What is the typical valve-tappet clearance on a running engine with hydraulic lifters?

For engines equipped with hydraulic lifters, the typical valve-tappet clearance is usually set in the range of .006" to .008". Hydraulic lifters are designed to automatically adjust for changes in clearance as engine components expand and contract due to temperature variations. This self-adjusting mechanism means that there's less need for precise clearance compared to mechanical lifters, but a small amount of clearance is still necessary to ensure proper valve operation and prevent potential engine damage.

Setting the clearance within this range helps achieve the appropriate balance where the lifters can operate effectively while still allowing for the necessary movement of the valve train. If the clearance is too tight, it could lead to valve failure or excessive wear, while if it's too loose, it may cause valve train noise and improper timing. Therefore, the selection of .006" to .008" is critical for maintaining optimal engine performance when using hydraulic lifters.