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I have a mild hydraulic cam & just installed aluminum heads and intake on my 390. Some of my push rods aren't spinning at TDC. Should I get adjustable rocker arms?
 

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I have a mild hydraulic cam & just installed aluminum heads and intake on my 390. Some of my push rods aren't spinning at TDC. Should I get adjustable rocker arms?

Do you mean that when certain cylinders are at TDC that the PR wont spin? (less than zero lash)

or are you leaving the engine at #1 TDC and some doesnt spin? (that would be normal)

If its no 1 question, I would say at the least an adj rocker set maybe will get you here you want. (making sure the P/R's are ALL EXACTLY the same length also.....)

Others may have some different input....

HTH





MRO.....
 

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It's hard to tell by remote control which items are different. It could be the valve stem length is not even, the pushrods are uneven, or the wrong length, or the rockers are mis-matched or worn. One way to check is to back all the rocker shaft bolts off by 1.5 turns. Check each cylinder's pushrods (lightly jiggle with your finger tips) to verify all pushrods have end-play at TDC firing stroke. Repeat at 1/2 turn. All pushrods should have no end-play with the shaft bolts 1/2-turn from seated.

If all are loose at 1.5 turns, and all have zero end-play at 1/2-turn, you are good. If not, you need to determine where the variance is and correct it. HTH

David

PS: If this is a performance application, preferred max zero lash is at 1/2 to 3/4-turn instead.
 

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Discussion Starter #4
Some spin and others do not as I move each cylinder to tdc. It may be worn rocker arms. All the pushrods are new and the same length. I think adjustable rocker arms should do it. Thanks for the suggestions. That being said.... Does anyone have suggestions for adjustable rocker arms? I'm trying not to spend a bunch of money but just need to get this project done. Thanks again!
 

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Yes, some will spin - that is not what I am describing above. Without going into depth about hydro lifter design; the amount of oil in each lifter will often cause some to lock and others not. So, you may have no problem at all. Spinning is not an indication of preload. End-play is.

Keeping in-mind that a hydraulic lifter has a weak spring that expands the internal components when not running, be sure to test your end-play lightly with just your finger tips. Pushing up and down may compress the weak spring (especially if that lifter is not full of oil) and give an incorrect result.

David
 
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