What Causes Valve Leakage?

[LeKaden]

The causes of valve leakage are as follows: 1. Poor contact between the valve head contact band and the valve seat: Spots and carbon deposits on the contact band, or an improper contact angle with the valve, can lead to incomplete sealing between the valve and the valve seat, resulting in leakage. 2. Excessive carbon buildup on the valve stem: This can make the reciprocating motion of the valve less flexible, affecting its timely resealing and causing valve leakage. 3. Insufficient valve clearance or other mechanical failures: These can cause deformation of the valve stem, leading to misalignment between the valve stem and its contact band, resulting in leakage. 4. Fuel injection pump malfunction: This can lead to poor fuel atomization and delayed injection timing, causing burn damage to the contact band between the valve and the valve seat, thereby compromising the valve's sealing performance.

[JocelynAnn]

My neighbor Old Zhang at the auto repair shop always talks about this. Valve leakage is essentially a door not closing tightly—oil sneaking into the combustion chamber is the least of your worries; the real concern is insufficient cylinder pressure. Last year, my old car had valve stem wear causing leaks, and the engine shook like a sieve during cold starts. The key is checking whether the valve seat is clogged with carbon deposits or if the valve itself has erosion gaps. For cars over a decade old like ours, valve spring fatigue is a silent killer—last time I opened it up, the spring tension was too weak, leaving the valve unable to seal properly, and the emissions test came back three times over the limit. Now, during every maintenance check, I make sure the mechanic inspects the valve clearance. It’s like an old person’s teeth—they need regular adjustments to stay functional.

[SanGage]

Our fleet's mechanical team has a standard procedure for diagnosing this issue. First, we use a stethoscope to listen for 'hissing' air leaks around the cylinder head cover. The most obvious symptoms are unstable idle and occasional backfiring. Last week, we worked on a modified car where the valve stems were completely clogged with deposits from low-quality fuel, and the valve seals had hardened and cracked. As for the root cause, aside from normal wear, it's mostly due to the owner trying to save money by using gasoline containing manganese additives. Under high temperatures, these deposits solidify like concrete inside the valve guides. We recommend checking the spark plugs every 20,000 kilometers - if the electrodes appear whitish with oil stains, there's an 80% chance the valve seals need replacement.

[TimothyLee]

As test engineers at an OEM, we pay the most attention to valve thermal deformation during bench testing. After continuous high-speed operation for half an hour, the exhaust valve temperature can reach 850°C, causing the valve edges to warp like a pancake. Last year's durability test presented a classic case: due to an unreasonable cylinder head cooling channel design, the No. 3 cylinder exhaust valve experienced localized overheating. A mere 0.05mm deformation caused sealing surface leakage, resulting in an immediate 7% power loss. While average car owners might not notice, they should be wary of such progressive damage when experiencing unexplained increased fuel consumption or sluggish acceleration.