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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old December 24th, 2015, 04:12 AM
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Default SO who came up with the GMC V6's???

I've been deep into research on these v6's and wondering....what made GM come up with such a different engine? I mean...the thing makes a SBC look like a briggs and stratton. lol And its slower than a 292 I6 by far, but sure has a ton more lugging power. Mine pulls pretty darn good with the 4 barrel and split exhaust, but my 292 with the same mods pulled 10 times faster which makes me wonder....did GM purposely make these to be luggers? Shifting my 292 at 4000 RPM was no problem, but 3000 on this is scary. haha I'm NOT downing the V6's in Any way....just curious as to the engineering behind it. I mean....loaded down with manure I could pull hills at 55 with my 305 no problem and that was with a plugged up 2 barrel. Just thought it would be an interesting discussion. I love my BB V6 and wouldn't trade it for any SBC, but the thing interests me. lol
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Old December 24th, 2015, 03:07 PM
George Bongert George Bongert is offline
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Default Re: SO who came up with the GMC V6's???

Greetings TJ!

As to who at GM came up with the design of the big block V-6, well, that's information that I don't have, although I also would like to know who that person was. As to the comparison between the 292 I-6 and the various versions of the GMC Big Block V-6's, I'll take the Big Block V-6's any day of the week before I would take the 292 I-6. As many here know, I once owned a 1963 Chevy 30 Series (1 ton) pickup originally equipped with the 292 I-6 which I eventually replaced with a GMC 305 V-6. Now, there will be those here who will disagree with me, but my feeling is that the 292 I-6 was nothing more than a glorified car engine put in a truck, and not necessarily designed to be a truck engine, although GM engineers would differ with me on that point. I know, because my Dad and I had plenty of problems with the 292. When I replaced the 292 with the GMC 305 V-6, those problems all disappeared. Now, having said that, yes, the 292 would be faster on acceleration and rev higher than a BB V-6, but as you indicated, the GMC V-6 will outlug the 292 six ways from Sunday, and all in all is a much more durable engine than the 292 ever was or will ever be. I know you have several 292's in your collection, and that you are very pleased with them. My experience has been the 292 is an engine (along with a few other GM engines) that I do not strongly favor.

On a lighter note, Merry Christmas to all here in the 6066 GMC Truck Club!
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Old December 24th, 2015, 05:08 PM
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Default Re: SO who came up with the GMC V6's???

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

As to who at GM came up with the design of the big block V-6, well, that's information that I don't have, although I also would like to know who that person was. As to the comparison between the 292 I-6 and the various versions of the GMC Big Block V-6's, I'll take the Big Block V-6's any day of the week before I would take the 292 I-6. As many here know, I once owned a 1963 Chevy 30 Series (1 ton) pickup originally equipped with the 292 I-6 which I eventually replaced with a GMC 305 V-6. Now, there will be those here who will disagree with me, but my feeling is that the 292 I-6 was nothing more than a glorified car engine put in a truck, and not necessarily designed to be a truck engine, although GM engineers would differ with me on that point. I know, because my Dad and I had plenty of problems with the 292. When I replaced the 292 with the GMC 305 V-6, those problems all disappeared. Now, having said that, yes, the 292 would be faster on acceleration and rev higher than a BB V-6, but as you indicated, the GMC V-6 will outlug the 292 six ways from Sunday, and all in all is a much more durable engine than the 292 ever was or will ever be. I know you have several 292's in your collection, and that you are very pleased with them. My experience has been the 292 is an engine (along with a few other GM engines) that I do not strongly favor.

On a lighter note, Merry Christmas to all here in the 6066 GMC Truck Club!
Thanks for the reply! SO what problems did you have with the 292? The stock 292 that was in my C10 performed nicely even when towing, but I have now gone through and hotrodded it. lol So it doesn't count as a comparison anymore. But yes, I'm pleased with my 292's. But when I came across my GMC with the V6 I was even More pleased because I never had seen one in person before so I had to have it. lol I Love my V6 and like I mentioned...wouldn't trade it for a SBC or anything for that matter accept a bigger V6. But I'm interested to know what you didn't like about the 292's? GM engineers made the 230's and 250's to be more of a car engine and the 292 to be the truck engine of the bunch(not trying to start an argument). The 292 was made the truck engine because of how much taller the deck height was and the much longer stroke to get that added torque which for my experience in a light duty truck served nicely. But in a large C30 like you had that may have been a different story, but I can easily understand why you'd prefer the V6....they were made so bullet proof and durable its crazy. lol Merry Christmas to you to!
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1964 GMC 1500 305E/sm420 4 barrel intake mod and dual exhaust.
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Old December 24th, 2015, 06:02 PM
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Default Re: SO who came up with the GMC V6's???

So GMC was married to GM sister division Pontiac in the 40's and 50's and shared Pontiac's design team for engines. GMC used Pontiac car V8's from 55-57 before Pontiac designed GMC its own variation of the 1958 Pontiac 370 V8 which was a smaller bore 336 V8. In 1959 when Pontiac went to the famous 389 V8, they gave GMC another version of the 336 V8 which had a shorter stroke and was based on the 389 V8's bottom end. This version of the 336 was slightly faster in terms of horsepower over the previous years' 336. During these years, Pontiac engineers developed the V6 as a means of giving GMC its own engine that would give the trucks a distinction from Chevrolet and give them the powerful low end torque they are known today for. You can see the Pontiac engineering influence in the power steering pump and fuel pump designs and the way the V6 intake still sits up on top, separated from the push rod valley vs a Chevrolet fully enclosed design. Everything about the GMC V6 design and appearance screams Pontiac when you compare to the early V8's Pontiac shared with GMC. The V6's are the last stand from Pontiac before GM fully aligned GMC with Chevrolet by say 1966 or so and started offering Chevrolet engines in GMC's. By 1969, the V6 was over with, and the Chevrolet V8 won out over the V6 for cost and efficiency reasons and maybe other things like fuel economy. Not sure if this answers your question any but I believe this to be correct unless Pete, Ed or some of the more knowlegeable and experienced V6 users have anything to add that might shed any more light on the subject of who came up with the V6 design
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Old December 24th, 2015, 06:10 PM
bigblockv6 bigblockv6 is offline
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Default Re: SO who came up with the GMC V6's???

TJ, speaking of acceleration was there a noticeable improvement when you added the 4bbl? One of the drawbacks of the 305 is it has a poor power to weight ratio that's why I prefer the larger displacement V6's. The 305 shares the same block as the rest of the family of 60 degree V6 engines up to the 478, so that makes it really heavy for it's smaller displacement. If you would like to know more on the development of these engines go to Jolly's 6066 GMCguy website and check out the Sept 1959 issue of Popular Science. They actually tested a 1bbl 305 in a prototype 1959 Suburban, being that it was in a smaller and lighter truck the performance was more V8 like of that era.
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Old December 24th, 2015, 06:32 PM
bigblockv6 bigblockv6 is offline
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Default Re: SO who came up with the GMC V6's???

GMCNUT, for the most you are correct except for a few things. GMC was not married to Pontiac in the 40's & 50's nor did Pontiac engineers design the GMC V6. In the 50's since GMC didn't have their own V8 they chose the Pontiac V8 and of course the was an excellent choice since Pontiac had larger displacement engines, but the Pontiac V8 wasn't the only V8 GMC offered. Trucks that were larger than medium duty used Oldsmobile V8's because of their low end torque. With the introduction of the V6 that was GMC's remedy to be self sufficient by having their own powerplant, As bigger V8's came around the 305 definitely didn't cut it so the 351 was brought out in the light duty line in 1966, an improvement but demand was there for high horsepower V8's so in 67 they brought out the entire line of Chevrolet engines. That was GMC's downfall as it got much easier to produce trucks that were fully interchangeable with Chevrolet, too bad GMC didn't stick with the Pontiac V8's, It wasn't until around the mid 90's that GMC and Pontiac combined to be the same division and that lasted till 2010 when GM killed off Pontiac.
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Old December 24th, 2015, 07:22 PM
George Bongert George Bongert is offline
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Default Re: SO who came up with the GMC V6's???

Greetings again TJ, and everyone else in the Club!

As to why I disfavor the 292 I-6, I'll try to be as brief as possible. My Dad bought that '63 Chevy C-30 in 1966 with 42,000 miles on the odometer, and at that time with three new pistons in the engine. After putting on another 3,000 miles, he came home with the engine knocking like crazy. This was in 1968, and I was in high school at the time, taking an auto mechanics course, and I diagnosed the problem (correctly I might add) as being a rod bearing knock. We dropped the oil pan, and it didn't take long to determine that the # 1 rod bearing was totally pounded out. We ordered a new (not rebuilt) short block from our local Chevy dealer, and installed it in an unheated garage in 20 degree below zero weather. Now let me tell you that you only worked on it for about 15 minutes at a time, and then had to go in and get warmed up before continuing to work on it on and off until it was completed. Now, as to problems with the new short block, the engine ran pretty much quietly except for the fact as more miles were racked up, and by the time there was 10,000 miles on that new block, that 292 developed a serious case of piston slap. Remember me mentioning earlier that the original engine had 3 new pistons in it when my dad bought the truck with 42,000 miles on it? It didn't matter whether the engine was cold, or at operating temperature, you could hear every piston in that engine slapping merrily away. Dad turned the truck over to me, and when there was about 70,000 miles on that 292 replacement engine, I knew at some point the dam* thing was going to leave me stranded high and dry somewhere. A neighbor had a 1962 GMC 3/4 ton pickup that he had retired mostly due to the body being pretty rusty. I bought that truck and took the 305 BB V-6 out of it and put it in my '63 Chevy. Putting that BB V-6 in my truck was the best decision I ever made, because it was an engine that I could count on getting me from point A to point B and back without the worry that I was going to be hoofing it for help because of an engine failure. So now you know why I have little faith in the reliability of the 292 I-6 and why I think they are best suited for use in a light (1/2 ton) truck, or better yet, a car. That's why I called it a glorified car engine.
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Old December 24th, 2015, 07:40 PM
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Default Re: SO who came up with the GMC V6's???

All the Chevrolet engines whether small or bigblock V8 and sixes were nothing but passenger car engines. Chevrolet even converted the big block V8 into a truck engine by adding an extra compression ring to the pistons, adding an inch to the deck height and there the 366 and 427 trucks engines were born, truly over glorified passenger car engines and GMC was forced to drop their V6 for these junk piles in the mid 70's.
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Old December 24th, 2015, 09:11 PM
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Default Re: SO who came up with the GMC V6's???

Quote:
Originally Posted by bigblockv6 View Post
TJ, speaking of acceleration was there a noticeable improvement when you added the 4bbl? One of the drawbacks of the 305 is it has a poor power to weight ratio that's why I prefer the larger displacement V6's. The 305 shares the same block as the rest of the family of 60 degree V6 engines up to the 478, so that makes it really heavy for it's smaller displacement. If you would like to know more on the development of these engines go to Jolly's 6066 GMCguy website and check out the Sept 1959 issue of Popular Science. They actually tested a 1bbl 305 in a prototype 1959 Suburban, being that it was in a smaller and lighter truck the performance was more V8 like of that era.
Big improvement for sure...and that's with the 4 barrel mounted on a 4 to 2 adapter. It should help even more when I have the intake machined to directly fit the carb. The split exhaust made for a nice improvement as well. I'll check out the sight for that issue! Thanks!
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Old December 24th, 2015, 09:20 PM
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Default Re: SO who came up with the GMC V6's???

Quote:
Originally Posted by George Bongert View Post
Greetings again TJ, and everyone else in the Club!

As to why I disfavor the 292 I-6, I'll try to be as brief as possible. My Dad bought that '63 Chevy C-30 in 1966 with 42,000 miles on the odometer, and at that time with three new pistons in the engine. After putting on another 3,000 miles, he came home with the engine knocking like crazy. This was in 1968, and I was in high school at the time, taking an auto mechanics course, and I diagnosed the problem (correctly I might add) as being a rod bearing knock. We dropped the oil pan, and it didn't take long to determine that the # 1 rod bearing was totally pounded out. We ordered a new (not rebuilt) short block from our local Chevy dealer, and installed it in an unheated garage in 20 degree below zero weather. Now let me tell you that you only worked on it for about 15 minutes at a time, and then had to go in and get warmed up before continuing to work on it on and off until it was completed. Now, as to problems with the new short block, the engine ran pretty much quietly except for the fact as more miles were racked up, and by the time there was 10,000 miles on that new block, that 292 developed a serious case of piston slap. Remember me mentioning earlier that the original engine had 3 new pistons in it when my dad bought the truck with 42,000 miles on it? It didn't matter whether the engine was cold, or at operating temperature, you could hear every piston in that engine slapping merrily away. Dad turned the truck over to me, and when there was about 70,000 miles on that 292 replacement engine, I knew at some point the dam* thing was going to leave me stranded high and dry somewhere. A neighbor had a 1962 GMC 3/4 ton pickup that he had retired mostly due to the body being pretty rusty. I bought that truck and took the 305 BB V-6 out of it and put it in my '63 Chevy. Putting that BB V-6 in my truck was the best decision I ever made, because it was an engine that I could count on getting me from point A to point B and back without the worry that I was going to be hoofing it for help because of an engine failure. So now you know why I have little faith in the reliability of the 292 I-6 and why I think they are best suited for use in a light (1/2 ton) truck, or better yet, a car. That's why I called it a glorified car engine.
Man, you sure had some bad luck with that engine. Sorry to hear about that. I never had those problems with mine....at 147,000 and being 50 years old I was doing burnouts and reving my worn out 292 up to 5000 RPM. haha Never knocked and no piston slap, but after an extra 2000 miles put on it, it developed valve train problems. Had no power and would sputter on take off....then it would be fine.....valves were recessed in the head causing them to hang open. Also only had 95 psi in all cylinders and 5 psi oil pressure at idle, but it Never left me stranded anywhere....even with all the problems I encountered during my final drive...she still ran and then died in the driveway. I had to have the valves adjusted at .006 clearance just for it to run somewhat smoothly. lol So yeah, I haven't had quite the same issues, but for an old engine that had a 3600 rpm redline from the factory that could do 5000 rpm I'd say that was pretty good. haha But onto the V6 again, I've never had a smoother running 50 year old engine in my life. This thing never misses a beat! After giving this thing a full tune up and valve adjustment this motor gives me confidence while I'm on the road...which is a plus being that its 50 years old with almost 200,000 on it and only 5 psi lost in the cylinders. They're one heck of an engine. Only engine I have that could idle up a hill lugging down to 250 rpm.
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1964 Chevy C20 292/SM420
1966 Chevy C10 292 hotrod 6/TKO600
1977 Chevy C20 572 BBC/TH400
1984 Chevy C30 292/SM465

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