702 GMC V-12 powered '62 GMC 1-ton
 

Hope to start this project soon. Am starting to get the parts together. This project may never be finished, but would like to preserve one of these old motors while I have the opportunity. They discontinued production of them sometime in the mid-60's. Hope to use the '91 1ton crewcab as a foundation. All help and guidance will be appreciated.
Thanks in advance, Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

Wow! That's quite an engine! Is that an air compressor sitting on top of it in the drawing? Sorry don't know anything about them except that the look long. I guess maybe not any longer than a strait six? What did they come in?

Re: GMC V-12 powered '91 Chev crewcab
 

They were used in the bigger GMC Road trucks, firetrucks, etc. The motor in the stand was set up to power farm irrigation wells here in the plains. They are 2 351 v-6's on one block, shaft, and cam. They would run for years on irrigation wells. Fuel hogs, tho.
visit www.6066GMCguy.org It tells alot more about the engines. Give specs, weight, and all. That will explain the need for 1ton chassis.
My purpose is not for a hotrod, hope to gear it for not more than 70+-mph. Just want to let people see the old beast in running condition. The truck won't have any real useful purpose. 3-5mpg about all it will get.
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

maybe even 3-5gpm!

Re: GMC V-12 powered '91 Chev crewcab
 

About like a Chinook, Mike, they both got powwer & torque!!!
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

dry weight for the 702 = 1485 lbs!

Re: GMC V-12 powered '91 Chev crewcab
 

If it's going to be one-off, and it will, put the engine behind the cab. Radiator could be in the stock location, and coolant lines run to the engine. If the bed you use is cut and covered (a hard tonneau), it would surprise a few folks who saw nothing under the hood.

You can have some fun with this, huh?

Re: GMC V-12 powered '91 Chev crewcab
 

Neat idea: Let's all have some fun with this. My intentions now are to chop the cab firewall and floorboads to accomodate it. Just leave the truck as an ordinary work appearance on the outside. You guys ingenuity may take me in any direction. Will be asking opinions on type of bed to build or use later on. Will sure have to add some weight on the rear axle some how. Maybe have to add some airbags in the front coils, depending on how low the weight mashes the stock springs down. End result being a dependable, drivable old truck with focus on engine, not external.
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

and the tranny is?

Re: GMC V-12 powered '91 Chev crewcab
 

Preferrably an auto, but probably not doable. Max RPM is 2400, so will probably need a 5-sd over to get up to hiway speeds. Your idea sure has validity from a weight distribution stand point. Cut the cab back instead of firewall. Two back bucket instead of fronts. Also would reduce cab noise.
Everybody keep thinkin' and engineering----
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

and both are as big as a house! good luck with the build...

Re: GMC V-12 powered '91 Chev crewcab
 

Then,you could put a seat where the motor goes and ride people around like a surrey.
Have you checked "The King of Obsolete?"I think I found him from a link on the 60-66 guy`s site.
It`s two motors running as one.It seems appropriate to run brownie gears.That`s two trannies inline for alot of ratios.

Re: GMC V-12 powered '91 Chev crewcab
 

Tandem engines are/were very common on these wells, also. There's been about every type motor used, but they had to be two motors the same. Just a shaft from flywheel to crank inline. No tranny involved on the wells as pump was matched to a certain motor rpm by gear head ratio on the pump. Everything had to run at a constant pump shaft speed.
cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

The scoot the engine back idea sure has merit for weight distribution. Why not sit it all under the cab/w 4 bucket seats, radiator in stock location, elec. fans, and a big air tunnel from rad out the cab back for cooling? The cab is long enough to cover all the engine. There should be room to haul "stuff" under the hood on each side of the big air tunnel. That might leave room for an ordinary truck bed of some kind. That should have some shock effect when the hood was raised.
Thanks,
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

that will make for some WILD exhaust tones too. that system would be fun to fabricate--a challenge i'd like to tackle. too bad you weren't closer to the shop i work in.

Re: GMC V-12 powered '91 Chev crewcab
 

I would lengthen the front clip that would look cool to have the front stretched 3 feet or so and all that motor tucked in there.
Ed

Re: GMC V-12 powered '91 Chev crewcab
 

Gonna be one crazy ride....

Re: GMC V-12 powered '91 Chev crewcab
 

that thing is a beast, boy would it look good in my 36 international.....im going to run it fenderless if i ever get a frame........

Re: GMC V-12 powered '91 Chev crewcab
 

If the engine is mounted behind the cab, and mounted to my way of thinking, it would be low enough. What about using an automatic, like a hydramatic from a GMC Deuce and a half (early 50's)? Then, an Allison would probably be a better bet. Either way, an adapter is gonna be needed.

Re: GMC V-12 powered '91 Chev crewcab
 

#1: If the motor is too far back, will we get too light on front axle?

#2: An automatic would be great. Cost may be prohibitive. Military sources is good idea. I'd like to find a salvaged V-12 truck/w bell-housing, clutch, and tranny intact, but that's too good to be true.

#3: Son's suggestion for "show&tell". With the empty engine compartment, Put rat and squirrel cage in there hooked to a tiny craft generator and let it run a little light bulb. Should add some to the surprise factor. LOL!
Keep engineering, guys and
Thanks,
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

A 545 Allison off maybe an IH or Cummins motor should bolt right up to the SAE pattern. You'd probably have to engineer a way to bolt the TQ to your flywheel & maybe a bushing to center the snout in the crank. A friend has a IH S- series that originally had a 7.3 & 545. He blew the engine, and put in a DT466 out of a twin screw. It bolted right up to the tranny. Shift points are not quite right, but it works. Someone needs to do some valve body/ governor calibrating for him.

If you want a 13 speed, his is probably just sitting there. I think it's an LL model. About 250 rpm between shifts (IIRC), but no OD. First gear would be about .3 mph @ 1000 rpm. :lol:

Re: GMC V-12 powered '91 Chev crewcab
 

If the drive axle stays in the stock location for the frame, I don't think there is any way for the engine to be too far to the rear. I suppose that it, when coupled to a gearbox, will extend significantly into the rear seat area of the crew cab body. My guess is that seating in the rear will be on either side of the engine, which would have to be covered and well-insulated.....for heat and noise control. Imagine a Humvee, if you will.

You could disguise the cover by making it look like luggage....heck, even to the point that you could buy some derelict Samsonite at a Goodwill store to hack, slice and dice into the shape needed to cover that big air pump.

I'd keep the radiator under the hood. I suspect the overall effect will be of a ginormas mid-engined tractor.....a tractor that would look like a truck.

Put in a 10 or 13-speed....that'd work. But I'd go for the Allison.

Re: GMC V-12 powered '91 Chev crewcab
 

Thats awesome, have someone grind u a cam so you can raise the powerband a little maybe get 3500 out of it, you'll probably need the 13 speed to keep it in the powerband

Re: GMC V-12 powered '91 Chev crewcab
 

Stretched hood would be great and an eye-catcher. My reservations at this time is getting weight distributed so the truck will drive and handle right, However, we might just set the cab back, extend front clip. Any way we can keep shifting weight from front to rear. Another goal is not alter external appearance. We'll call her the "47-Present Chevy/GMC board Special". She'll probably end up uuugly! Not you guys fault, but mine in putting her together.
But engine will have new paint!!
All ideas are good,
Thanks
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

I'm not sure you could get it in that truck without modifying its outward appearance. Maybe so... but thats one long, heavy motor.

How about putting it in the bed, over the axle that can easily handle the 1500lbs it weighs, and then working out some sort of v-drive arrangement to get the power from the engine to the axle thats below it? That way the truck would look normal with this huge engine in the bed...that actually powers the truck.

Re: GMC V-12 powered '91 Chev crewcab
 

Use a strait axle or better yet(I love spending other`s money)use a 3500HD frame.Much easier and heavier being a strait rail frame.I`m sure you could mount your crewcab on fairly easily.Check my avatar for a stretched nose big Chevy.It`s a puller that runs the V12 Detroit.

Re: GMC V-12 powered '91 Chev crewcab
 

That makes my gasser look like a pup!
When you drop the clutch on that, one of three things is going to happen: Wheels spin, something breaks, or things are gonna' mooove. I'm bettin' on the latter!
Heavier frame and axle would solve alot of things, but I'm holding on to keeping the innocent old, ratty 1ton look as long as I can, but I'm sure lots of changes will be made before this thing moves, (if ever).
Engine in bed? That's a new thought.
If this thing ever flys, I'll park it by Johnny Cash's cadillac.
Thanks,
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

I don't think you'd like the drive if the engine was up-front. It's a lot of weight and moving the cab back might make for an interesting hood/fender appearance, but I still think that a mid-ship mounting would be best. If you don't intend to do anything but show and brag, then what difference would it make? A one-ton chassis shouldn't be an issue. If you just want to get it to the roller status, then all you need is enough transmission to make it move.

Besides, you could get a Gear Vendors Over/Under drive unit and step it up. Put an SM-420 or SM-465 behind it....but the gearshifter is gonna be "odd". Automatic, even a GM dual-coupling hydramatic, would be the best ticket, in my opinion. But, it's your money....spend it!! You can't take it with you and you don't want the kids to fight over it, do you?

Re: GMC V-12 powered '91 Chev crewcab
 

I with you on mid-ship. I would like a drivable truck as end product. I never was a trailer queen fan, nothing wrong with show quality, but personally, I like to drive and use the stuff I put together and I live in lots of dirt and mud. Fuel consumption is the limiting factor on use. Tranny choice is optional. Just something beefy enough to stay in there under sensible use, AND the cheapest.
Thanks, All
Cayoterun

We're in the SKI group, too. Lovin' it, Price of fuel, won't take long. LOL

Re: GMC V-12 powered '91 Chev crewcab
 

Motor Length: I measured from tip of water pump shaft to rear of block. Almost even 5 (five) feet. Outside-outside manifold width is 24".
The 454 length is about 32" +-.

Front Axle weight: After comparing engine weights of a big V-8 to the V-12, it will add about 600# to front axle. I checked the data plate on my '97 Chev 1ton, and it lists 4100# GAW for front. I'm hoping the weight factor is doable since the truck won't ever be hauling more than a 1000# or so in the bed if we decide not to move the motor back.
Am I overlooking anything?
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

If you don't mind that the front end will sit lower & feel a little mushy, I don't see a problem. Guys run snow plows on little 1/2 tons all the time and get by. While most plow setups ain't quite that heavy, they are hanging WAY out front. You can bag the front springs too.

Re: GMC V-12 powered '91 Chev crewcab
 

Im gonna say mid engine big tunnel maybe a homemade body lift because you can make it better than any you can buy by raising the body mounts instead of plastic spacers, youll have to make some interesting linkage for the shifter but hay I think minimal modification is out the window at this point

Re: GMC V-12 powered '91 Chev crewcab
 

Happy and unexpected reunion!!!
First, I'd like to thank the couple pictured, Ted and Darla Summers, who made this reunion possible for this old engine and I after 43+ years.
The engine was put in service in 1964 on a new irrigation well pulling a 10" pump, pumping 2,000 gallons a minute.
I came home from overseas in Jan. 1965, went to work for the owner at that time. Cared for it for a year and changed jobs. The first owner (MMMallard, now deceased), used it 'til 1972, Sold it to this couple, and they ran it 'til sometime in the '80's. The motor broke a head, so he replaced it and put in the barn pictured. He learned I wanted to put a V-12 in a truck and told me what he had and if I wanted it. I jumped at the chance, then to add to my amazement, He said she's yours, FREE, bring her back to life.
Today is the first time she has seen daylight since the 198?
So this is the engine I intend to rebuild to running condition ( new internal parts are all no longer available) and put in the 1ton in all her former finery, which is pretty plain.
What a coincedence!
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

That is going to be an awesome project! I have a 351M V6 that I am dying to put in something myself. I have never seen one of the the V12's in person, but I can imagine how big it is. The V6's are huge and that is essentially two of them inline! FYI, if you didn't know all of the internals of the V12 like the pistons, rings, rods are the same as the 351. They have the same bore and stroke. 351 + 351 = 702

Re: GMC V-12 powered '91 Chev crewcab
 

considering the size and weight of the V12....have you ever considered rebuilding the engine and making a custom trailer for it? And it could power something, for show purposes....? Then pulling it behind your '91, or even something older?

Just a thought.

Re: GMC V-12 powered '91 Chev crewcab
 

There a several of those type demos through-out the plains states, and are really nice. They are alot more visible than this idea. I haven't seen one similar to what we're trying to do.
Would be fun to tow a trailer to the mountains and let those drivers of new trucks try to figure out how that old truck was hung on their rear bumper on long grades.
Based on everyone's imput and ideas, there's no telling where this project will lead us.
A standard cab flat-bed 1ton is already in the mix for consideration. Shorter wheel-base.
Thanks for all ideas and debate.
Cayoterun

Re: GMC V-12 powered '91 Chev crewcab
 

Hmmm... 4 exhaust maniflods....

QUAD TURBOS!!!

Re: GMC V-12 powered '91 Chev crewcab
 

Speaking of trailer-mounted....

Before I retired, we'd have a company come into our plant, periodically, and clean some big tanks for us. They had a flatbed-mounted V-16 engine that drove a pump. The engine was HUGE!! It would make four of your V-12's to equal the overall length of that beast.

I used to belong to a car club that had joint shows with the Rusty Wheels Engine Club, here in Arkansas. One of their members, also one of ours, had a 1960 Chevy Conventional cab tractor (single-axle) that pulled a low-boy trailer. Mounted on that trailer was a 1920 Fairbanks 2-cycle diesel that had been used to drive an irrigation pump near the rice fields of Stuttgart, AR. He nicknamed it Miss Smoke Rings. It took a 3-horse hit/miss Fairbanks engine driving an old air compressor that was used to start the diesel, after he had built a fire on the head of the cylinder. Once he had enough pressure and the head was hot enough, he'd grab the flywheel (it was about 6-feet in diameter) and start trying to start the engine. Once he had it running, he'd idle it down and add fuel to it, You could count the RPM's by the number of smoke rings that it would shoot out of the exhaust pipe...a pipe that was 12-inches in diameter. Best I remember, it would idle at something like 30RPM's.

Re: GMC V-12 powered '91 Chev crewcab
 

That's cool ! saw one years ago @ the Portland swap meet .Never forgot it
I think there is alot of good idea's however I can't shake the idea of that
engine under cab as in one of those early COE model's mid 50's or earlier
with your 91 frame modified to order ? GOOD LUCK whatever you choose
can't wait to see where it end's up !

Re: GMC V-12 powered '91 Chev crewcab
 

As far as transmissions go, a split gear SM420 from a 60-66 GMC 2 1/2 ton truck would work, but I have NO IDEA how you would shift it if mid mounted.

The SM420 has the same bolt pattern as the v-12 since it was mounted behind thousands of 305 and 351 v-6's.