View Full Version : Chief spark plugs
06-02-2010, 02:36 PM
Off hand, what's a good spark plug for a 74" Chief ?
Champion J6's have been the default install for years but being short reach (recessed in the head) are sort of a version of the old JC Whitney plug extension once sold to prevent oil fouling on oil burning engines by moving the plug away from the combustion chamber. These really hinder flame propogation during the combustion process and result in the appearance of a "richer" running engine when in actually it may not be, actually just an inefficient one.
I run full length/extended tip plugs in both of mine. When you view the underside of the head, the plug itself comes right to the surface of the head with the electrode nicely exposed. One machine has full depth inserts so I can just screw these plugs in unaltered. The other one has the traditional shorter inserts so I just turn off about 40% of the length of the threads on the plug.
If your machine's an oil burner like one of mine, I'd just keep it at the cross reference to a J6, if a clean motor, maybe a step colder to reduce detonation tendencies.
06-03-2010, 12:10 PM
Thanks Peter. I wasn't sure if there was a "new" preferred plug these days. I'll get a pair of J6 Champions today. I appreciate your observations and insight.
06-04-2010, 12:30 PM
Another choice is to use a reproduction plug.
Our new plugs look correct, and work properly, and cost the same as a Champion J6 plug
Get that last point on your restorations using our latest addition for your Indian Motorcycle. We have reproduced the Indian "C" Script Spark Plug, complete with a collector Indian Script Box.
The "C" is the most common heat range used on our Indian Motorcycles
This is a 1/2" reach plug (Indian originaly used a 3/8" reach). It is completely interchangeable with the 3/8 plugs on all heads.
The plug is equivalant to a NGK B7HS or Champion J6.
We designed this plug to be used! Not placed on a shelf and looked at. Although, you may want to order a set for your memorabilia collection!
LINK: (https://www.starklite.com/indian-motorcycles/pc/PLUG-INDIAN-SCRIPT-SPARK-37p390.htm) for more info.
06-21-2010, 10:18 PM
Eric- I use original Indian C's in both my 74 chiefs and have never had a problem. You can still find them (I just got two nice used sets at rhinebeck for 75 a pair). The Bs are generally good for 30s chiefs (I run them in my 37 but they are very hard to find and much more expensive). Nothing against the repo Cs but just thought you might also want a set of real ones to run around the meets with.
06-22-2010, 09:47 AM
Parkerize, thanks for the information. I'll keep my eyes peeled (disgusting thought) for a set of genuine C's and I think I will get a reproduction set from Starklite too. I'm still having battery problems and have yet to receive the 6V Yuasa battery that I ordered a month ago. I am now giving serious consideration to converting to 12 volt because I love the way this Chief handles and the way it puts out power. It's a fun motorcycle that is mechanically very reliable but is a bummer, electrically. My friend Indianut converted his 1940 Chief to 12V and has zero problems with it. I think I need to take a close look at his bike and see what he did.
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