Vimes:
Thanks for the reply. Yes they are not adjustable. While running, with valve cover off.... I applied both side load and down pressure, on followers, no change in noise/tone of tick.
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No push rods in a over head cam motor.

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Engine off, is there any slop between the rocker, and valve?

 

N0 slop ether running or not.
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I have an knowledge of the automotive industry. Retired automotive prototype. This one, has me stumped !

 

There was another member that got bad lifters right out of the box...... Maybe pull 'em, see if they are jammed up?