Spark Plugs #6-10: Milwaukee-Eight
- Spark plug by Champion
- fits Touring 2017→, Softail 2018→
- steel / ceramic
- thread: M10 x 1.0
- thread length: 19 mm
- wrench size: 16 mm
- manufacturer-code: RG6HCC
- replaces Harley-Davidson part number HD 31600012
- gross weight: 36 g
Spark plugs for air-cooled Harley-Davidson motorcycles. For model application and further details pls see the listed facts, OEM part n°s are given for reference use only.
Wide-range small diameter plugs (M10 x 1 threads!) are just the right thing for air-cooled and twin-cooled Milwaukee Eight sleds. Four large valve heads do not leave too much space for spark plugs in the combustion chamber.
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 08:00-17:00 CET, Fridays 08:00-16:00 CET, Phone: +49 / 931 250 61 16, eMail: service@wwag.com