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Spark Plugs
Spark Plugs #3-4: Big Twin 1948-1974, KH+XL  1954-1978

Spark Plugs #3-4: Big Twin 1948-1974, KH+XL  1954-1978

  • fits Big Twin 1948-1974, KH+XL  1954-1978, Servi-car 1956-1973
  • porcelain / steel
  • thread: M14 x 1.25
  • thread length: 3/8 ”
  • wrench size: 13/16 ”
  • heat range HD-code: 3-4
  • replaces Harley-Davidson part number 32303-47A, 32305-48A, and 32301-60

Spark Plug Heat Ranges

Harley spark plug heat ranges are marked by numbers, from 2 to 12. No. 2 is the hottest plug, no. 6 would then be a relatively cool plug. The coolest plug used by Harley-Davidson is marked 10R12A. Double numbers characterize multi-range plugs.

With older motors, it was not uncommon, that you achieved an optimum with plugs of two different heat ranges. Unlike the well known prejudice implied, you had to choose cooler plugs for the front and hotter plugs for the rear cylinder. On later Harley engine designs, heat distribution is balanced to such an extent that you should not have to rely on those tricks anymore.

Item №
net price*
Availability in warehouse Germany
Spark Plugs #3-4: Big Twin 1948-1974, KH+XL  1954-1978
by Champion; manufacturer-code: RJ12YC
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Spark Plugs #3-4: Big Twin 1948-1974, KH+XL  1954-1978
»OEM«; Mexico
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* United States of America: Tax free shipping. Please check your local import fees.

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