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

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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.

Stroker owners should refer to OEM instructions for their specific type of motor, unless the manufacturer recommends entirely different plugs.
Spark plug; 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
W&W# Picture net price* Available from warehouse Germany?
12-001 Spark Plugs #5R6A: Shovelhead 1975→, Evolution Big Twin 1984→ by Autolite; manuf. labelling: 4265 $3.64 each
in stock
12-027 Spark Plugs #5R6A: Shovelhead 1975→, Evolution Big Twin 1984→ by Champion; manuf. labelling: RN12YC $4.18 each
in stock
12-086 Spark Plugs #5R6A: Shovelhead 1975→, Evolution Big Twin 1984→ »OEM«; manuf. labelling: 5R6A; USA $6.22 each
in stock
* United States of America: Tax free shipping. Please check your local import fees.

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