wrong plugs. any ideas?

[TommyDuncan]

I bought some new plugs for my 305 V6 today. The kid behind the counter was cool and asked lots of questions about my truck.

I was putting the third plug in when I noticed something...
My first thought was "that damned kid gave me 305 V8 plugs!" But then I remembered having a conversation about the V6. Since I have a couple parts motors I decided to look at the plugs in them. They were much longer like the ones he gave me.

It runs MUCH better. I did a few other things to the motor that might have contributed also but what an improvement!

That is quite a difference in heat range...
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[jtrichard]

have any trouble putting them in with dirty threads? napa shows both long and short reach for the 305 V6 more of the long reach

[TommyDuncan]

Originally Posted by jtrichard

have any trouble putting them in with dirty threads?

Good eye! That is actually the plug I took out of the parts motor next to the one I took out of the good motor. I forgot to take a pic with the new one so I took one of it. I cleaned the holes out as good as I could(poor shop vac) before I put the new ones in.

I have friends out that way. One of them used to own one of these V6 rigs. Bob...
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[jtrichard]

i have one in a gmc 2 1/2 ton but don't have any idea what plug is in it....and i did see that both of the plugs in the pic were used i meant the threads in the head i see you said you vac d them

[TommyDuncan]

Originally Posted by jtrichard

i have one in a gmc 2 1/2 ton but don't have any idea what plug is in it....and i did see that both of the plugs in the pic were used i meant the threads in the head i see you said you vac d them

It did feel like there was some carbon build up, like the short plug left some of the threads exposed.
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[jtrichard]

if it takes the long plugs it would leave threads exposed with short plugs in it.... if it takes short plugs then with long plugs you will have threads in the combustion chamber ...either way you need to know what you have for sure

[MusicMan70]

TommyDuncan, Which brand/part number were you given?

[TommyDuncan]

Originally Posted by MusicMan70

TommyDuncan, Which brand/part number were you given?

I went on Rock auto and looked at their selection. I can't remember if I looked up the new ones or the one I took out of the spare motor. I think I bought Plain Champions because the computer at the parts store said OEM but I think I looked up the Autolites that were in the other one. My 05 Wrangler doesn't like fancy plugs so I am in the habit of using cheapies.
I might still have some of the packaging at home to get a part#. I know from Truxton's thread that you are a V6 guy. Do you recommend a certain plug? I have alot to learn about these motors!

[TommyDuncan]

I just looked on Rock auto again and it shows ¾" and ⅜" plugs for the same application. Anyone have any info on this? I dunno how I missed it before?
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[DPowers]

there is a section on spark plugs here

http://6066gmcclub.com/gmcguy/index.php

[TommyDuncan]

I couldn't find anything specific to what I am looking for but he has some GMC ads and one of them says something about new extended reach plugs that have greater contact area for better cooling and longer life. This same ad also mentioned the 2 barrel carb which came in 62. So I am guessing the short ones were for the 60-61s and the longer ones where later?
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[jbgroby]

I went and checked my reference material and the plugs I used were AC DELCO R45S.

Jake
Lacombe, LA.

[MusicMan70]

This info came from the New 6066GMC Forum archives and explains the different plugs.

> > I want to replace the plugs in my 60 305a. It has Autolite 85's in it now but I want to make sure they are the correct ones before I replace them. I went to the parts house yesterday and they gave me some Autolite 66's but they look to be too long. The 85's were a short plug. I dont want to switch and damage my pistons because the plug is too long. I also am not a fan of Autolite.

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.

[TommyDuncan]

Originally Posted by MusicMan70

This info came from the New 6066GMC Forum archives and explains the different plugs.

> > I want to replace the plugs in my 60 305a. It has Autolite 85's in it now but I want to make sure they are the correct ones before I replace them. I went to the parts house yesterday and they gave me some Autolite 66's but they look to be too long. The 85's were a short plug. I dont want to switch and damage my pistons because the plug is too long. I also am not a fan of Autolite.

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.

Interesting! Thanks for the Info. So far I haven't had a problem. I will pull them soon and see how they look.
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[jtrichard]

if you take a piece of wire put a small hook on the end of it you should be able to feel how long the threads are in your head

[tincan1966]

Originally Posted by jtrichard

if you take a piece of wire put a small hook on the end of it you should be able to feel how long the threads are in your head

That's what I would recommend- a couple minutes with a flashlight will tell you exactly what thread depth you have and if tapered seat or flat.