Table of Contents
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REF: Tools - 129
Spark Plug Tools
To Gap the Spark Plugs
Spark Plug Hole Adapters for Diagnostic Testing
These are used in place of the spark plug to hook up diagnostic tools (compression tester, leak-down tester etc.).
They can also be used to adapt a 14mm TDC whistle or piston stop to a Sporty engine.
Commercially available
- 12mm adapters are usually supplied along with compression and leak down kits. They are also available at some auto parts stores and online tool companies.
- If you, by chance, have bought a 'kit' in the past only to find your gauges no longer work properly, keep the fittings that came with it before tossing out the defective parts.
These may prove to be invaluable when they are needed.
A few adapters including a tall one (which great for some V-8's). Add the small 14mm-12mm adapter on the long one and it'll work for 12mm plug holes. |
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Spark Plug Hole Thread Adapters 3) |
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Homemade
This is a homemade adapter (1/4” NPT to 12mm) that's relatively simple to make if you are having trouble finding the adapter you need.
A used spark plug is already threaded for the plug hole. You can grind the electrode off and remove the insulator. Then thread the internal hole for the threads you'll be needing from you hose / apparatus 4) |
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You'll need to tap threads into the gutted out portion of the plug. In order to get good threads in the plug body you need a bottoming tap (no taper).
Or, you will have to grind down a 1/4“ NPT tapered tap and make it shorter until it is able to go deep enough into the plug body to cut threads in the sides.
Break the porcelain off with a hammer (eye protection required). Take a small screwdriver and break up the porcelain under the crimp (portion that holds the porcelain in the plug body ), this will let you grind the crimp only and the job will go faster as the porcelain is harder to grind. Then pull the rest of it out. You now have to tap threads in the gutted area for 1/4” NPT (national pipe thread)in the plug body and you are ready to go. 5) |
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Homemade 1/4“ NPT to 12mm Spark Plug Hole Adapter |
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This adapter was made using the same concept of removing the ceramic and brazing a male hose coupling to the end of a spark plug.
Homemade Hose Coupling 6) |
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