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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old May 6th, 2021, 05:20 PM
BobShing BobShing is offline
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Default GMC V-6 ignition question

I have a 63 GMC pickup with a 305, and have noticed there seems to be 2 types of distributors for this engine. Mine has the externally adjustable points (window like v-8 distributors). I think I have seen pictures of other 305s with distributor caps that resemble in line 6 type. Anyone know if thereís a year or model changeover point? Or am I mistaken?
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Old May 6th, 2021, 08:33 PM
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Default Re: GMC V-6 ignition question

60-66 has window. Probably changed in 67 or late 66
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Old May 6th, 2021, 08:40 PM
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Default Re: GMC V-6 ignition question

Post from the archives by Pete Chronis;

The other thing I'd like to bring up is the early distributor had the advance weights on top just like the V8 models and the housing was cast iron, the later small cap distributor housings were cast out of aluminum and the weights were mounted below the point and condenser plate. Right around 1964 the smaller distributor came in to supersede the big cap distributor though some larger series trucks and engines still used the big cap distributor through 1965.
Pete Chronis Northern Cal.
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Old May 6th, 2021, 08:54 PM
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Default Re: GMC V-6 ignition question

This item is confusing because our own "known good parts" shows both types for the same year motors. Rockauto shows window up to 65-66.
Jolly shows two types of caps and two types of vac advance depending on the distributor weight design as Pete says. Parts are shown for same years 63-66. As Pete says, some motor had one way and some another.
This may conflict a little with Pete and I am not an expert but, sounds like early (60-62) caps were known as small cap and has clips to hold the cap on. Also the rotor was slip on with weights under plate. 63-65 sometimes called "large" cap and have "L" pins holding cap on, under rotor weights and screw on rotor. The cap had a window. I said confusing, right?
As far as I can tell the answer to the question is no window 60-62, window 63-65, no window 66-up.

I don't know if there was a clip-on cap for 305 V6 or not. Sometimes the I6 stuff gets confused with V6 stuff. BUT: The Chevy I6 in 60-62 had a clip-on cap. No window in I6, window in V8's. Then in 63 went to "L" pin.

Last edited by AZKen; May 6th, 2021 at 10:22 PM.
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Old May 7th, 2021, 01:32 AM
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Default Re: GMC V-6 ignition question

Thanks for the answers! Iím assuming the points are identical to their v-8 counterparts, although the condenser is likely a different value...Iíll look it up.
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Old May 7th, 2021, 07:40 AM
bigblockv6 bigblockv6 is offline
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Default Re: GMC V-6 ignition question

There was never a small cap clip on distributor used on GMC V6 engine. The big style cap with the window was used from 1960-65 but around 1965 and even possibly 1964 the small cap, same one used on inline sixes was used on light duty engines while bigger trucks still used the larger window style cap, by 1966 all V6 engine came with the small cap distributor. I don't know why they made the change but the larger cap distributor makes better sense to me because you can adjust the points externally.
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Old May 7th, 2021, 10:32 PM
George Bongert George Bongert is offline
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Default Re: GMC V-6 ignition question

Quote:
Originally Posted by BobShing View Post
Thanks for the answers! Iím assuming the points are identical to their v-8 counterparts, although the condenser is likely a different value...Iíll look it up.

Greetings Bob!

The points are indeed the same as their V-8 counterparts. There is (or was) a unitized point set that included the condenser which made installation much easier, since you didn't have to fiddle around with a separate mounting screw for the condenser, and the wire on the condenser was also eliminated. See if you can still get the unitized point set. It's definitely a time and cuss saver!
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Old May 8th, 2021, 06:10 AM
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Default Re: GMC V-6 ignition question

Quote:
Originally Posted by bigblockv6 View Post
There was never a small cap clip on distributor used on GMC V6 engine. The big style cap with the window was used from 1960-65 but around 1965 and even possibly 1964 the small cap, same one used on inline sixes was used on light duty engines while bigger trucks still used the larger window style cap, by 1966 all V6 engine came with the small cap distributor. I don't know why they made the change but the larger cap distributor makes better sense to me because you can adjust the points externally.
Just an FYI --

If you're interested in getting rid of your points and condenser, Pertronix makes kits for both types of distributors used on our V6 engines. They're simple to install. I've installed many of them over the years.
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Old May 8th, 2021, 09:24 PM
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Default Re: GMC V-6 ignition question

all GMC V6 engines through 1963 used the window type of distributor. The change was made in 1964, when GMC went to an alunimum distributor housing and in the interest of interchangeability with other 6-cylinder engines in production (230-250-292) the change was made. All replacement distributors are of the 2nd design and were installed in older engines when a distributor was needed.
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Old May 16th, 2021, 02:55 AM
POWERSTROKE POWERSTROKE is offline
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Default Re: GMC V-6 ignition question

Quote:
Originally Posted by George Bongert View Post
Greetings Bob!

The points are indeed the same as their V-8 counterparts. There is (or was) a unitized point set that included the condenser which made installation much easier, since you didn't have to fiddle around with a separate mounting screw for the condenser, and the wire on the condenser was also eliminated. See if you can still get the unitized point set. It's definitely a time and cuss saver!
GEORGE - Delco called them Uni-points, points & condensor combined. I used them in my annual tune-ups in my '70 Nova with 307 from about 1974 thru 1977. I had a bad wire on a condensor leave me stranded late one night. Not even having a condensor wire was a good thing in my book.
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