Spark plug reach into the cylinder

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Spark plug reach into the cylinder


Post by 64DUOGLIDE » Sun Jan 01, 2006 5:38 am

Description: How far should the plug reach into the cylinder

I can't remember the last time I had a panhead in hand...How far should the plug reach into the cylinder? My autolites are about 1/8" shy of reaching into the combustion chamber?!?



Re: Spark plug reach


Post by harleydoug » Tue Jan 03, 2006 3:37 am

Sounds a little short to me. Usually the plug should be just short of flush, maybe .010 recessed. Pan plugs in H-D heads should be torqued COLD to keep from pulling the steel insert free from the aluminum head. Yes, I know that the plug fouls and you replace it with the engine hot. Just remember to take it easy with the wrench when it's hot.
Is your autolite plug a specific pan plug, or something close from a cross refrance book?? It might be worth your while to get a correct plug and compare it. If the plug hole has bare threads showing in the combustion chamber, it could lead to pre ignition when it gets hot

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