Re: 14 mm/10 mm plugs?

Posted by Owen_Dyneto On 2018/11/10 21:57:01

Packard kept with 10mm plugs until partway thru the 23rd series (1949/50), as did Buick and a few others. They may have later offered service heads for your car in 14mm, I don't recall but others will no doubt comment, in any case the answer should be in the parts list or service letters which are available to you here.

However, many the corner gas stations made nice money doing conversions to 14mm. Easy to tell if your head is off if you were so converted. Since the 14mm have a greater depth of thread, if converted a few turns of plug threads will protrude into the combustion chamber when the plug is installed. These tend to fill with carbon and sometimes make plug removal problematic.

Autolite 306 is a suitable 14mm plug and available at any good local parts store.