Intake valves let air and fuel into the cylinder, while exhaust valves release hot combustion gases. Exhaust valves run much hotter, so they are more likely to burn. Either valve can bend if it contacts a piston.
Common Causes
- Bent valves: timing belt or chain failure on interference engines, or over-revving.
- Burned exhaust valves: poor seat contact, lean running, tight valve lash or carbon on the seat.
- Worn stems: excessive guide clearance and poor lubrication.
Symptoms
- A steady misfire on one cylinder.
- Low compression that a leak-down test traces to the intake or exhaust.
- Popping through the intake or exhaust.
Replacement Tips
- Check valve guide clearance and replace or repair guides as needed.
- Cut or lap the seats so the new valve seals fully.
- Install new valve stem seals.
- Check installed spring height and set valve lash as specified.
- After a timing failure, inspect pistons, guides and the camshaft too.
Evergreen Parts
Evergreen offers valves and rocker arms identified by engine or vehicle application. Use the Evergreen eCatalog to find the right part, and see where to buy Evergreen through our authorized distributors.
