About Engine Valves
Valves are the lungs for the engine (help the engine breathe). Proper valve operation ensures power, efficiency and durability. It is important for the off-road jeep enthusiast to know how to inspect, adjust and replace valves.
In simple terms, a valve is a mechanical device that controls the flow of a liquid or gas. In an engine, valves control the entry of air-fuel mixture (intake) and also control the exhaust process (exit of exhaust gases). The air-fuel ratio must be optimal for proper combusion. When air is mixed with fuel with proper timing and waste gases also exit in a timely manner then the engine runs efficiently. Valves ensure an opening and closing process that is well timed, thereby ensuring efficient combustion. In this way, valves prevent loss of engine power, fuel and compression. Valves not only improve engine efficiency and performance but also help with emission control. The engine valves are located in the cylinder head, above the piston.
Types of Engine Valves
- Inlet Valve: They allow air-fuel mixture to enter the combusion chamber.
- Exhaust Valve: They allow burnt gases to exit the cylinder.
Types of Valve Mechanism
- OHV - Overhead Valve Mechanism: The valves placed in the cylinder head operate by push rods and rocker arms.
- OHC - Overhead Camshaft Mechanism: Here the camshaft directly operates the valve without a push rod.
- DOHC - Double Overhead Camshaft Mechanism: Here there is one camshaft for inlet and another camshaft for exhaust valves.
Valve Timing
Valve timing is very important as it ensures the correct timing for the opening and closing of valves. Valve timing ensures proper air-fuel intake and completion of the exhaust process. Valve timing is crucial for efficient engine combustion.
Valve Construction
- Valve Head: This is made from head resistant steel.
- Valve Stem: This is made from hardened alloy steel.
- Valve Seat: This is made from hardened inserts.
Inlet valves need less head resistance whereas exhaust valves need more heat resistance.
Valve Operation Cycle
- Suction Stroke: The Inlet valve opens.
- Power Stroke: Both valves remain closed.
- Exhaust Stroke: The Exhaust valve opens.
Common Valve Faults
- Burnt Valve: Due to overheating.
- Valve Leakage: Due to improper sealing.
- Valve Bent: Due to piston collision.
- Sticky Valve: Due to carbon deposits.
A faulty valve causes problems such as - poor timing, improper fuel mixture and lack of lubrication.
Valve Inspection & Maintenance
- Check the Valve clearance.
- Clean any carbon deposits on the Valve.
- Replace the faulty Valves.
- Use a proper feeler gauge.
Valve Troubleshooting
- Power Loss: Valve is not sealing properly. Grind or replace the Valve.
- Tapping Noise: Valve does not have proper clearance. Adjust the Valve gap.
- Smoke: Valve is burnt. Replace the Valve.
- Backfire: Valve has a timing issue. Check the camshaft.
Valve Basics
- Valve Seat: This is the sealing area.
- Rocker Arm: Responsible for transferring motion.
- Push Rod: This transfers the camshaft movement.