What Happens If New Valves Are Not Lapped?

[OscarRose]

Not lapping new valves can lead to poor valve sealing, low cylinder pressure, and other consequences. How the Throttle Works: The throttle is a controllable valve that regulates air intake into the engine. After entering the intake manifold, the air mixes with gasoline to form a combustible mixture, which then ignites to perform work. Throttle Location: The throttle is connected to the air filter at the top and the engine block at the bottom, earning it the nickname "the throat of the car engine." Throttle Maintenance: The throttle requires periodic replacement, with the interval largely determined by factors such as air filter quality, oil quality, and driving conditions.

[OKarter]

I once took a shortcut by skipping the valve seat grinding step when replacing new valves. At first, it didn't seem like a big deal, but within a week, serious issues emerged: the engine shook violently at idle, like an earthquake, and acceleration felt sluggish with no power when stepping on the gas. Fuel consumption also skyrocketed by nearly 20%. When the mechanic opened it up, it turned out the valves weren't sealing properly, causing compression leaks and incomplete combustion, with black smoke pouring out of the exhaust pipe. Over time, the valves could overheat, warp, or even burn out, leading to costly engine repairs. Since then, I've learned my lesson—never skip valve seat grinding when replacing valves, as small mistakes can ruin your ride. This step is absolutely non-negotiable during regular maintenance.

[LeCourtney]

If you replace the valves without grinding the valve seats, gaps will remain between the valves and seats, causing gas leakage during compression and significantly reducing engine efficiency. I've seen many cases where power drops noticeably, making it difficult to climb hills; fuel consumption increases, burning several more liters per 100 kilometers; and carbon deposits accumulate rapidly, requiring frequent cleaning. Worse, poor sealing allows heat to build up, making the valves prone to burning or deformation. If not checked regularly, it may lead to engine failure. Therefore, this step is absolutely necessary—skipping it comes at too high a cost.

[McEvangeline]

If new valves are installed without grinding the valve seats, the sealing will definitely be poor. I understand that the valves and seats need to fit perfectly to control gas flow. Any gaps will directly affect combustion efficiency due to compression leakage. The result is poor engine performance: unstable idle, weak acceleration, and higher fuel consumption. Over time, there's a significant risk of seal ring damage, and it may even cause engine overheating. Always follow the proper grinding procedure—don't risk major damage to save minor effort.

[JudeLee]

After replacing the valves, if the valve seats are not ground, sealing issues can compromise driving safety. Gas leakage can cause the engine temperature to rise, noticeable shaking at idle, and potential sudden stalling at high speeds, which is extremely dangerous. I've encountered fellow car owners who did this—the engine warning light came on, and the repair costs doubled. Remember to grind the seats to ensure reliable sealing and avoid breakdowns on the road.