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Spark Plugs #5R6A: Shovelhead 1975→, Evolution Big Twin 1984→

Spark Plugs #5R6A: Shovelhead 1975→, Evolution Big Twin 1984→

  • fits Shovelhead 1975→, Evo Big Twin 1984→
  • also for: S&S engines and cylinder heads
  • thread: M14 x 1.25
  • thread length: 3/4 ”
  • wrench size: 13/16 ”
  • OEM labelling: 5R6A
  • replaces OEM 32312-77, 32311-83, and 32342-04

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.

Have any questions?

Our service team will be glad to help out: Mondays - Thursdays 09:00-16:00 CET, Fridays 08:00-16:00 CET, Phone: +49 / 931 250 61 16, eMail: service@wwag.com