Packard Forum Index » Post-War (1946-54)

Hi all
I picked up new plugs this week and went to install them today. The new plugs are from NAPA and they had champion RJ12C listed. The old plugs are AC R46SZ. The new champion plug is about 4mm shorter tham the AC plug and I am not sure which one is correct.

Any comments

Thanks

According to spredsheet listed earlier

1951 Champion rj12c/AC c47/autolite 358-hope that helps

I believe AutoLite's current recommendation is #308.

Thanks , I guess the champions are right. What was the list you mention. I did a search and could not find any history on spark plugs.

From a spreadsheet put together by Albert some years ago-who lives in Toronto I believe

This discussion thread, and previous ones dealing with spark plug heat range have reminded me of another factor to keep in mind. Problems are created by using the wrong reach spark plugs. Reach is the length of the threaded part of the plug. I forget the reach specs, but for the sake of conversation let's say for a 14mm plug of the proper heat range they come in 3/8" and 7/16" reach versions.

Using a 3/8" reach plug where a 7/16" plug is required will result in the bottom threads of the spark plug hole becoming clogged with carbon deposits. No problem until one tries to screw in the proper reach plug. The plug may not be able to be installed and damage to threads on plug or head may result. Running a tap into the hole will clean up the treads.

Using a 7/16" reach plug where a 3/8" plug is required will result in the bottom threads of the spark plug becoming clogged with carbon deposits. Problems occur when one tries to remove the plug. The carbon clogged bottom threads will prevent the plug from being removed and will cause damage to the threads of the plug and head. This may require removal of the head to repair the damaged spark plug hole threads.

Be careful in selecting the correct heat range, reach, and type (resistor/non-resistor) spark plug. The spark plug you remove and try to match may not be the correct one. Refer to a chart for the correct application. Brand is not important. Also, extended or protruding electrode type plugs should not be used in our flathead Packards.

Some Packards use the small 10mm spark plug, and some V-8 Packards use a 14mm plug with an extra long reach. These are special discussion topics, and not covered here. Others here may wish to add to this topic, and their contributions or comments are welcome. Thank you.

(o[]o)

Thanks again, if anyone has the spreadsheet, I would appreciate a copy. It is indeed the "reach" that is differant with the new plugs being shorter however it sounds like the subject has already been beaten to death so I will try again to searh for history. If I understand correctly, the plug threads should be the same as the head thread depth.

Also, if Albert is out there, I would like to get in touch and meet the local Packard gurus. My project is getting close and I am hope to have a spring start-up.

Perhaps these attachment files will be helpful. Its from 1962 AC catalog. Middle column is plug gap, right-most column is distributor point gap.

In finding the correct spark plugs for almost any vintage vehicle back to at least the 20s, I've always found the AutoLite website look-up to provide correct choices. You'll have to rattle around the sitel go to "application lookup", then select "spark plugs", you'll come on a set of dialog boxes for make of car, year, model, and engine. You'll get a recommended currently available AutoLite plug; I understand these recommendations were adjusted some years back to provide the best choice for current gasolines.

Attach file:

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Drat, another engine to look up. I wonder where they found the extra two cubic inches???
Were you just checking again??