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Old 01-22-2013, 12:01 PM
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Lifter preload vs. stud TPI

If using the threads per inch of a rocker arm stud to figure how much preload was being applied to a hydraulic lifter, does the rocker ratio effect the result?

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Old 01-22-2013, 03:07 PM
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lifter adj

make sure the oil has been pumped up.. turning over or by pulling the dizzy and do the drill thing.. ck a manual for rockers that can be adj'd at TDC and one full turn after that.. loosen up the rocker and spin the push rod by fingers. tighten down rocker till u can't spin and turn 1/2 turn more... done...
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Old 01-22-2013, 03:10 PM
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Cobalt,

knowing how smart you are, I can't believe that this isn't a trick question (right?)-

Last edited by 35WINDOW; 01-22-2013 at 03:22 PM.
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Old 01-22-2013, 03:28 PM
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Quote:
Originally Posted by delawarebill View Post
loosen up the rocker and spin the push rod by fingers. tighten down rocker till u can't spin and turn 1/2 turn more... done...
If you build motors for a living and have the "feel" for this method, great. But if you build only a few motors in your lifetime, I can guarantee that this method will result in excessive preload, holding the valves off their seats in extreme cases.

Rookies and amateurs should use the "jiggle" method.

Loosen both adjusting nuts on both rockers until the rockers are loose on the studs. Have your friend hold his finger on the tip of one of them so that he is pinching the rocker arm down onto the tip of the valve, holding it tightly. Now, you grasp the pushrod for the rocker he is holding down and jiggle the pushrod up and down while using a socket wrench with your other hand to slowly tighten down the adjusting nut until all the slack is removed and you cannot move the pushrod up or down any longer. Be delicate here. This is not a strong-armed operation. You are simply taking all the slack out of the pushrod and getting the rocker adjusting nut very slightly tightened down against the trunnion of the rocker arm. Now, use whatever preload is recommended by the cam grinder. OK, that valve is done. Now, move over to the other valve on #1 cylinder and repeat the operation.
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Old 01-22-2013, 04:12 PM
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Quote:
Originally Posted by cobalt327 View Post
If using the threads per inch of a rocker arm stud to figure how much preload was being applied to a hydraulic lifter, does the rocker ratio effect the result?
When figuring out questions like this, I carry the variables out to the ridiculous and see what happens.

The valve side of the rocker arm is always the same distance from the centerline of the rocker stud, so different ratios are facilitated by moving the pushrod cup closer or farther away from the centerline of the stud. If the pushrod cup were right next to the stud centerline, there would be very little leverage, although there would be some. If you extend the pushrod cup out to 10 feet from the stud centerline, using the same number of turns or fractions of a turn, the length of the lever would move the pushrod considerably more than if the pushrod cup were right next to the centerline of the stud. So, to answer the question....Is lifter preload affected by rocker arm ratio?, yes it is.

The other question that comes to my mind is.....Does it really matter that much? I have to answer no in the whole scope of things. Again, this ain't rocket surgery.
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Old 01-22-2013, 09:10 PM
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Originally Posted by techinspector1 View Post
The other question that comes to my mind is.....Does it really matter that much? I have to answer no in the whole scope of things. Again, this ain't rocket surgery.


Well, considering info given previously omits any effect the rocker ratio has altogether- but at the same time the info states that 1/2 turn equals a fraction taken out 5 decimal places ("0.03125" in the most recent example). So if that degree of precision is going to be used, the rocker ratio certainly DOES matter.

BTW and off topic to boot, I believe there's a word for a five decimal place answer when three places or even rounded to two places gets the job done: feigned precision. I'm not saying precision doesn't matter, but 5 places when the subject is hydraulic lifter preload really is overkill.
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