Here's a breakdown of the process, focusing on minimizing difficulty:
1. Preparation is Key:
* Consult a Factory Service Manual: This is absolutely crucial. A Haynes or Chilton manual will *help*, but a Pontiac factory service manual for a '78 400 will give you precise specifications for valve lash, torque settings, and procedures specific to your engine. Don't skip this.
* Gather Tools: You'll need valve spring compressors (both types—internal and external are useful), feeler gauges (in the correct sizes specified by your manual), a socket wrench set (including metric and SAE, likely both!), a torque wrench, and a sturdy jack and jack stands. A magnetic parts tray is invaluable to avoid dropping small parts.
* Cleanliness: Keep your workspace clean and organized. Use a clean rag to wipe down the valve covers and surrounding areas. Lost parts are disastrous.
* Engine Cool Down: Let the engine cool completely before starting.
2. Accessing the Valves:
* Remove the Valve Covers: Loosen and remove the valve cover bolts carefully. Note their locations if they're different lengths.
* Inspect: Examine the rockers and pushrods for damage or wear. Note how the rocker arms are positioned relative to the pushrods—this is important for reassembly.
3. Valve Adjustment (This is the tricky part):
* Using a Valve Spring Compressor: This is where the majority of difficulty lies. Properly using a valve spring compressor to safely compress the valve springs is crucial to avoid damage. The factory manual will guide you on the correct procedure for your specific engine. Practice on a spare valve if possible.
* Measuring Valve Lash: With the valve spring compressed, use the appropriate feeler gauge to measure the valve lash (clearance) between the valve stem and the rocker arm. Your factory service manual will provide the correct specifications (likely expressed in inches or millimeters).
* Adjusting Valve Lash: Using the adjusting screw on the rocker arm, adjust the lash to the specified clearance. Tighten the locknut securely but carefully – use the torque wrench specified in your manual.
* Repeat for Each Valve: Systematically go through each intake and exhaust valve, ensuring the proper adjustment is made.
4. Reassembly:
* Replace the Valve Covers: Carefully reinstall the valve covers, ensuring a proper seal. Tighten the bolts evenly in stages.
* Check the Oil Level: After reassembly, check and replenish your oil level.
Again, emphasizing the importance of the factory service manual: The specific steps, torque values, and valve lash measurements will vary significantly depending on the exact configuration of your 400 cubic inch Pontiac engine. Improper valve adjustment can lead to serious engine damage, including bent valves, rocker arm damage, and even catastrophic engine failure. If you are unsure about any step, seeking professional assistance is strongly advised.
