HD or NGK spark plugs
Extreme HDF Member
Joined: Jun 2011
Posts: 10,216
Likes: 224
From: Glendale AZ
Yeah not to hyjack this thread either but lets hear more about 'Indexing' since its supposed to be more about that than brand type the OP was inquiring about....
Outstanding HDF Member
Joined: Jan 2010
Posts: 2,916
Likes: 31
From: earth
Yes, open side of the gap facing the intake valve. Indexing and side gap, aka trimming the ground strap, unshrouds the spark promoting hotter quicker flame front propogation and a self-cleaning condition because every A/F charge "washes" through the open gap. I've done it with Stock HD 6R12, colder HD 10R12, and Autolite 4163 all about the same results. Not necessarily a big power gain in a twin but much smoother idle and acceleration.
Outstanding HDF Member
Joined: Jan 2010
Posts: 2,916
Likes: 31
From: earth
Good article in the link. So where can we get indexing washers from?
http://youroilshop.com/plugs.htm
http://www.debrix.com/SPARK-PLUG-IND...p/3-271-mw.htm
http://www.sudco.com/spark.html#wash (bottom of page)
http://www.thunderproducts.com/Spark...g%20Washer.htm (not sure if these are 12mm)
http://www.jacobselectronics.com.au/accessories.htm
http://www.zippersperformance.com/ca...=583&prod=2280
http://www.nrhsperformance.com/partsignition.shtml (bottom of page)
Extreme HDF Member
Joined: Jun 2011
Posts: 10,216
Likes: 224
From: Glendale AZ
Probably a little of both, its rather rare for a blueprint to dictate that a thread starts in a specific location, even so tolerance would still be a factor preventing perfect index alignment out of the box.
Good article in the link. So where can we get indexing washers from?
http://youroilshop.com/plugs.htm
http://www.debrix.com/SPARK-PLUG-IND...p/3-271-mw.htm
http://www.sudco.com/spark.html#wash (bottom of page)
http://www.thunderproducts.com/Spark...g%20Washer.htm (not sure if these are 12mm)
http://www.jacobselectronics.com.au/accessories.htm
http://www.zippersperformance.com/ca...=583&prod=2280
http://www.nrhsperformance.com/partsignition.shtml (bottom of page)
Good article in the link. So where can we get indexing washers from?
http://youroilshop.com/plugs.htm
http://www.debrix.com/SPARK-PLUG-IND...p/3-271-mw.htm
http://www.sudco.com/spark.html#wash (bottom of page)
http://www.thunderproducts.com/Spark...g%20Washer.htm (not sure if these are 12mm)
http://www.jacobselectronics.com.au/accessories.htm
http://www.zippersperformance.com/ca...=583&prod=2280
http://www.nrhsperformance.com/partsignition.shtml (bottom of page)
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
As far as I've known indexing, it's not as much "getting the perfect path" for the spark to hit the flame front, but rather just not allowing the ground bar to barricade (shield) it from the fuel. In other words, there is margin for error.
I've seen a set of plugs screwed into the same hole and index themselves in six different directions, so evidently they are run randomly thru assembly in regards to that.
I've seen a set of plugs screwed into the same hole and index themselves in six different directions, so evidently they are run randomly thru assembly in regards to that.
Outstanding HDF Member
Joined: May 2008
Posts: 2,543
Likes: 19
From: Ashland Ohio
Plugs will indeed change the anti knock feature inside of the ECM. This really does exists, all one needs to do is ask any decent tuner. On Delphi EFI bikes... one will notice if they pull the plugs, hook a wire to one and spin the engine... the spark will try a few times and die with no spark. This is because the plugs do not see the correct resistance (compression makes it harder to fire a plug than in free air).and kills the plug firing.
I think any 'normal' type plug is OK. I simply run HD plugs because the dealer is close.
I think any 'normal' type plug is OK. I simply run HD plugs because the dealer is close.