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How to Gap Chevy 350 Spark Plugs

By: Leon Rhodes

Chevrolet introduced the the first 350 engine in 1967 on Camaro models. In 1968 it was added as an option in Chevy Nova models and in 1969 it became a popular high-performance option on all Chevy vehicles. Having 8 cylinders, Chevy 350 engines require 8 spark plugs to run optimally.

Chevy 350 Spark Plug

Chevy recommends a 0.035 inch gap for 350 small block engines. Spark plugs are typically pre-gapped by the factory to the correct size but you should always double check the gap to make sure using a feeler gauge or coin-style gap tool. It's a good idea to inspect the plugs for signs of water in the fuel.

Method 1 - Using a Feeler Gauge

Here's how with a 0.035 inch feeler gauge: Hold the spark plug firmly with the threaded end up so you can see the electrode. Slide the feeler gauge underneath the spark plug's electrode(typically hook shaped on the end).

If The feeler gauge fits snugly the gap is properly set. If the feeler gauge doesn't fit or is very loose you need to slightly bend the electrode until it's snug.

Method 2 - Using a Coin-Style Gauge

Using a coin-style gauge the process is slightly different: Holding the spark plug in the same manner slide the smallest edge of the 'ramp' on the coin-style gauge under the electrode and turn it until it's snug.

When snug look at the thickness reading printed on the tool and make sure it reads 0.035 inches. Adjust accordingly if required.

Which plugs can I use with a Chevy 350?

The following plugs work on Chevy 350 engines:

  1. ACDelco R44LTS6 Professional Spark Plugs
  2. Bosch 9655 Double Iridium OE Replacement Plugs
  3. DENSO #4511 PLATINUM T T Spark Plugs
  4. ACCEL 0576S-4 Shorty Copper Core Spark Plugs
  5. ACDelco Gold 14 RAPIDFIRE Spark Plugs

What happens if the plug gap is wrong?

If the gap on your Chevy 350 spark plugs is wrong engine performance will suffer. Typically the engine will surge, sputter, vibrate and possibly stall. For optimal performance, on old engines or on the newer 5.7L 350 V-8 engines, proper gap size is 0.035 inches.

Why does spark plug gap change?

Over time engine spark plug gaps can change due to wear. Fouled plugs, those burning oil, will become covered in carbon deposits effectively narrowing the gap. Conversely, lean engine conditions can cause excessive heat to weaken the spark plug electrode enough to make the gap widen.

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