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Spark Plug Adapter 18 mm to 14 mm (set of 3)


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Spark plug adapter, 18 mm to 14 mm, set of 3.

2 in stock


These spark plug adapters allow for easy conversion from [vintage] 18 mm spark plugs to the [modern] 14 mm standard. Offered here in a set of (3) for use in the SAAB two-stroke engines.

But why?

  • First of all, the old 18 mm style plugs are becoming harder to find and more expensive as time goes on.
  • Secondly, the 14 mm style plugs are the current standard and that is where the spark plug companies are putting all their best and newest technology.

No one is putting research and development into the 18 mm plugs. You are basically buying a 1950’s plug, at best.

Modern plugs offer precious or semi-precious metal electrodes that are far better at resisting fouling and are much longer lasting. Modern style plugs are often required to use the electronic ignition upgrades that can make our vintage cars more reliable, more efficient, and better running.

My adapters are machined from 360 brass and come fitted with a copper sealing washer.

Brass is my preferred material for this application for the following reasons:

  • It is chemically non-reactive in both aluminum and iron cylinder heads, avoiding corrosion issues in either case.
  • It has far better heat transfer properties than stainless steel.
  • It just looks cool.

My design is optimized for NGK plugs, but will work with any manufacturer’s plug. NGK put the hex higher on the body of the plug than other manufacturers, so I have used that additional space to make the hex on my adapter slightly taller. This make it easier to install and stronger. The adapter will work perfectly well with other manufacturer’s plugs, but I think it is worthwhile to mention this feature of the design.


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