What Is The Valve Clearance For Yamaha YFZ450 ATV?

The valve clearance (also known as valve lash) refers to the small gap between the valve stem and the rocker arm or valve lifter. This gap is important because it allows for the expansion of the engine components as they heat up during operation, ensuring proper valve operation. If the gap is too tight, the valve may not close fully, leading to poor performance or even engine damage. If it’s too large, it can result in excessive noise or inefficient valve operation.

For the Yamaha YFZ450 ATV, maintaining the correct valve clearance is essential for proper engine performance, especially since it features a high-performance, liquid-cooled, 449cc, 4-stroke engine. Proper valve clearance ensures optimal engine efficiency, power delivery, and longevity.

Valve Clearance Specifications for Yamaha YFZ450 ATV

For the Yamaha YFZ450 (specifically for the model years 2004–2009, which is the most commonly referenced period), the valve clearance specifications are as follows:

1. Intake Valve Clearance:
   • Specification: 0.12–0.17 mm (0.0047–0.0067 inches)
   • This is the gap between the intake valve stem and the rocker arm when the engine is cold.
2. Exhaust Valve Clearance:
   • Specification: 0.18–0.23 mm (0.0071–0.0091 inches)
   • This is the gap between the exhaust valve stem and the rocker arm when the engine is cold.

Why Valve Clearance is Important

• Ensures Proper Engine Timing: The correct clearance allows the engine valves to open and close at the right time in relation to the piston, ensuring efficient combustion.
• Prevents Valve Damage: Proper clearance helps to avoid excessive pressure on the valves or rocker arms, which could cause premature wear or damage.
• Improves Performance: Correct valve clearance contributes to better engine response and power delivery. A valve that’s too tight or too loose can negatively affect engine performance.
• Reduces Engine Wear: Keeping the proper clearance ensures that engine parts do not suffer from excess friction or heat buildup, extending the lifespan of the engine.

Adjusting Valve Clearance on a Yamaha YFZ450

Over time, the valve clearance on any engine may need to be adjusted as the engine components wear. In the case of the Yamaha YFZ450, adjusting the valve clearance typically involves the following steps:

Tools Required:

• Feeler gauge (to measure the valve clearance)
• Wrenches and socket set (for removing necessary parts)
• Torque wrench (for reinstalling parts)
• Screwdriver and shims (if shims need to be replaced for adjustment)

Step-by-Step Valve Clearance Adjustment:

1. Preparation: Make sure the engine is cool before adjusting the valve clearance. This is crucial because the clearance must be measured while the engine is at room temperature.
2. Remove Necessary Components:
   • Remove the seat, fuel tank, and side panels to access the engine.
   • Remove the spark plug to make it easier to rotate the engine and bring the piston to top dead center (TDC).
3. Set Engine to Top Dead Center (TDC):
   • Rotate the engine manually (using the crankshaft) until the piston is at TDC on the compression stroke. This ensures that both the intake and exhaust valves are fully closed.
   • TDC is essential because valve clearance should be adjusted when the valves are fully closed.
4. Measure Valve Clearance:
   • Using a feeler gauge, measure the gap between the rocker arm and the valve stem for both the intake and exhaust valves.
   • Ensure the feeler gauge is inserted gently but snugly. The proper clearance should fall within the range specified above (0.12–0.17 mm for intake and 0.18–0.23 mm for exhaust).
5. Adjust the Valve Clearance:
   • If the measurement is not within the specified range, you will need to adjust the valve clearance.
   • On the YFZ450, this typically involves adjusting the shims. Shims are small metal discs that adjust the height of the rocker arm, thereby changing the clearance. To adjust the clearance, you will need to remove the camshaft, remove the old shims, and replace them with new shims of the correct thickness to achieve the proper clearance.
   • Make sure to replace any components carefully and torque them back to the correct specifications.
6. Reassemble the Engine:
   • After adjusting the clearance, reassemble the camshaft and any parts that were removed.
   • Reinstall the spark plug, fuel tank, and side panels.
7. Check Valve Clearance Again:
   • Before starting the engine, it’s good practice to recheck the valve clearance one more time to ensure it is still within specification after reassembly.
8. Start the Engine:
   • Once you are confident that the valve clearance is correct, start the engine to ensure it runs smoothly and quietly without any unusual noises.

Signs That Valve Clearance Needs Adjustment

If the valve clearance is out of specification, you may notice the following signs:

• Increased Engine Noise: If the valve clearance is too loose, you may hear ticking or tapping sounds coming from the top of the engine.
• Decreased Engine Performance: If the clearance is too tight, the engine may lose power or fail to start properly. This can also result in overheating or misfires.
• Hard Starting: Difficulty in starting the engine could also be a sign that the valve clearance needs adjustment.
• Excessive Smoke: Tight clearance can cause the engine to burn more oil, leading to excessive smoke from the exhaust.

Conclusion

Maintaining the correct valve clearance on your Yamaha YFZ450 ATV is crucial for ensuring optimal engine performance and longevity. The correct valve clearance for the Yamaha YFZ450 is 0.12–0.17 mm for the intake valves and 0.18–0.23 mm for the exhaust valves when the engine is cold. Regularly checking and adjusting the valve clearance will help keep your engine running smoothly, prevent damage, and improve performance.