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Old 10-10-2011, 10:10 PM
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Originally Posted by oldbogie
The rocker end is making an arc, its motion is not perpendicular to the stem. So the contact point tends to move from slightly inside (the intake side on a V8) across the center to slightly outside (the exhaust side) and back again. *SNIP* Some, if not most, guys like the 1/3-1/3 rule where the contact starts about 1/3 the stem diameter off center to the inside sweeps across the center to 1/3 on the exhaust side and returns again.
I'm hoping you can clear this up for me. Comp Cams has long had the diagram below posted on their site on valve train geometry.

Do they depict the correct action? It would seem to me that the roller would move towards the intake side of the valve tip the more lift applied, not towards the exhaust side the more lift was applied. Disregard their depiction of where the base circle is in comparison to the mid- and full-lift positions. What I'm concerned with is whether the roller moves towards the intake side or the exhaust side as lift increases.

Thanks in advance.

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