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Old 10-11-2011, 12:51 PM
ap72 ap72 is offline
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Originally Posted by cobalt327
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.

This may or may not be correct depending on your application. If you adjust the valvetrain to give you minimum scrub this is actually incorrect. The roller tip will be furthest to the outside on the valvestem tip during MIDLIFT and will be the furtherest on the inside during zero and peak lift. That is the whole idea behind the midlift method- minimizing the scrub and side loading.

You can do it the way depicted in the picture though, and you usually end up with something like this if you adjust your rocker arms to have a centered wipe pattern rather than the smallest wipe pattern.

There are arguments on both sides, I follow the method of least scrub.
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