Stovebolt.com
Posted By: dougs AC R45S Spark Plug - Mon Jun 22 2020 06:15 PM
Has anyone used a AC R45S spark plug on a 1955 235 engine and what is the advantage over a regular R45 Plug?
Posted By: Hotrod Lincoln Re: AC R45S Spark Plug - Mon Jun 22 2020 06:35 PM
Be careful- - - - -I believe the "S" stands for "short". The threads of the plug aren't long enough to fully engage the female threads in the head, resulting in the bottom threads being exposed to combustion gases. They will get clogged with carbon, or possibly get burned away by the heat of the combustion chamber.
Jerry
Posted By: BC59 Re: AC R45S Spark Plug - Mon Jun 22 2020 07:47 PM
The S in the AC plug number stipulates a projected tip. This was used to prevent fuel fouling at low speeds and also to cool the spark plug at higher speeds.
Thread length is the same between the 2.
Posted By: Wrenchbender Ret. Re: AC R45S Spark Plug - Mon Jun 22 2020 08:51 PM
I agree with BC. It is a much better plug then the older stile. They are for o-head valve engines only.

George
Posted By: tclederman Re: AC R45S Spark Plug - Mon Jun 22 2020 09:28 PM
Here are images of different AC Delco "R45" spark plugs:
R45
R45S
R45TS

Attached picture AC R45 professional  plug 41Yu+PCV-bL._AC_UL160_.jpg
Attached picture AC R45 S plug 61UhlDL7LyL._AC_UL160_.jpg
Attached picture AC R45 TS  21Sj91p0ebL._AC_UL160_.jpg
© The Stovebolt Forums