J11 spark plug replacement question.

[moxie-man]

I have several 1.25 and 2.5 hp Elgins that are ready to test. Have cleaned the tanks, carbs and the magnetos. I have no original j11 plugs for them. All had j whatever’s plugs but the electrodes are close to flush with the bottom of the plug. Today I went To Sanels auto and purchased 4 Autolite 46 plugs(supposedly equivalent) and the center electrode extends well beyond the bottom of the plugs thread. I believe that the electrode length is wrong. The thread length looks to be correct and matches all the other mis matched plugs. Am I wrong in thinking the electrode center should extend just 1/16 below the thread?

[retiredoz]

According to my old Champion cat, there’s no Autolite equivalent to J11. AC 46 is equivalent. The Autolite plug converts to RF11YC, which is an extended electrode-type not commonly used in old outboards..If you can find an NGK B2, you’re in luck..

[frankr]

Wrong thread length or extended tips present a danger of banging into the top of the piston. On top of that, "R" plugs are resistor plugs, to be avoided in magneto equipped engines. As I have proclaimed many times, plug mfrs are telling us to use anything that will fit the hole, and some that don’t even fit.

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