(first posted 6/30/2012) It’s beginning to sound like a broken record, but the years 1960-1961 were undoubtedly GM’s most creative and adventuresome ever: rear-engine Corvair; aluminum V8, the Tempest with half-a-V8 four and swing axles, the Buick 90° (three-quarters-V8) V6, Greenbrier van and Rampside Corvair. And there was another: the GMC truck V6 engine, which appeared in 1960. And unlike the Buick V6, this was a proper one indeed: 60 degree cylinder angle for even firing pulses, and a compact block assuring a short and stiff crankshaft. It was quite the bombshell; never mind its V12 “twin-six” version (post here).
Why a V6? Good question. To be different, for its own sake? Possibly, but not likely. And why not a V8? Hmm. Let’s look at the historical context, and perhaps a good answer will formulate.
GMC was famous for their truck in-line sixes; well, actually, that’s all they ever built, as gas engines. It was a venerable line, starting in 1939, when GMC stopped using the Pontiac six. The primary family included displacements that varied from 228 inch³ to the legendary 302.
270 inch GMC sixes powered the legendary “Deuce and a half” Jimmy 6×6 military trucks and other equipment in WW2, of which some 800k were built. Take that! We drove one and posted that here, with video.
These rugged ohv engines also were popular with the hot rod set in the late forties and early fifties, because of their big cubes (270 and 302), overhead valves and ultra-tough construction.
There was also a “large-block” GMC inline six, with 426 and 503 cubic inches, for the really big rigs and buses.
Given that a six cylinder intrinsically has a torque advantage over a comparable-sized V8 (all other things being equal), staying with that proven number of cylinders makes gobs of torque sense, for true truck engines. There’s a reason why literally every semi on the road has a six under its big hood.
And it was the era for GM to feel modern, so why not go all out and design the very model of a modern six? The 60 degree cylinder angle is of course the preferred one, since it affords an even firing interval of 120 degrees if a split journal crankshaft is used, as had been the case since Lancia’s V6 since 1950. In cross-section, it looks somewhat similar to the little Chevy 60º V6, eh? Well, the block is a bit deeper and beefier.
The GMC V6 was designed for serious truck duty, and came in a range of displacements from 305 inches³ to 478 inches³. Oddly, there was even a V8 version with 637 cubic inches, with twin balance shafts to compensate for its uneven-firing and vibrations, due to its odd 60° block. They were all relatively low-rpm engines, with some versions producing their maximum power below 3000 rpm. The M “Magnum” series that appeared in the mid-sixties had bigger ports and valves, and less constricted exhaust headers, and are the most powerful and desirable of the family.
I drove a GMC V6-powered medium truck, for an interstate sign erector outfit, and its characteristics were distinctive, in relation to the other trucks in the fleet. Its low-end torque put the typical Chevy small-block to shame, and was palpably better than the Ford FE-powered ones. It bit hard right from idle, and its characteristic sound was of course unique. We’re used to the slightly-tense grumble from the Chevy 60° V6, and the GMC V6 shared some of that, but through a megaphone. At full chat through some shorty pipes, it was memorable; more so than its actual power output, which was hum-drum.
It was America’s love for big V8s in their pickups that killed the GMC V6 in that role. As GMC started offering more Chevy V8 power, the V6 was relegated to entry-level duty, and eventually disappeared. In truck applications, it soldiered along until 1978, eventually also replaced by the growing appetite for diesels, or the big-block Chevy V8, which was undoubtedly cheaper to build.
The GMC V6 was also built in a diesel version, the Toro-Flow, as a cheaper alternative to the “Million-miler” Detroit Diesel 6-71. Probably the less said, the better. It had a spotty reputation, and I doubt anyone ever racked up a million miles on one. Many were eventually replaced with gas V6s or something else.
Some folks did put them in their GMC pickup trucks, like this one installed in 1967 in a then-new GMC pickup. They did better in less-demanding applications.
The gas 305 was the standard engine for pickups, and most likely is what thrums under the hood of this fine old veteran. Rated at some 135 or 140 hp, this was designed to be a blend of six-cylinder economy and V8 power, although some early complaints had those qualities switched around.
Which may help explain the mystery of the Scotch plaid valve covers some of these engines had. This picture is from the web site 6066gmcguy.org, which offers two alternative theories as to why a number of these motors sported them. What did I say about GM feeling adventuresome?
This particular truck first caught my eye when we moved here in 1993, sitting a couple of blocks down the street from us. It’s right up my alley, as you undoubtedly know by now. And it’s obviously got a granny-low fours speed, with a stick a yard long. Plenty of elbow torque to make sure it gets into the next gear.
This one sports a “Custom Cab”, the Brougham version of upgrade in the still-spartan early sixties. Mainly chrome, on the grille, bumpers and some trim. And that luxurious color-keyed arm-rest, on the interior. It was the way to distinguish a hard-core work truck from a soft-core work truck.
What really makes this truck exceptional is its original aluminum canopy. It and the truck have weathered the decades so gently.
That also explains the non-rotted out boards in the bed. Have they ever felt sunshine or rain? Maybe not.
The manufacturer’s plate is still there, and I had to do a double take when I first read it. I assumed there was another name ahead of MFG. INC, as in NIEDERMEYER MFG. INC. What was it, and why was it missing? Then I realized it was “GEM MFG”. Duh! A long-time maker of high quality pickup toppers. And from Portland too, which confirms this to be a “native”.
Always wished my truck had a nice big bumper like this. They were optional; trucks back then came without rear bumpers unless you wanted one. And this is the one to want.
Our walk-around is at an end. This truck went up for sale shortly after I shot it, and naturally, I was tempted. But what was I going to do with another old truck? A young guy bought it, and I saw it in another part of town for a while, and then it disappeared, for good. Hopefully, it’s being kept in a way so it will be around for another fifty years. It deserves it.
Neat truck, and interesting about the V6s. I bet it sounded great! I read somewhere once that engines with multiples of three cylinders all sound similar at speed. Not so sure about that – never could get my Buick 3.8l (90°) powered Vega to sound like it had a V12!
My Dad bought a new ’66 GMC 1/2 ton lwb fleetside with the 305 and 3 on the tree. He pulled our 20′ gooseneck cattle trailer with it and he explained torque to this 14 year old, The truck wasn’t very fast but it had a ton of torque. Your comment about the way it must have sounded is spot on! That’s something I will always remember. It made what I call a boogity, boogity boogity sound that was music to my ears. I am currently in search of a similar truck and am frustrated by the fact that most of the ones I find have been repowered with a V8. Oh yeah, those V8’s sound good but they will never give me that boogity, boogity boogity sound I’m looking for.
Hey Jerry, I’ve been a Master Tech for 40+ years and the first 305 V6 I heard of, I saw yesterday. Surprised the hell out of me. Anyway, the owner is a respectable young guy, in Escondido Ca. Wants to sell it. Granny 4 speed and all. Looks to be mostly original.
Ed — (writing in 2024). I had a ‘Cosworth’ Vega and was tempted to put a Buick in it, as we had for my ’54 Healy. Would you believe? 60mph in 1st, and the hood stayed elevated at speed! I am still trying to understand how the V-6 was made to run smooth.
My friend’s dad used to have a ’68 GMC milk truck that had been converted into a camper. It had a 4 speed stick like the one in that truck, and maybe the same V6 under the hood. I never had the opportunity to check, though it would have been funny if it had the same plaid valve covers. We took a few trips in it and always had a good time. I like the old GM trucks from the ’60’s. A dream of mine is to own a vehicle from the year I was born (1963, by coincidence) and a truck like that would be a prime candidate…or maybe a ’63 Grand Prix in black
Ok why does a 6 inherently have more torque than a V8?
For an equivalent-displacement engine, fewer cylinders of larger displacement each, so that the individual power impulses are larger? Maybe it’s that simple.
So maybe what you really want for a truck is a 300-cubic-inch, two-cylinder with massive pistons… 😀
The old 830 John Deere Diesel tractors had around 470 Cu.Inches in two cylinders. 16:1 compression ratio. Bore/Stroke:6.125 x 8.00 inches. Each cylinder displacement was 1 gallon.
Imagine driving a two liter four and a two liter V12. Or even a two liter six.
The relatively larger cylinders have their torque peak at much lower rpm, which is where they’re most useful in most normal driving, and especially so for truck and agricultural use.
Note: I didn’t say “more torque”; but “torque advantage”, as in more torque at lower engine speeds. Many variables determine any given engine’s maximum torque; too many to go into here. And modern variable valve timing schemes make that even more complex. But the general rule of fewer larger cylinders having a lower (and fatter) torque band still mostly holds.
How about a Colombo designed Ferrari V-12 in the first 1.5 L version?
Torque? What for you want torque? I give you revs – go use them!
There are enough serious techs around here to give a detailed answer, but I can take a stab at it. My understanding is that torque output is affected by the mass of the piston/rod/crank assembly, as well as the distance that a piston travels.
All things being equal, 6 big pistons with a long stroke will make more torque at a lower rpm than 8 smaller pistons with the shorter stroke of the conventional post-1949 American car V8.
I’m sure somebody has a chart comparing the torque curves of, say, the beloved 300 I-6 used in Ford trucks to a comparably tuned 302 V8.
Also look at what happened when the high-compression V8s of the ’60s were detuned in the ’70s. Horsepower fell drastically, torque not so much, because mass and stroke hadn’t changed.
Doh! Paul beat me to it.
“Many variables determine any given engine’s maximum torque; too many to go into here.”
I do think that it’s worth noting that stroke is an important one of those variables. A long stroke V8 would be harder to fit under the hood than a big 6, among other considerations.
Got it, the key is engines of equal displacement. Thus, a 300 ci 4-banger would have an even greater advantage.
I guess this helps to explain why so many big rigs run with 6 cylinder diesels instead of 8s, 12s or 16s…
Another consideration is that the inline six is inherently better balanced than a I-4, a V-6, or a V-8.
Engine smoothness is, for the most part, inversely proportional to the swept area of each individual cylinder (that is, really big cylinders tend to be rougher running). Add to that any primary, secondary, or tertiary shaking forces from the engine configuration and firing order and a big four or even a really big V-8 can become a pretty rough cob. Big straight six truck engines are not Lexus smooth, but I suspect if you made an inline four of the same displacement (particularly one tuned for off-idle torque like most truck-bound engines) it would be a lot like a cement mixer.
True, but a mitigating factor in large truck, agricultural and industrial four cylinder engines is the fact that they tend to run at low rpm. I spent many long days behind the wheel of a 264 cubic inch Farmall Super M-TA four cylinder, and it was a bit buzzy at the very top of its rated range (1450 rpm), but really not bad at all. In Europe, large four cylinder truck engines were quite common. And some in the US too; Hall-Scott made a big OHC four that was used in International trucks in the twenties, as well as as other applications.
Now what I really wonder is what an Offy 270 inch four felt like at 7000 rpm?
The two chief advantages of the inline 6 in big trucks is packaging and greater cooling area of the engine block itself. There is no advantage in HP or torque of the inline 6, everything else being equal.
Scandia has several V8 diesels in large over the road trucks. Their largest puts out over 100 more horsepower than the largest available Cummins, Detroit, Mack or Cat diesels here.
A 6 cylinder DOES NOT “inherently have more torque than a V8”. This is an old urban legend that has no basis in fact.
Engine power (measured in horse power) is a function of torque and RPM. Everything else being equal, engine power is dependent upon three things. They are displacement, BMEP (brake mean effective pressure) and RPM. Torque is dependent upon two of those things. Displacement and BMEP. For two engines of equal displacement and BMEP, torque would be equal. The number or the arrangement of cylinders does not matter.
That being said, in many (if not most) cases, 6 cylinder engines tended to have lower peak torque RPM’s than V8’s. This is where most of the confusion started.
Torque peak RPM (the RPM where peak torque is achieved) is dependent mostly upon intake valve event timing. Six cylinder engines almost always had cams with less intake event timing than V8’s. With smaller displacement, single or small two barrel carburetor’s, and single exhaust, breathing was limited, so a mild cam worked well and produced good low speed torque.
V8’s generally had more intake event duration, larger carbs and better flowing exhausts. Those items work well together with greater airflow so horsepower is generally greater. Torque peak RPM is almost always at a higher RPM due to the greater intake event timing.
Well, that’s not always the case.
If I have 200 cu.in. inline 6 and a 400 cu.in. V8, the V8’s gonna win the torque contest every time.
However, in relatively like displaced engines, the reason is usually that the rotating mass tends to be heavier with the inline 6.
Engine power isn’t just made in the combustion chamber, its also a factor of the physical weight of the parts and the leverage of the longer throw of a larger crankshaft.
Take for instance a Ford…..you can have a V8 of 302 cu.in., or an inline 6 of 300 cu.in.
The bore is the same size with both engines, but the 300’s crankshaft has a 3.98″ stroke, compared to the 302’s 3″ stroke crankshaft.
This means, not only is the 300’s crankshaft heavier because its longer, it also has a longer stroke, giving added leverage for which the engine can use to do work.
These all combine into an inline engine usually possessing more torque than its V8 counterpart.
My great-grandfather had a ’69 GMC in this shade of green, with the V6 and three-on-the-tree. He (and eventually my spinster great aunt) kept it long enough that I eventually got to drive it, in about 1986. Great basic truck and fun to drive–and a stepside, my favorite pickup configuration.
Interesting info, and reminds you of a time when there was a compelling reason to choose a GMC over a Chevy other than styling.
I remember reading that the GMC V-6s also had a small pan running lengthwise under the camshaft which held a small amount of engine oil (and perhaps sludge). The purpose was to lubricate the camshaft and lifters during start-up. This was another small innovation that separated GMC from Chevy.
My Dad had a 1967ish GMC 4×4 with this engine. He worked for the USAF as a civilian and was reassigned temporarily to Texas. He towed our 18′ travel trailer from Florida to Texas and back for that assignment. Somewhere I have a picture of the truck and trailer at a campground with 2 feet of snow on the ground. I remember he brought me a pair of cowboy boots back from that trip. Just the other day we were talking about what a workhorse he considered that truck to be. He did say it was hard on gas. I’ll have to share this story with him. After having probably 20 or more trucks in his lifetime, just this week we sold his 2005 Ranger Edge (37000 miles) as he can no longer drive. I think it was harder for me than it was for him. It’s tough to see your ex Marine father who is your hero loose the ability to drive.
On a happy note, happy 4th all!
“ex Marine”
He’s a former Marine. Semper Fi to your father.
Had a friend with one of these who used to live in it (with a slide in camper) at the submarine piers in New London whenever we would be in port. More comfortable than the boat (think mid sixties diesel boats). He used to drive to his home in Maine when we had long enough periods off. Don’t know the size but it was a v6. I thought he said it was a 327 but now I think I am remembering wrong. He sure liked it but as said above, it was hard on gas.
When I was younger v8’s were important. As I got older and appreciated trucks more, I realized that v8’s are the sizzle and sixes are the steak. Last a long time and work good.
Just saw a 1981 AMC 258 yesterday. Stopped and talked to the driver because it was so much like the one I had. Still trucking from way back then. Can’t complain though. My truck has a 4.3 and I doubt you could talk me into trading it for a v8.
“When I was younger v8′s were important. As I got older and appreciated trucks more, I realized that v8′s are the sizzle and sixes are the steak. Last a long time and work good.”
I’m with you 100% on that. I passed on a few fine trucks when I was younger because they had a Six. Now it’s the dead opposite!
One of my favorite engines of all time!
I remember cruising the “Tradin Times” as a kid (when it was still on paper) and seeing several GMC rigs advertised as a 305 V6. I always chalked it up to it being a typo until later when I got to see and drive a stake bed with a 305 at a friends Farm/Campground.
Paul is right about the sound too. Like a Screaming Jimmy, you never forget it!
Interesting note, Most of the “Big Six” line didn’t run a Harmonic Balancer since they weren’t designed to run up to the speeds that most gas engines at the time did.
Yup me too. The buff books never taled about workhorse truck engines like this. They talked a lot about 427 sidewinders, hemis, Clevelands, 6-packs, etc. so I never knew either that most of the trucks and buses in the 60s and 70s were running 6 cylinders. As a little kid, I remember the 466 badges on the GMC school buses, just assumed it was a V8.
Inline Six cylinder engines do not need a harmonic balancer, and neither do inline fours…
Really? My I4 has an H.B.
Every Holden L6 has a balancer. I’ve replaced plenty.
Back in the 80s, my farming brother in law’s family had a 62-ish GMC grain truck that still saw regular service. I drove it once. It had one of the V6s and that long-throw 4 speed. That was my first exposure to the old V6 GMCs. You are right – it had a unique sound and a bunch of low to midrange torque.
I will also echo wstarving about an increasing appreciation of sixes. When I had a 63 F100, I was genuinely disappointed that it had the six instead of a V8. Only later did I learn that not only was the six of that era much more durable than the Y block V8, it was also preferable in the way it matched its torque/power with the way a truck needed it.
I also love the style of this truck. You don’t often see the pre-1964 version with the wraparound windshield. I am not a GM truck guy, but I seem to recall that these used some sort of torsion bar suspension setup that was either troublesome or is a problem getting parts for. Any truth to this?
The torsion bar suspension was used on the large/medium Chevrolet and GMC trucks, another GM bold experiment, to bring ifs to big trucks. It was a failure, and only used for a couple of years, starting with the new design in 1959. Look closely at the picture below, and it’s apparent. I used to get a kick out of seeing them, but it’s been years now.
Used in pickups as well, and it was by no means a failure but Gm was forced to cease using it by Chrysler. I still have a 62 C60 with torsion bar suspension and it can’t be beat for running across rough fields. Very smooth. Just can’t get parts for the big trucks anymore. I believe you still can for pickups.
When I was a little kid our neighbor across the street had a ’63 4X4 Suburban with the 305 V6 hooked to glasspacks and dual exhausts, I’ll never forget that sound.
For some reason I don’t think this engine was marketed in Canada. Most GMCs from this era that I’ve seen had Chevy engines in them. There were a few around but it was a rare bird in these parts. If I’m not mistaken the Canadian GMCs also used whatever suspension setup Chevy was using that year. They were essentially the same truck even way back then. I’m not sure why GM did this, it looks like the US models offered a real alternative to truck customers.
Nice old truck.
I can’t say it for a fact; but since Canada required extreme duties on any car imported from the States; and since GM did most of the Canadian manufacture on location, as it were…and since the pickup market was small in those times and the Canadian market also small…I’d be willing to bet you got a Jimrolet pickup, a truck cobbled together with parts from both Chevy and GMC lines.
Since they were mostly similar, it would be even harder to tell than with other GM-Canada kit-bashing. But the frames and drivetrains WERE different; and the instrument panels also. Since the Chevy engine was already there…the Jimrolet pickups got the Chevy power. Take that, Canukistan! Try and slap duties on our trucks, will you? You get a Biscayne engine in your work trucks!
I have a French language brochure which I presume is Canadian, and it mentions this engine.
My uncle bought a new 66 GMC stepside, after his 61 Apache 10 had been run into. The GMC was a pretty truck, a light blue and white 2 tone. A very cheap vehicle, having no options except the v-6. I figure it was a special order and the guy who ordered it didn’t buy it. Or as equally possible, my uncle bought it before they contacted the order guy. That happened to my Dad. When my Dad ordered his 72 Polara, a month or so later, he saw his identical car with the same dealer sticker on it. He got his car a month after that. So there were two identical 72 Dodge Polaras in our county.
Anyhow, my uncle’s car had 3 on the tree, painted bumpers and no options. It didn’t even have a passenger sun visor. I recall him installing the 61’s radio in the 66. But the 2 tone really gave the truck class. When my uncle died in 1976, my Dad took the truck over. It was in poor condition, really rotted out. I drove it a few times, it had holes even in the floorboard. My Dad sold the truck for $ 150 to a guy who did a fair job of restoring it. I still saw the truck into the 1980’s. I wouldn’t mind having that truck today.
The plaid valve covers were because the GMC V6 was called the “Scottsman Six” for its thriftyness, i.e cheap on gas and low operating costs. Of course that dates back to the Mad Men era of marketing lingo, when you used to be able to say things like that in ad copy, can you imagine that today? The 2013 Chevy Malibu with our new “Oriental Smart” engine management system!
I miss the days of GMC being an actual truck company, with a full range of trucks from light duty pick ups to full on semi trucks and interstate coaches, instead of a truck line up for Buick dealers.
I want one of these so bad… anything with the huge displacement V6 will do, but I especially like the early ones with the goofy eyebrow turn signals like this ’63.
Was the Toro-Flow available from the factory in the smaller pickups, or is that ’67 picture shown up above an engine swap? I’m surprised even ONE of those is still around. Really nice job with this and the Twin-Six article, they’re some of my favorite daydream topics.
Toro-Flow was a swap; they were never listed for anything but the medium-sized and larger trucks. There really wasn’t a market for diesel pickups then. They cost more, and gas was cheap. Plus, they didn’t make a lot of horsepower, without turbos.
That’s what I figured, but you threw me off with that picture and the wording – looks like it could have come down the assembly line that way.
The fantastic 6066gmcguy.org site shows a 478 V6 twin turbo with a factory engine code, but I bet that was an aftermarket setup that may or may not have been a dealer installed option. From looking at the figures posted there, the diesels probably would have been a good fit for the regular pickups… but like you said, they didn’t make a whole lot of sense in the mid-60’s, and they probably didn’t even get much better mileage than their gas counterparts. Compared to the Detroit Diesel stuff in the heavy rigs, they were utterly pointless! Still cool that they built them, though…
The military bus/ambulances with Superior bodies used a twin turbo Toro-Flow 478. It was the only application to do so.
I believe there were also some twin turbo marine 478 Toro-flows with the water cooled manifolds.
I have a 1969 GMC 1500-3500 owners manual, and the 305V6 is listed in the specs pages
I should have known it would be a gas engine, but a friend sent me a video of a 1960s GMC heavy haulage tow truck with a 2-stroke V6 diesel going for a short drive. There is a tag line about the number of gear changes for the number of miles or minutes – way more changes than miles/minutes of course – and it is a twin-stick setup which makes things trickier. Anyway the sound of the 2-stroke diesel is something else, not much muffler involved either. One of the other files was sound-only of a Gardner 8cyl supercharged diesel, so you have the whine of the blower & gearbox also – incredible.
Well John, I’m willing to bet that several members of your submarine force could find a video of a two stroke diesel with a blower that is even louder. Try youtube and one of ours that is a museum boat somewhere just fired off a 248AS that fits that bill.
Nice. Very, very nice.
I’d say the plaid valve covers were for a Chevy Scottsdale, but I suppose not. No clue.
May have missed prior mention but if not noted yet; Vietnam campaign ribbon decal on back of camper shell or topper, depending upon the nomenclature utilized in your domicile area.
My best friend once had the standard long bed version of this truck, though his was a ’62 that he bought used in the late 90’s. Originally bought, it was primered and had a cheap cassette deck that had been installed later in its life that didn’t work, thanks to a battery hookup mishap with the previous owner. The big thing he did was have it shot with an inexpensive coat of Aqua blue paint at I think Earl Sheib or Macco. The truck, unfortunately came with more modern GM dog dish hubcaps from a later truck or van though.
The guy hooked it up backwards and it fried the internal electronics so there was no working sound system in it, but a portable boombox did the trick on the cheap for tunes.
I can’t recall if it had the V6 or the V8, but it did have the 3 on the tree with funky shifter linkage that he swapped it out for a floor shifter to make it easier to drive.
I think it only stranded him once when it developed an electrical charging issue that fried the battery by over charging it. I don’t know what exactly what caused it, but it was NOT the voltage regulator, that much I do know. It left us stranded one day on an outing up the Chinook Pass byway, aka State Route 410 up through Chinook Pass in the Cascades back in the summer of 1997.
I want one of these V6-equipped trucks so bad. GMCguys’s site got me hooked on these engines.. The next time a heavy duty truck with one of these comes across the scales at the scrapyard, I’m pulling the engine. I’ll make room for it somewhere.
Thanks for giving this engine some deserved exposure! I hope it’s okay if I post this link but it’s very interesting, especially if you like these old school engines:
http://www.ford-trucks.com/forums/447226-534-vs-everyone-else.html
We have an old GMC 4000 COE grain truck with a V6 Toro Flow diesel that has been on our farm since 1971. I think it is a 1966 or 1967 model. Dad never had to worry abotu me getting a speeding ticket on the way to the grain elevator in that thing because it WILL NOT run faster than 55 MPH with the accelerator all the way to the floor because it is so underpowered with that Toro Flow. Apparenly the Toro Flow had such a bad reputation for being a puny engine and oil leaks (mechanics called it a “terrible flow”) that nobody wanted them which is why my dad got a bargain from the dealer when he bought it slightly used back in ’71. It has a few dents and needs a paint job BAD but is still hauling grain.
The canopy is 26 guage steel not aluminum, it is manufactured by gem top, the logo seems to be faded quite a bit. I can’t imagine anyone not recognizing this logo. They still make gem tops but they are just junk compared to what is on this truck. These V6 engines were very good but they were far from econimical. I have never seen a canadian GMC with a real GMC engine.
My dad had four GMC’s with V-6’s to my knowledge. He purchased a brand new 1960 2 Ton truck with a V-6 and 16 ft farm bed, and a 4 & 2 transmission. She’d walk the dog, right up to about 55 mph carrying 20,000 lbs.in the bed. I’ll never forget the sound of that V-6 while going thru all 8 gears, it was a pretty sound. While he owned it he purchased a used GMC 1/2 ton pickup with a V-6 and automatic tranny. It wasn’t around long when he traded it for a new 1963 GMC 3/4 ton pickup with a V-6 with a four speed transmission, and a low speed rear end. It pulled a 16 ft stock trailer right along, up to about 60 mph. It was traded for a new 1967 GMC 3/4 ton with a V-6 and an automatic transmission. It was a little “doggier” but would lean into it until you hit about 70 mph pullin’ a 16 ft stock trailer. The three he purchased new never had any engine problems. The one he purchased used did have engine problems. That is most probably why it was traded off in the first place.
Hi, New to the froum.
I owner one of these engine restored and mated to a 4 speed htdramatic for the 1960 GMC. The bed is getting painted and the truck will be complete hoping to make Crusin’ the Coastin October ’13.
I fell in lover with this truck when I saw the first one in 2000 and bought it, had the truck in the paint booth with Katrina hit. Lost everyhthing including the dog, had to start all over again.
The engine is rebuilt and speced in ready to go.
Cool motor…Is the rig finished? Any pics you can share? I have a 1960 GMC 3500 dually flat bed.
My turn! My mom bought a 1956 maroon and white Chevy wagon when our Desoto died in Alabama. I was 2. The old man got mad cuz he wanted to buy the first new car-waited a year and bought a 2-door ’57 Chevy, white top, black bottom, silver fins, six cyl, post, 3 on the tree. Traded that in 1963 on a brand new leftover 1962 GMC Carryall, with the 305 V-6. Got about 300,000 out of it(the speedo broke at 270,000)
I bought a 1964 GMC, 3 speed 305 of my own. In 11 years I put into that truck:2 engines(plaid valve covers on 1), (8) 3-sp trannies and (2) 4 speed trannies(alone!). 4-5 clutches, 2 rear ends, a windshield, hood hinges, and lots of other work! One rear end blew up and took out clutch, and tranny. The ’62 my Dad bought had torsion bar suspension as did my ’62 flatbed dumptruck. That had a 5 speed, with a 2 speed Posi-Trac rear end. It was faster than some taxis I had driven! That engine was a 351 V-6.
MANY GMC and Chevy 3 speed column shift had the shifters jam-esp going from 1st to 2nd. I have seen guys replace trannies trying to fix this-all you have to do is remove the steering wheel and with a can of WD-40 drench the two thin tubes which have dust and grease hardened on them. This should work 2-3 years and then needs repeating. The hood hinges are somewhat weak, and the body supports near the radiator rust so look for that. If the heater controls are all there it’s had a good life-almost all have broken. The one thing that stymied me forever was: what color is the interior paint-its kinda green-grey-brown without being any of them!
Please someone have photos or videos of GMC engines big-block six-cylinder in-line (426 or 503) inches? And also using data from a car blocks the GMC six-cylinder in-line (426 or 503)?
My friend has a GMC 4000, V6, and we believe its a 1961. 4gears with a high and low for each. it fires up and runs good, ease the choke out until it idles well. Battery is totally dead. The problem I am running into is that it keeps dying on my as we drive it. Usually when shifting into third-low. Fourth low seems to work ok though. any advice at all. I just picked up a new battery- 750 cca, hoping this will help. it seems that the idle is the real problem though- engine cleaner?
the GMC 4000 I am referring to looks just like the one with the photo of the cement truck on the back, except ours is used to haul a water tank on a ranch.
My Dad had a ’64 GMC 3/4 ton 4×4 It was solid red with a tow-truck style front bumper with a 3 speed on the column. It was a REAL truck of course it rode like one too. We used it for everything, general farm truck, snow plow truck & with a slide-in camper. Ours even had the horrible split rim wheels. It was kind of a hoot watching my Mom drive that truck, because as said above it was a TRUCK. The other thing that was funny about this series of trucks was a friend of my fathers was riding in the passenger seat and fell asleep and nearly fell out going down the highway because of the way the inside door handles worked.
That looks like a GEM TOP logo. My uncle had one on his early 60’s Chevy pickup when I was a kid. I think the red “GEM” has faded fron the logo.
just traded a boat for this beauty! 90k original miles
Picking up a 65 GMC dump bed 4×4 v-6 farm truck w/44.000 miles from Idaho this weekend sight unseen can’t wait to see what I get! I’m a ford guy but could not pass this up. I like old stuff. Hasn’t run for 18 years been in a barn but 1k I’ll take a chance
I have a Toro-Flow II DH-478 in my bus. It’s a 1971 GMC TDH-3301 New Look. It still runs well.
These small New Look buses were produced in very limited numbers – only 510 were ever made, and they were considered a light duty bus.
The GMC 305 and 351 V6’s were also used in the GMC mefium duty and school bus platforms…..The school district that I went to school in bought nothing but GMC’s from the early 60’s through the mid 1970’s….Up to 1969, they bought them wirh 305’s and 5 speeds…..From 1970, the buses were spec’d with 351 V6’s and 5 speeds with the newest ones having the 4 speed Allison automatics.
They definitely had a unique sound to them but were a bit underpowered for the weight they had to carry…..especially when filled with 40 or 50 kids.
I remember the drivers needing to rev the engines up to against the governor in each gear….otherwise on any sort of upgrade, the engine would fall flat on its face until the driver dropped it back down a gear or two.
I can even remember a new driver being trained on our bus route with a seasoned driver riding in the first passenger row…..We were riding in a 1973 GMC 6000 with the V6 and 5 speed…..The new driver was ‘short shifting’ it…..not,letting the revs build up too high before upshifting. The seasoned driver told the new driver that he needed to stay in the gears longer and that he did,not have to worry about over revving the engine because it had a governor on it that would prevent it from going over a certain rpm.
Love those motors. I had one in a ’60 8 ft step with dual glasspacks that blew out within a month. Fantastic sound especially when revved well above the 3000 mark. They were designed to work, huge water jackets (my 1/2 ton took 8 gallons to fill) valve rotators on both intake and exhaust,enormous in and out ports in the heads and so on. 10 mpg like clockwork loaded or not. I always wanted to build one with much higher than stock compression and a 4v carb.
The first GMC school bus I drove had that engine with a 4 speed , early 60s.
“The 60 degree cylinder angle is of course the preferred one, since it’s the only V6 configuration that gives even firing without split crank journals,”
60° V6s absolutely have split crankpins. Even more so than 90° V6s, such that 60° crankshafts are called a “flying pin” configuration.
for a four-stroke V6, you need a vee angle of 120° to eliminate the need for split/flying crankpins. But that would make the engine pretty wide.
_VERY_ good engines these and I don’t like ‘V’ configurations .
The plaid rocker boxes are always funny as these were thirsty beasts from new .
Nearly indestructible though .
The yellow cement truck is a ’60 ~ ’61 two year old rig .
-Nate
Clearly remember my dad’s 1960 gmc v6 4 speed posi. rear 2 w d long wide box fleet side, 11 mpg loaded or empty hauling scrap from Madras and sheet steel back from Portland climbing over Mount Hood in 3rd gear. was not fast but steady. After a stint in USMC worked for Deschutes ready mix who had a 6 cy mixer and interchangeable dump truck box on a 3 axel gmc truck v6 4 and 3 speed again steady not quick.
Howdy;
I owned a 1963 GMC Carry All 4×4 with the Big Block 305 V6, 4 speed (granny). The truck had the ‘plaid’ valve covers. It ran like a top, a real stump puller. The engine developed 375 ft lbs of torque at 1600 rpm. That full pull at 1600 rpm’s! The story I heard back in the day about the ‘plaid’ valve covers was that GMC would pull engines off the ‘line’ and tinker with them and blue print them before sending them back. Mine had 242K on it when I pulled the heads and they had less than 10 thousandth of wear. It was then bored out 10 thousandth to 315 cu in.
A fine vehicle for sure…
Just bought a 68 gmc from a junk yard with a 351 v6 150,000 miles been sitting for ten years filed the points dumped gas in the carb and fired right up purrs like a kitten I have lots of 67 to 72 chevys but I think this is my new favorite truck it’s a 4×4 3/4 ton grany 4 speed with 456 gears dually with diggers it’s bad ass! I heard you can use a electronic distributer from a Buick v6 is this true ?
Grew up spending summers w/ my grandparents on their farm in south Texas. My grandfather had a factory custom ’63 GMC 3/4 ton, 4×4, 305, V6 w/ a wench on the front, and rear PTO, 511 front and rear end, that he ordered new from RO Evans in Garland, Tx. I learned to drive in this vehicle and have too many great memories to recount here, but fast forward to Oct 2016. I’m sitting in my living room, watching a Meacum auto auction and pondered the fate of “the truck”. Got on my IPad and started googling it, down in central Texas. Miraculously, it popped up on Craig’s list, for sale for less than 24 hours. I immediately called the gentleman and couldn’t believe my good fortune, positively identifying our old farm truck. Picked it up a week later and trailered it home. Very fortunate that this gentleman kept everything original (w/ exception of the split rim wheels). It runs beautifully, everything works and has 73,800 original miles on it. It was on the farm all but the 6 years this gentleman owned it. I estimate it spent a good 25 years, in the barn down there quietly and gracefully aging, while I covered the globe in the Army. Divine intervention? I have to believe so! Very blessed to be reunited.
Additional picture:
Had a ’64 3,5 ton truck with the 305 V6, there’s no other V6 that sounded like that going up hill with a full load. Fitted with dual exhaust. It weighed 3,5 ton and carried 3,5 ton. All I have left of her are the V6 hood badges
Inherited my grandfathers 63 GMC with the 305 V6 that he bought brand new. Definitely has a unique sound (which is one of the most memorable aspects growing up going on joy rides with my grandfather) and is a total joy to drive now as an adult. Pic below, it is what I call ‘screaming green’, ha! I had the hubcaps off for cleaning at the time.
Great story and fabulous truck Wes! Love those wheels and looking for the same for mine to replace the steelies that were fitted to replace the original split-rim wheels, now outlawed in Tx & Ok. Tough to find white, 8 lug, 16in wheels. Ideally maybe I’ll run across the red on white hubcaps as well one day. Take care.
And today…all original w/ exception of the wheels.
I never noticed before today, but the V6 logon on the fender has a 90 degree angle. You would think GMC would have made it 60 degrees to match the engine.
Back when I was with an auto parts store, one of our 3 delivery trucks was a brand new GMC V-6 long bed. We delivered a lot of exhaust parts to service stations at the time since this was before the muffler chains had reached our area. Remember the unique sound. Never got to drive it though, since our senior driver was very reliable. They used me as a substitute driver and I was relegated to a ’63 Chevy wagon or a ’60 Dodge long bed. The brakes on the Dodge went nearly to the floor and the Chevy’s steering arm had been repair welded. Went back to working at the service station after a short time.
I’ve often wondered about the 60-degree V6.
The optimum V-angle for a V12 is 60 degrees: 720 / 12 = 60 (720 because a 4-stroke engine has 1 power stroke per 2 revolutions)
The optimum V-angle for a V8 is 90 degrees: 720 / 8 = 90
The optimum V-angle for a V6 should be 120 degrees: 720 / 6 = 120
There have been few 120-degree V6 engines. As far as I know, none is in production today. (It’s wide, but still narrower than a boxer engine)
I’ve searched online for photos of 60-degree V6 cranks. They all have 4 main bearing but 6 separate crank journals (2 split crank journals between main bearings) Not sure why a split-journal 60-deg V6 is more advantageous than a split-journal 90-deg V6 in this regard.
A V8 crank, on the other hand, has 5 mains and 4 crank journals, with connecting rods from both banks sharing one crank journal (as would be the case for a 120-deg V6 (4 mains, 3 journals) or 72-deg V10 (6 mains, 5 journals) or 60-deg V12 (7 mains, 6 journals) or 45-deg V16 (9 mains, 8 journals))
I believe the reason is the journals are split is to preserve an even-fire ignition system. If the conrod journals are not split it is an odd-fire, which requires a different dizzy setup. The Citroen SM I had for awhile (never got past project status) had common journals, and was an odd-fire. The ignition system was ten kinds of weird, with two separate points sets and a twin-circuit two carbon brush rotor and cap. The terminal towers were in 3 pairs of narrow angles. There was a fellow who came up with a pertronix-style setup that used two pickups on a custom plate (the system also used 2 coils) at ISTR a 30 degree angle.
I forgot to add the pointless system used a standard six-slot ‘chopper’ with 3 of the slots filled in.
The 60-degree V6s have always had split journals. If the they had common journals the shaking would be even worse than common-journal 90-degree V6’s since 60-degree is worse than 90-degree in terms of deviation from the ideal 120-degree. GM tried to get away with common-journal 90-degree V6s, it probably thought 90 is close enough to 120 but later had to make “even firing” split journal 90-degree V6s as well to quell the vibration. Except for being wider (but lower), 90-degree split-journal V6s are no worse than 60-degree split-journal V6s.
This body style GM truck seems really thin on the ground now. In fact I see more Advance Design trucks running around, some them still obviously working, than later ‘50’s and ‘60’s pickups, until the ‘67 and newer GM pickups. By contrast, there are still quite a few early- and mid-sixties Fords on the roads here. Due to sales numbers? Durability? Collectibility taking them off the roads and into museums or garages? I don’t know.
In middle school when I stated taking the bus to school, it was a GMC with the V6. I wonder which V6 full sized school buses had? I remember it had a 4 speed manual transmission, only once did the driver start off in first when we were stopped on a hill. Usually second was used from a stop. I think the driver would sometimes (or maybe all the time) would double clutch between first and second.
This was in the late 60s. One bus route used one of the GMC ‘old style’ rounded transit busses with the automatic that sounded like a 2 speed.
“Suspect is hatless, repeat, hatless!”
Some confusion is found in the description of this engine.
“60 degree cylinder angle for even firing pulses, and a compact block assuring a short and stiff crankshaft.”
Even firing is the result of coordination of crankshaft and block design. In this case, a 60 degree V6, most engine designers use flying webs to connect the two rod journals. Flying web crankshafts are longer than overlapping journal cranks and both are weaker than common rod journal cranks like that found in a V8, V12 etc. A longer crank usually means a longer block.
“The 60 degree cylinder angle is of course the preferred one, since it’s the only V6 configuration that gives even firing without split crank journals, something that hadn’t been invented yet, as the early Buick V6 painfully attests to.”
If you look at the cross sectional drawing of the engine titled “GMC’s V6 Engine,-TODAY’S MODERN TRUCK POWER” you can see the flying webs of the crank in between the rod journals in the illustration to the right. These are not overlapping journals of a 90 degree V because the journals would be too large to make it a good engineering choice. A 120 degree V such as the latest McClaren and Ferrari V6’s have common rod journals just like a 90 degree V8. The preference for 60 degree V6’s now mostly has to do with transverse front wheel drive applications. They may be better balanced than a 90 degree V6 as well.
The 90 degree Buick V6, derived from the 215 cubic inch aluminum V8, had odd fire due to budget issues, as in let’s not spend the money on a new crank design now, not because the flying web crank design had not been invented.
“Oddly, there was even a V8 version with 637 cubic inches, with twin balance shafts to compensate for its uneven-firing and vibrations, due to its odd 60° block.”
Yamaha designed a 60 degree V8 with Ford to fit inside the narrow engine bay of the 1996 SHO Taurus. This is similar to the 90 degree V10 Ford Triton and Chrysler V10 found in trucks and the Viper. The front of the engine is expensive to design and make. Spreading the costs over more units will reduce unit cost. This is almost certainly the reason for the separate heads of the Twin Six, an engine that would not see large, by GM standards, production volumes. Using the design and castings for both the Twin Six and the V6 would save money.
Thank you Oita Ikki, JZ78817, Bill and Ate Up With Motor for your clarity.
Thanks for pointing out that obvious error in the text. This was originally written back in 2009 at the other site, and I was a lot dumber then!
I’ve amended the text.
Hey Jerry, I’ve been a Master Tech for 40+ years and the first 305 V6 I heard of, I saw yesterday. Surprised the hell out of me. Anyway, the owner is a respectable young guy, in Escondido Ca. Wants to sell it. Granny 4 speed and all. Looks to be mostly original.
Back in middle school in the late 60s I rode on a GMC school bus. That’s what got me to become a manual transmission fanatic. I never realized it was actually a 4 speed on the floor until one day we were stopped on the hill leaving the school. The driver started in 1st, a very short gear with a distinct whine. He usually started in 2nd, and as noted elsewhere here typically ‘floored it’ with each gear up until 4th,
The bus had the V6 logo – and I wondered what displacement it was. Per Dave’s post in December 2015 it must have been the 351. I could identify the GMC V6 buses by the sound, in high school there were a couple of International buses that also had a distinct sound, I think those were V8s, In middle school one route had an ‘Old look’ GMC bus with the V6 diesel and what sounded like a 2 speed automatic transmission.
I assume being a truck engine, the 305 and 351 V6s may not have had balancing to reduce vibration like the 231 V6 used in cars of that era. Then again, I test drove a 1965 or so Buick Special in 1973 with the V6 and 3 speed manual on the column. At idle, definitely a noticeable vibration, Not so much with my friend’s ’74 Olds Starfire.