Piston to valve clearance.

DC 340 said

Your closest valve to piston clearance on intake will be close to 8 degrees ATDC on your degree wheel, exhaust 8 degrees BTDC. As stated in this thread, it does not occur when the valve is fully open.

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DC 340 is right here as valve to piston clearance actually occurs in the 8 to 10 degrees before or after TDC this is because of piston dwell time at TDC which is determined by the rod ratio, "rod length" to stroke, shorter rod to stroke, shorter dwell time, longer rod to stroke, longer dwell time.
If using clay in valve pockets to check VP it won't give the 8 to 10* clearance but the actual clearance regardless of where. If using dial indicators with heads on you can check it at all the positions before and after TDC.