How to Find the TDC of a Chevy 350 With a HEI Distributor

by Jack Hathcoat
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Determining top dead center (TDC) of a Chevy 350 engine is essential if the engine was rebuilt and is ready to be started. When the engine is set to TDC, the number one cylinder is positioned to fire the number one spark plug. That means the piston is at the top of it's compression stroke, both the valves are closed, and the gasoline and air mixture is compressed. When a spark is applied by the spark plug, the cylinder fires and power is transmitted through the crankshaft. Unless the location of TDC is known, the HEI distributor cannot be installed and timed properly.

Step 1

Raise the hood of the vehicle and remove the fuel pump fuse. Use a socket wrench to unscrew the number one spark plug. On the Chevy 350 engine, as you face the engine, this is the right front spark plug.

Step 2

Shine a flashlight on the lower crankshaft pulley, just behind the belt. The pulley bolts to the harmonic balancer, which is directly attached to the crankshaft. A series of timing marks is scribed onto the balancer and one mark is labeled TDC. Locate this mark and highlight it with a paint pen.

Step 3

Crank the engine over and hold a finger over the number one spark plug hole. Have an assistant crank the engine repeatedly until you feel compression pushing out of the hole. When this occurs, the number one cylinder is approaching TDC.

Fit a socket over the crankshaft bolt that holds the harmonic balancer to turn the crankshaft and perfectly align the paint mark on the balancer with the pointer that is bolted or welded to the engine. When the mark and the pointer are aligned, the engine is set and ready for the HEI distributor installation.

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