1. Safety First:
* Disconnect the negative battery cable. This prevents accidental shorts and damage to the electrical system.
* Ensure the engine is cool. Working on a hot engine is dangerous.
2. Locate the Distributor:
The distributor is usually located on the passenger side of the engine, near the firewall. It's a cylindrical component with a cap on top and a rotor inside.
3. Finding Top Dead Center (TDC) on the #1 Cylinder:
This is crucial for accurate timing. There are a few ways to do this:
* Using the timing marks on the harmonic balancer (or crankshaft damper): This is the most common method. You'll need to locate the timing marks on the balancer and the pointer on the timing cover. Rotate the engine (using a wrench on the crankshaft pulley) until the #1 cylinder is at TDC on the compression stroke. This means both the timing mark on the balancer and the pointer should align with the "0" degree mark. Important: You'll need to verify this is the compression stroke, not the exhaust stroke (feel the compression with your finger over the spark plug hole). If it's the exhaust stroke, continue rotating the engine another 360 degrees.
* Using a timing light: This is much easier and faster than using the marks. Connect the timing light to the #1 spark plug wire and the battery. Then, crank the engine over and observe the position of the timing mark while the engine runs (briefly). The timing light will flash the timing mark to show you what the timing is set to.
4. Adjusting the Distributor:
Once you've confirmed TDC on the #1 cylinder compression stroke:
* Loosen the distributor clamp bolt(s). This will allow you to rotate the distributor.
* Rotate the distributor: Rotate the distributor slightly, either clockwise (to advance the timing) or counter-clockwise (to retard the timing). A small amount of rotation (a few degrees) makes a significant difference.
* Tighten the distributor clamp bolt(s).
5. Checking the Timing (Re-verification):
* Reconnect the negative battery cable.
* Start the engine.
* Use a timing light (preferred) or the timing marks on the balancer again to check the timing. The recommended timing for a 235 Chevy is typically around 4-6 degrees BTDC (Before Top Dead Center) at idle. This varies based on the year of your engine and specific carburetor setup. Consult a service manual specific to your engine's year and specifications.
6. Adjust as needed: Repeat steps 4 and 5 until the timing is set correctly.
Important Considerations:
* Consult a shop manual: A factory service manual for your specific year 235 Chevy engine will give you the precise timing specifications and valuable additional information. These specifications can vary by year.
* Vacuum advance: The distributor likely has a vacuum advance mechanism. Make sure it's connected and functioning correctly. This will affect timing at higher RPMs.
* Centrifugal advance: The distributor also usually has a centrifugal advance mechanism. This is internal and not adjustable easily unless you rebuild the distributor.
* Smooth idle: The correct timing will result in a smooth, stable idle. If the idle is rough, you may need to fine-tune the timing or investigate other potential issues (carburetor, ignition system).
This is a general guide. Incorrect timing can damage your engine. If you're uncomfortable performing this task, it's best to consult a qualified mechanic.
