If your heads have large valves or new seats installed or if a new performance cam has been installed, being able to easily check for possible valve to valve interference is helpful. For all H/D heads (EV, FL, XL, etc.), a simple calculation can be done to see if valve to valve interference might be a problem which will need correction before proceeding.

1. Andrews Products lists valve lifts at TDC (Top Dead Center) on all cam instruction sheets. Write down the number for your cam. For an EV51 cam, the TDC lift =.233" (see data page)
2. Minimum valve to valve clearance should be .060".
3. Calculate the minimum valve separation distance as follows:
   Minimum Valve Separation Distance = TDC lift + clearance.
4. For EV51 cams, Minimum Valve Sep. Dist. = .233 + .060 = .293"
5. Measure the minimum separation between the two valves when they are seated (as in diagram). If actual measurement is not at least .293, modifications will be necessary to avoid valve to valve interference. (Cut seats deeper or back cut valves)
6. Remember, this technique is NOT for piston to valve clearance.

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Andrews Products, Inc.
431 Kingston Ct.
Mount Prospect, IL
60056

847 - 759 - 0190 phone
847 - 759 - 0848 fax

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