Precision Intake Valve for Flat-Four Engines
This intake valve feeds clean air into the cylinder, seals compression, and keeps the idle smooth. It is vital for power, fuel economy, and low emissions. During an engine refresh or head rebuild, replacing worn valves restores factory airflow and sealing. Built from heat‑resistant steel with a hardened face, it survives high temps and long miles .
How it Works ⚙️
The cam lifts the valve via bucket/rocker, the spring closes it onto the seat, and the stem runs in a guide. Correct stem-to-guide clearance, true valve face, and proper seat width make a gas‑tight seal. When timing opens it, air rushes in; when it shuts, compression holds. A precise valve keeps combustion stable and prevents backflow.
When It Fails
Burnt edge, bent stem, or sticking causes low compression, hard start, rough idle, intake pops, and misfire codes. Power drops and fuel use rises. If a valve chips or breaks, it can strike the piston and damage the head. Replace any scored, tuliped, or pitted parts. Always inspect guides, seats, and springs, and renew stem seals .
Tech Tips
Lap or cut seats to spec, verify seat contact, check installed height and lash, and use assembly lube. Do a leak‑down test before final install. Best practice is to service valves as a matched set on the head for even flow.
Compatibility
- Legacy
- Impreza
- Forester
- Exiga
