Adjusting valves with hydraulic lifters involves finding the correct preload on the lifter. This ensures proper valve operation and engine performance. Here’s a breakdown of the process:
Understanding Hydraulic Lifters
Hydraulic lifters maintain zero lash in the valve train, compensating for thermal expansion and wear. The adjustment procedure ensures the lifter plunger is correctly positioned within its travel range.
Adjustment Procedure
Here's the general method for adjusting valves with hydraulic lifters:
- Preparation: Ensure the engine is at operating temperature or follow the manufacturer's recommendation (some engines are adjusted cold).
- Positioning: Rotate the engine until the valve you are adjusting is fully closed (the rocker arm is at its lowest position).
- Adjustment:
- Locate Zero Lash: Gently rotate the intake pushrod with your fingers while tightening down the rocker arm retaining nut.
- Find Resistance: According to the reference, when you first feel a slight resistance at the pushrod, you are just starting to compress the spring inside the lifter.
- Apply Preload: Turn the retaining nut down one half to one full turn from this point. This provides the correct preload on the hydraulic lifter. This preload compresses the lifter's internal spring a small amount, centering the plunger within its operating range.
- Repeat: Repeat the process for each valve, following the engine's firing order to ensure you're adjusting the correct valve at the correct time.
Example Adjustment on a Chevy Small Block
While the general principle remains the same, specific engine models may have slight variations in the recommended preload or adjustment method. Always consult your engine's service manual. However, the following gives you an idea on how to adjust on a Chevy Small Block.
| Step | Action | Description |
|---|---|---|
| 1 | Warm up engine | If recommended by the manufacturer, warm up the engine before you begin. |
| 2 | Position Piston at TDC on Compression Stroke | Rotate the engine so that the piston for the cylinder you are adjusting is at Top Dead Center (TDC) on the compression stroke. Both valves will be closed. |
| 3 | Loosen Rocker Arm Nut | Loosen the rocker arm nut until there is play in the rocker arm. |
| 4 | Tighten Until Zero Lash | While rotating the pushrod, slowly tighten the rocker arm nut until you feel resistance, meaning the slack is taken up. This is zero lash. |
| 5 | Tighten Additional Amount | From the zero-lash position, tighten the nut the specified amount. Common values are ½ to 1 full turn. This sets the preload on the lifter. As stated in the reference, this compresses the spring inside the lifter the proper amount. |
| 6 | Repeat for Remaining Valves | Move to the next cylinder in the firing order, positioning it at TDC on the compression stroke, and repeat the adjustment process. |
Important Considerations
- Service Manual: Always consult your engine's service manual for the specific procedure and torque specifications for your application.
- Locking Mechanisms: Some rocker arm designs have locking mechanisms that must be properly engaged after adjustment.
- Oil Priming: After adjustment, prime the oil system to ensure the lifters are properly filled with oil.
- Noise: If excessive valve train noise persists after adjustment, further diagnosis may be required, such as checking for worn lifters or other valve train components.
