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GMC V6 and V12 Engines Engine repair and rebuilding

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  #21  
Old December 26th, 2015, 03:31 AM
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Default Re: SO who came up with the GMC V6's???

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Originally Posted by bigblockv6 View Post
That was a sad day for me back in Nov 1974 when went over to our GMC dealer to pick up a new light switch for the 68 before my father found out I broke it to pieces, I was only 15. Anyway there was not one Medium duty truck or larger 7500 series truck on the lot with a V6. I was quite surprised to see a J-7500 series with a 427 V8 for the first time. Some 6 months prior to that just about every medium duty( at least 25-30 trucks) all 7500 series trucks were V6 equipped, my impression then was the V6 was alive and well and they had no problem selling them off. Funny thing was in November there was still quite a few V8 74 medium duty trucks left over with the mix of 75 models.
Would have been nice if they kept the V6. But the problem is every darn person has to have that stinkin 350. And because of them, guys like us who want to keep the v6 almost can't because parts are getting more and more scarce by the day. It makes me upset when I see people on forums that have a really NICE gmc with a good running V6....and what's the First thing they say..."I'm gonna swap it for a 350 and th350" Its like Really? REALLY? You couldn't have bought a Chevy and gone cheap on that? I don't know, its just sad to see perfectly good engines go to the scrap yard cause people don't think they are worth anything.
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  #22  
Old December 26th, 2015, 05:46 PM
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Default Re: SO who came up with the GMC V6's???

I've always said that the sbc 350 is a major national obsession When these guys talk about doing this swap they think it's like something real special, there are so other many alternatives today like the newer GM LS engines. I like the idea of just going to a larger displacement V6 specially 401 and up and there you have a substantial power increase and something that's different than that ubiquitous generic bowtie powerplant
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  #23  
Old December 27th, 2015, 01:21 AM
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Default Re: SO who came up with the GMC V6's???

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Originally Posted by bigblockv6 View Post
I've always said that the sbc 350 is a major national obsession When these guys talk about doing this swap they think it's like something real special, there are so other many alternatives today like the newer GM LS engines. I like the idea of just going to a larger displacement V6 specially 401 and up and there you have a substantial power increase and something that's different than that ubiquitous generic bowtie powerplant
I hear ya! Lotta people are so stuck on "Best bang for the buck" "If it ain't cheap it ain't worth it" and all that stuff. Its like really....why do you need to go 0 to 55 in 2 seconds? My 305 pulls me to 55 no problem...not as fast as a 350, but it still does effortlessly. And sounds so dang good to! lol
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  #24  
Old December 28th, 2015, 03:05 AM
BobBray BobBray is offline
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Default Re: SO who came up with the GMC V6's???

The GMC V-6 family of engines was designed in the late 50's to replace the two series of GMC manufactured straight 6's along with the 'borrowed' Pontiac and Oldsmobile V-8's. The V-6 idea was actually very rational as the majority of truck engines at the time were 6 cylinders. A 60 degree 'V' design was selected for compactness, 120 degree firing intervals, and a short strong crankshaft. The engines were very 'oversquare' (large bore, short stroke) to provide flat torque curves and low piston speeds. Most every other feature of these engines was designed for maximum durability, like oversized water and oil pumps, large bearings, and high quality materials. For very large trucks and fire apparatus, the basic design could be stretched into a V-12 (later a V-8 as well). It would seem that the design was intended from the start to be made in a diesel version as well.

No question the GMC V-6 was far more durable than any contemporary passenger car/light truck engine, but I think it is interesting to compare the V-6 to contemporary medium/heavy truck gasoline engines. Again, the GMC proved superior to engines like the International Red Diamond and V-401/478/549, the Ford Super Duty 401/477/534, and the REO (later White) V-8's. The GMC's matched or beat those other engines in output but were more durable, lighter (I know, hard to believe!), more compact, and delivered better fuel economy.
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  #25  
Old December 28th, 2015, 04:04 AM
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Default Re: SO who came up with the GMC V6's???

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Originally Posted by BobBray View Post
The GMC V-6 family of engines was designed in the late 50's to replace the two series of GMC manufactured straight 6's along with the 'borrowed' Pontiac and Oldsmobile V-8's. The V-6 idea was actually very rational as the majority of truck engines at the time were 6 cylinders. A 60 degree 'V' design was selected for compactness, 120 degree firing intervals, and a short strong crankshaft. The engines were very 'oversquare' (large bore, short stroke) to provide flat torque curves and low piston speeds. Most every other feature of these engines was designed for maximum durability, like oversized water and oil pumps, large bearings, and high quality materials. For very large trucks and fire apparatus, the basic design could be stretched into a V-12 (later a V-8 as well). It would seem that the design was intended from the start to be made in a diesel version as well.

No question the GMC V-6 was far more durable than any contemporary passenger car/light truck engine, but I think it is interesting to compare the V-6 to contemporary medium/heavy truck gasoline engines. Again, the GMC proved superior to engines like the International Red Diamond and V-401/478/549, the Ford Super Duty 401/477/534, and the REO (later White) V-8's. The GMC's matched or beat those other engines in output but were more durable, lighter (I know, hard to believe!), more compact, and delivered better fuel economy.
WOW! Thanks the sharing! Has anyone dynoed these that you know of? I'd be interested in seeing the torque curve. A friend of mine said the main bearings on these were as big as a 7.3 diesel engine's main bearings. I know GM made the toro flow but from what I've been reading it wasn't a very good success? There is one for sale about 45 minutes from me for $500. Supposedly runs to. Wow...a GM V6 being lighter than something is surprising. lol Thanks.
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  #26  
Old December 28th, 2015, 04:55 AM
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Default Re: SO who came up with the GMC V6's???

The main bearing journal got even bigger on 73-74 478M V6 engines, bigger main caps, larger bolts ad just a lot more reinforcing in the main saddle area.
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  #27  
Old December 28th, 2015, 03:20 PM
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Default Re: SO who came up with the GMC V6's???

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The main bearing journal got even bigger on 73-74 478M V6 engines, bigger main caps, larger bolts ad just a lot more reinforcing in the main saddle area.
Any particular reason why that you know of? Like they weren't big enough already. lol!
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  #28  
Old December 28th, 2015, 05:16 PM
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Default Re: SO who came up with the GMC V6's???

Nothing that I heard of but in 73 the whole line of V6 engines other than the 305(the 305 originally was slated to be discontinued for 72 but they decided to keep it going) went through upgrades. The gas engines only used 2 bolt main yet the Diesel versions had 4 bolt mains, actually cross bolt mains. Possibly there may have been some bottom end failures with 478's in the 7500-8500 series trucks, I have a 73 478M and the main caps are so much larger and contour better with the bottom of the block. I'll takes some pics of both the new style caps and old caps for a comparison and post them sometime this week.
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  #29  
Old December 29th, 2015, 05:39 PM
Dave Boboltz Dave Boboltz is offline
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Default Re: SO who came up with the GMC V6's???

I worked at GMC Truck and Coach in Pontiac beginning in 1974 as a co-op student, but by that point in time, the area of Plant 2 along South Boulevard where the V6 and V12 were made was not being used much, maybe only for service parts. The part of the plant where the engine line was located was called building 29. All of the tooling was shipped out around 1977 to make room for the GMC Motor Home in building 29. The Motor Home had been built in Plants 3-4-5 on the other side of Woodward, and was relocated so the G-van could be built there. I don't know where the engine tooling went.

I reviewed the James Cleary email from 2004 and I only recognized one name from the list of people that helped design the engine. I have a friend who told me that his father is listed on one of the patents for the engine (last name is Sherrick).

Dave Boboltz, Waterford MI, 1964 K1002 305E
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  #30  
Old December 29th, 2015, 06:08 PM
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Unhappy Re: SO who came up with the GMC V6's???

Dave, after the tooling was shipped out were service parts manufactured at a different plant or do you think that was just the final end of the GMC V6. Evidently GMC must of stockpiled a good amount of parts, back in 1984 I looked into buying a new 432 V6 and it was available through the dealer.
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