Quote:
Originally Posted by estout81
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.
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Did a search on auto lite sited and could find nothing that tells me what A9 and B9 are