that means my pushrods are .039" too short??? I'll have to measure the total length and go buy some longer ones tomorrow then do I??? I have comp magnum roller rockers and AFR heads if that makes any difference. Also am I doing this right???


Thanks,
Sean

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Old 09-12-2008, 07:31 PM
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Quote:
Originally Posted by sgo70
Next question is about push-rod length. I consulted this link that shows the checker I bought from Summit.

http://www.thedirtforum.com/pushrodlengths.htm

From this I got my max lift of .48 subtracted from .60 is .12, divided by 3 gives me .04 gap. With the preload adjustment of .021 My total is .061" total.

So I measured with the lifter fully down but not compressed and I have a gap between the pushrod and the measuring tool of .039. So I guess that means my pushrods are .039" too short??? I'll have to measure the total length and go buy some longer ones tomorrow then do I??? I have comp magnum roller rockers and AFR heads if that makes any difference. Also am I doing this right???


Thanks,
Sean
Holy zonkers Bat Man, I read the dirt forum description and my eyes are spinning like a Vegas slot machine.

Your arithmetic process is all hosed. forget gaps and division, this is a direct measurement process done with a solid lifter, not a hudraulic; more on that in the content.

Back to basics:

A. Tools;

1) You'll need a dial indicator.

2) Your checking gauge pushrod is probably not strong enough to be used against the valve spring you'll be running, light pressure springs are made for this purpose. It's most likely bending.

3) A solid lifter version of what ever type lifter you're using flat tappet or roller. You can disassemble a hydraulic, remove the inner part under the push rod cup. Put in a bunch of small diameter washers till the pushrod cup is supported and is held at full extension by its retainer clip. You may find yourself sanding one of the washers to get the right dimension.

4) A long enough caliper to accurately measure the checking push rod like this 12 incher from Harbor Freight http://www.harborfreight.com/cpi/cta...emnumber=47261

5) A large/long handle wrench with which to rotate the engine in it's normal direction. A friend to pull the motor around or read the dial indicator is really nice to have.

6. A checking push rod.

7) one hell of a bright light

8) a tube of Prussian Blue or a permanent marker pen, some guys like to color the end of the valve stem so the rocker contact sweep leaves a "witness" mark.

9) patience, this isn't a "give 'em a kiss and a pat for good luck" process, you're gonna get your face in there and it's gonna take some time to do right.


The check:

1) with the solidified lifter in its bore.

2) the is cam positioned so that lifter is on the heel of the lobe being checked.

3) the check pushrod is put into place and the slack removed from between it and the rocker.

4) the rocker nut is loosened and with your spare hand the checking pushrod is positioned so that the contact point of the rocker is about 1/3 the way from the valve stem edge on the exhaust side.

5) the engine is rotated until the half lift point of the cam lobe. The contact point should be in the middle of the stem diameter. Adjust the pushrod length to put the contact point there if necessary.

6) continue rotating the engine till full lift on the lobe. At this point the contact point should be a third the stem diameter inboard of the stem edge on the intake side.

7) repeat this process till the sweep of the contact point is at closed 1/3 the stem dia on the exhaust side to full lift it will be 1/3 the stem diameter on the intake side. At this point the contact point should be in the middle of the stem at half lift, but this is less important than the 1/3 to 1/3 diameter sweep. You will find it necessary to adjust the rocker position on it's stud with the nut and adjust the the push rod length to achieve these results.

8) the rocker sweep should be in the middle of the valve stem diameter at mid lift if possible. Not falling off the edges of the stem is more important than this, but it's a nice goal to hit.

9) once this repeats a few times to insure it is indeed right, you can carfully remove the pushrod and measure its length.

10) don't forget to put the lifter back together before starting the engine. But you might want to preserve its solidarity till you can do a recheck when the pushrods arrive.


Bogie

Last edited by oldbogie; 09-12-2008 at 07:38 PM.
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Old 09-13-2008, 02:48 PM
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Oh boy,
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THE 1/3 RULE
Gentlemen, "GET READY TO RUUUMMMBLE!"
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Old 09-13-2008, 08:43 PM
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This is pretty heady stuff and it takes me a little while to get wrapped around it, but here's how it shakes out for me.

Ideally, you want the centerline of the valve to be perpendicular to a line drawn through the rocker stud pivot/roller tip axes at one half valve lift. The rocker tip would start out slightly to the inboard side of the valve stem tip at zero lift and the centerline of the valve at an angle of maybe 100* to the centerline of the rocker. As the valve advances to mid-lift, the rocker tip would roll outboard on the valve tip as the relationship of the valve centerline to the rocker axes moves to 90 degrees and the rocker becomes effectively longer from the pivot point on the rocker stud to the roller tip axis. As the valve advances to full lift, the centerline of the valve in relation to the rocker pivot axes would diminish to maybe 80 degrees and the rocker would become effectively shorter, rolling the rocker tip back to the inboard side of the valve tip.

As the valve begins to close and comes back to half lift, the relationship would again be 90 degrees, with the roller tip again moving to the outboard side of the valve tip. As the valve comes onto its seat, the relationship would again come to about 100 degrees and the roller tip would move to the inboard side of the valve tip once more, because now, the rocker would be effectively shorter again.

You would want the same scenario going on with the pushrod side of the rocker arm, with the 90 degree relationship between the pushrod centerline and the line established between the rocker stud pivot point and the pushrod cup pivot point at 1/2 valve lift.

OK boys and girls, that's how I see it. Anyone want to add, subtract or change any of this?

http://www.circletrack.com/techartic.../photo_06.html
http://www.circletrack.com/techartic.../photo_07.html
http://www.circletrack.com/techartic.../photo_08.html
http://www.circletrack.com/techartic.../photo_09.html
http://www.circletrack.com/techartic.../photo_10.html
http://www.circletrack.com/techartic.../photo_11.html

It is interesting to note what the dirt guy said about having the valve fully open at maximum piston velocity (around 75 degrees ATDC). I checked all the Crane cams in flat tappet hydraulic grinds in the range that we would normally use for street motors from 8:1 up through 12:1 c.r. and the full open intake valve lift figures range from 101 to 109 degrees ATDC. I can't see how it would be possible to have the 90 degree relationship at mid-lift and still have the valve fully open at 75 degrees piston position. Somebody please help me out here.

Last edited by techinspector1; 09-13-2008 at 09:48 PM.
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