1946 chief spark plug issues???

[jeff47wl]

I have a 1946 indian chief, stock 74" inch. the cylinder heads have brass insert to except 14 miller meter spark plugs. the issue is the brass inserts are sticking up about 1/8 to 3/32 of an inch from being flush with the heads. I tried to run auto lite 303 which have a 3/8 inch reach but they were fouling quick like within less than a 10 mile ride. I have switched to auto lite 4123 which has a 1/2 inch reach ( and a project electrode tip ) to get the electrode further into the cylinder chamber. I have rode it about 18 mile ride and had no issues so far. on the auto lite spark plug chart I can not figure out if a 303 and a 4123 are similar in heat range. looking at the chart they appear to be close just the difference is the reach. any other suggestion would be appreciated

jeff
amca5191

[hairynob24]

i run NGK plugs BP7ES no problems ..long reach

[tomfiii]

Spark plug threads should not be into the chamber past the insert as carbon build up will cause plug to back out insert when hot . You want an extended tip plug . Hard to say why those plugs fowled when others didn't.

[pisten-bully]

...old thread, new question: with using longer OAL sparkplugs, is there an interference issue with removing them from the front cylinder? Not a lot of head room there!

[PRG]

Howdy sir,

Run NGK BL7ES with the threads turned off to the same depth as the original spec plugs to avoid the aforementioned binding on removal from deposits. This places the base of the plug flush with the head surface with just the electrode protruding into the combustion chamber. With Clyde Crouch’s superb electronic ignition fitted this results in far better more efficient ignition and less resulting deposits. But, that same electrode exposure calls for a little bit more care in cold start and initial warmup/clearing out as with rich mixture and raw gas can lead to fouling.

For older members here, think the old plug extension tubes sold by JC Whitney back in the day to get your plugs away from the oil splashing around in your then worn out engine, that essentially is what the original short J6’s do. On the other hand, recessing a spark plug in that well is not efficient.

[pisten-bully]

I'm just curious if there's enough room to maneuver a longer plug into position so that it can be threaded into the hole?

(I don't have the means to machine off some of the threads, either!)

[RonH]

I run Auto lite 63 in my 48 chief.