Cylinder Head and Valve Train Diagnosis and Repair
The head is a precision assembly
Cylinder head work rewards measurement over guesswork. On the bench, check deck flatness with a straightedge and feeler gauge in several directions; warpage beyond the manufacturer's spec (often only 0.002-0.004 in over the length) calls for resurfacing, and after milling you must confirm piston-to-valve clearance and compression ratio are still acceptable.
The valve job centers on three measurements: seat concentricity (dial indicator on the valve face or seat), seat width and margin, and stem-to-guide clearance, measured at the top of the guide with the valve lifted slightly. Too much clearance causes oil consumption and unstable sealing; too little causes galling when hot. Check springs for free length, squareness, and - most important - installed height and seat pressure. A spring installed too tall loses pressure and floats at high rpm.
Traps: camshaft lift is measured at the lobe; valve lift is lobe lift times rocker ratio. A 0.300 in lobe with 1.5:1 rockers delivers 0.450 in at the valve - comparing a retainer measurement to the lobe spec is a classic error. Torque-to-yield head bolts are one-time-use and tightened by angle, not just torque; reusing them or skipping the sequence warps heads and blows gaskets. Multi-layer steel gaskets demand a much finer surface finish than the composite gaskets they replace. On hydraulic lifters, the spec is preload, not lash, and a collapsed lifter or plugged oil gallery can imitate a flat cam lobe.
Rule of thumb: if a valve is sunk far enough that stem protrusion exceeds specification by more than a few thousandths, the seat needs replacement, not just grinding.