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GMC V6 and V12 Engines Engine repair and rebuilding

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Old August 26th, 2014, 04:24 AM
Tfish Tfish is offline
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Default Spark plug reach

I am new to the site, and I hope this is the correct place to ask this question. I have a 1960 GMC 1/2 ton fender side that has been in my family since new. I am pretty sure there have been no major modifications to the motor. Whenever I search for spark plugs, I am offered two choices: with a 3/8" reach and a 3/4" reach. I saw on the engine data page that the AC4 was a good plug for the 305E (3/4"), but since I started being the primary caregiver for my 305A, it had and I continued to use the 3/8" reach plug. The question is can a 3/4" reach plug be used safely in a 305A? They are a little easier to find, and it would seem to be a better ignition if the plug were more central to the combustion chamber. Thanks for all the input and advice.
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Old August 27th, 2014, 03:50 AM
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Funky61 Funky61 is offline
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Default Re: Spark plug reach

Hello TFISH and welcome!

Here is info out of the archives courtesy of Pete Chronis concerning this issue.
How about some photos of your family truck?

Quote:
Steve, Absolutely do not use the longer reach plug in your engine, earlier V6
engines had the shorter reach plugs. The AC spark plug number for your 305a could have well been an AC-C44-S which doesn't exist anymore. From what I could figure out checking the tune up specs on these engines is GMC switched over to the longer reach plug in 1963 and used them up to 1972. In 1973-74 the 379, 432
and 478M engines got new tapered seat plugs with much shorter reach than what you have. In my collection of five V6 engines four have the long reach plugs and only the 1973 478M has the short tapered seat plugs. I have a 66 351E that has the Autolite 65 plug which is one step below in heat range to the 66 plug and it is the long reach plug. You may not like Autolite but it is a much better plug than Champion plugs so your choices may be limited here. Pete Chronis Northern Cal.
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Old August 27th, 2014, 05:11 AM
Tfish Tfish is offline
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Default Re: Spark plug reach

Thanks for the reply and info. That is exactly what I needed to know. And he's right, choices are limited and Autolite has been my choice of the few available.

I will try to find some pix of the truck and post them. I am very new to this stuff, so it might take me a little time to do both. Anyway, it's not much to look at as it is. Mechanically, it's in pretty good shape, but it has been undergoing a rolling "paint and body job" for the past few years, started by my uncle. It's original green paint is dull and has many primer spots on it, and the white bumpers and grill have been stained red by its life in the South Georgia clay. It's appearance prompted my then 10 year old niece to say it looked like a "booger," a nickname that has stuck with it...
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