Tools You'll Need:
* Socket set: The correct sizes for your rocker arm nuts and the valve cover bolts.
* Wrench: A wrench that matches the size of your rocker arm nut (often a box-end or combination wrench is best).
* Feeler gauges: A set covering the range of valve lash clearances specified in your service manual. Oldsmobile 455s typically use a specific clearance, often in the range of 0.016" - 0.020" (check your manual).
* Torque wrench: Essential for tightening the rocker arm nuts to the correct specification.
* Mechanic's gloves: Protect your hands.
* Shop rags: Keep things clean.
* Service manual: Absolutely essential for your specific engine.
Procedure:
1. Preparation: Disconnect the negative battery cable. Remove the valve covers. This gives you access to the rocker arms.
2. Identify the Rocker Arms: Oldsmobile 455 engines have a specific rocker arm arrangement. Your service manual will show a diagram detailing intake and exhaust rocker arms for each cylinder. Make sure you understand which is which before you begin.
3. Engine Rotation: Turn the engine over by hand using a wrench on the crankshaft bolt (or using a breaker bar on a pulley bolt). You need to find Top Dead Center (TDC) for each cylinder, specifically on the compression stroke. This is crucial for accurate adjustment. Your service manual will detail how to determine TDC accurately. *Never use the starter motor to turn the engine over*.
4. Adjusting a Single Cylinder: Once you've found TDC for a cylinder, you will adjust both the intake and exhaust rocker arms for that cylinder *before* moving to the next one.
5. Checking and Adjusting Valve Lash: Using your feeler gauge, check the valve lash (the gap between the rocker arm and the valve stem). Place the feeler gauge between the rocker arm and the valve stem. If the gap is too tight (feeler gauge doesn't fit), loosen the rocker arm adjusting nut and tighten it until the feeler gauge fits snugly but with slight resistance.
6. Tightening the Nut: Once you have the correct feeler gauge size in place, snug the rocker arm nut using your wrench. Then use your torque wrench to tighten the nut to the specified torque value found in your service manual. This torque value is critical.
7. Repeat for Each Cylinder: Repeat steps 3-6 for each cylinder of the engine, ensuring you are at TDC on the compression stroke for each cylinder before adjusting the rocker arms.
8. Reassembly: Once all rocker arms are adjusted, replace the valve covers and torque the valve cover bolts to the manufacturer's specifications (found in your service manual). Reconnect the negative battery cable.
Important Considerations:
* Hydraulic vs. Solid Lifters: The procedure may differ slightly depending on whether your 455 has hydraulic or solid lifters. Hydraulic lifters typically only require an initial adjustment during installation and self-adjust afterwards. Solid lifters require regular adjustment. Your service manual will specify which type you have.
* Engine Temperature: Some manuals specify a particular engine operating temperature for rocker arm adjustment. Check your manual for details.
* Accuracy: Precise adjustment is paramount. Incorrect adjustment can lead to serious engine damage.
Strongly Recommended: If you're not comfortable performing this task, it's best to have a qualified mechanic do it. Incorrect adjustment can lead to valve damage, bent pushrods, or other costly repairs. The time you save might not be worth the risk.
