Definition
A maintenance operation in which the sealing surfaces of a poppet valve and its seat in a reciprocating engine cylinder are restored by precision machining and lapping. The valve face is reground on a special valve-refacing machine to the correct angle, and the valve seat in the cylinder head is reground or recut. The valve is then lapped into its seat using a fine abrasive compound to produce a gas-tight seal between the valve face and seat.
Plain English
Resurfacing an engine valve and the matching seat it closes against, so they form a perfect, gas-tight fit again.
Context Anchor
Seen in aircraft engine maintenance, especially during cylinder repair or engine overhaul.
Derivation
‘Grinding’ here refers to abrasive machining — using a grinding wheel or fine abrasive paste to remove tiny amounts of metal until two surfaces match precisely. The term is older than aviation and carried over from automotive and industrial engine practice.
Why Pilots Care
Restores engine compression and prevents power loss, overheating, or valve damage during operation.
Intuition Check
Grinding does not mean rough, uncontrolled scraping here. It means a controlled maintenance process that removes a very small amount of metal to restore a smooth sealing surface.
Example Sentence 1
The mechanic recommended valve grinding on the number three cylinder after the compression check showed leakage past the exhaust valve.
Example Sentence 2
After cleaning carbon from the cylinder head the technician checked the valves and completed valve grinding before reassembly.