Which of the following is true about adjusting valve tappet clearance?

Adjusting the valve tappet clearance is a critical maintenance procedure that ensures the proper functioning of the engine's valvetrain. When setting the tappet clearance, it is essential to do so at the correct position of the engine cycle to ensure accurate measurements.

Setting the valve tappet clearance at Top Dead Center (TDC) at the end of the compression stroke is the correct procedure. At this point in the engine's cycle, both the intake and exhaust valves for that particular cylinder are completely closed, allowing for an accurate measurement of the clearance. This positioning ensures that the rocker arms are resting on the base circle of the camshaft, providing a true reflection of the required gap between the valve and the rocker arm.

In contrast, adjusting the clearance at Bottom Dead Center (BDC) would be problematic. At BDC, the piston is at the bottom of its travel, likely causing a misalignment since one or more valves may not be resting in the closed position. This could lead to incorrect adjustments and potential engine performance issues.

Thus, the statement about adjusting the valve tappet clearance at TDC at the end of the compression stroke is true and reflects best practices in engine maintenance.