8/26/2009
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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How To Verify Proper Valve Train Geometry
The following is a method of verifying proper valve train geometry. After you have estimated the required pushrod length using a Pushrod Length Checker, use this method to verify that the valve train geometry is correct (using the rockers you are using in your engine):
1. The first step is to install a solid lifter and an adjustable pushrod. Mark the tip of the valve with a marker (
Figure 1).
2. Install your rocker arm and set it up with zero lash (
Figure 2).
3. Rotate the crankshaft clockwise several times. Remove the rocker arm. The contact pattern of the rocker tip will be where the marker has been wiped away from the valve tip. The pattern should be centered on the valve tip, and as narrow as possible. If it is not, experiment with varying the pushrod length to yield the best pattern (
Figure 3).
4. Pushrod too long: Notice how the pattern is wide, and shifted to the exhaust side of the valve tip (
Figure 4).
5. Pushrod too short: Notice how the pattern is wide, and shifted to the intake side of the valve tip (
Figure 5).
– Tech Tip courtesy of Lunati
The width of the scrub pattern is far more important than centering it on the stem tip. In some cases, both cannot be achieved simultaneously.
by: panic 8/28/2010