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estout81 · 08-23-2020, 12:24 PM

Autolite 216 plugs have a 7/16 in. reach, A8 heat range and non res. 425's have a 1/2 in. reach, B9 heat range and are resistor. 4092's are 1/2 in. reach, A9 heat range and non res.
My Offy 400 heads had about 5/8 in. of threads. I used the Autolite 4092 plugs and chamfered the combustion side to remove the excess head threads. For clearance of plug to valve, anything over 1/16 in. should be plenty. I did this several years ago and many miles and the engine runs fine.

08-23-2020, 12:24 PM	#29
estout81 BANNED Join Date: Jun 2010 Location: Utica, Ohio Posts: 522	Re: AutoLite 216's in Offy heads Autolite 216 plugs have a 7/16 in. reach, A8 heat range and non res. 425's have a 1/2 in. reach, B9 heat range and are resistor. 4092's are 1/2 in. reach, A9 heat range and non res. My Offy 400 heads had about 5/8 in. of threads. I used the Autolite 4092 plugs and chamfered the combustion side to remove the excess head threads. For clearance of plug to valve, anything over 1/16 in. should be plenty. I did this several years ago and many miles and the engine runs fine.