Where is Number 1 on a HEI Distributor Cap?

Published by Dustin Babich on

In a High Energy Ignition (HEI) distributor system, identifying the position of the number 1 terminal on the distributor cap is crucial for proper engine timing and firing order. The location of the number 1 terminal can vary depending on the engine and distributor design, but there are general guidelines you can follow to find it:

Introduction to HEI Distributor Systems

HEI distributor systems are widely used for their efficiency and simplicity. They integrate the ignition coil into the distributor cap, reducing wiring and improving spark energy. Properly orienting the distributor cap and knowing the location of the number 1 terminal is essential for correct engine operation.

Locating the Number 1 Terminal

Initial Identification

  • Manufacturer Markings: Some HEI distributor caps are marked with a “1” or another identifier to denote the number 1 terminal. This is the starting point for the engine’s firing order.
  • Reference to the Engine: If the distributor cap is not marked, the number 1 terminal is typically positioned according to the engine’s design. For example, on many V8 engines, the number 1 terminal is often found towards the front of the engine, closer to the number 1 cylinder.

Engine Cylinder Layout

  • V8 Engines: For many American V8 engines, such as those found in Chevrolet or GMC vehicles, the number 1 cylinder is usually located on the driver’s side, frontmost cylinder. The distributor cap should be oriented so that the number 1 terminal aligns with the direction of the number 1 cylinder.
  • Inline and Other Engines: On inline engines, or different configurations like V6s, the number 1 cylinder is typically at one end of the engine block. You’ll need to align the number 1 terminal on the distributor cap with the number 1 cylinder accordingly.
READ ALSO  Marine 350 VS Automotive 350 Differences

Setting the Distributor Cap

Aligning with the Rotor

When installing the distributor cap, ensure that the rotor points to the number 1 terminal’s position when the number 1 cylinder is at top dead center (TDC) on the compression stroke. This ensures that the spark occurs at the correct time.

Firing Order

Once you’ve identified the number 1 terminal, the rest of the wires should be connected according to the engine’s firing order, which follows in a clockwise or counterclockwise direction, depending on the engine design.

Tips for Correct Installation

  • Manual Reference: Always refer to the vehicle’s service manual for specific information related to the engine and distributor cap installation.
  • Marking the Cap: If the cap is unmarked and you’ve determined the number 1 terminal’s position, consider marking it yourself for future reference.
  • Checking Engine Timing: After setting up the distributor cap, it’s advisable to check the engine’s timing with a timing light to ensure everything is correctly aligned.


Identifying the number 1 terminal on an HEI distributor cap is a key step in setting up your engine’s ignition system correctly. The position can vary, but it’s typically aligned with the number 1 cylinder, and orientation can depend on engine design. Always consult the service manual for your specific vehicle and engine for precise installation instructions.


Can I use any HEI distributor cap for my engine?

It’s important to use a distributor cap that is designed for your specific engine type to ensure proper fit and function.

What happens if I get the number 1 terminal wrong?

Incorrectly identifying the number 1 terminal can lead to improper engine timing, misfires, and potentially prevent the engine from starting.

READ ALSO  Uncovering the Mystery of 400 Sbc Bored 60 Over: Explained

Is it easy to adjust the distributor if I make a mistake?

Yes, you can adjust the distributor by loosening its mounting bolt and rotating the distributor body until the rotor aligns with the correct position for the number 1 terminal.

Can I mark the number 1 position on the distributor cap myself?

Yes, if the cap is not marked, you can mark the number 1 position yourself using a permanent marker or paint for future reference.

Dustin Babich

Dustin Babich

Dustin Babich

As the passionate author behind Automotivesimple.com, Dustin Babich is a knowledgeable expert in all things automotive. With a deep understanding of car tools, equipment, engines, and troubleshooting techniques, Dustin Babich shares invaluable insights, practical tips, and effective solutions to empower readers in overcoming car-related challenges.

As an Amazon Associate, I earn from qualifying purchases. This will not charge you any extra cost.