702 GMC V-12 powered '62 GMC 1-ton

[cayoterun]

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

[airdale94]

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?

[cayoterun]

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

[msgross]

maybe even 3-5gpm!

[cayoterun]

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

[68GMCCustom]

dry weight for the 702 = 1485 lbs!

[ChevLoRay]

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?

[cayoterun]

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

[msgross]

Originally Posted by cayoterun

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

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

[special-K]

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.

[cayoterun]

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

[cayoterun]

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

[jerry moss]

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.

[CrashEd]

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

[cayoterun]

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

[68GMCCustom]

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.

[ChevLoRay]

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?

[cayoterun]

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

[cayoterun]

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

[jeffspower]

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.

[A.T. RockDriller]

Ok....
I sure didn't think I would be chipping in on this ....but.......
Here ya' go.
Me, having a GMC V-6 in the ol' '63, right out there in the driveway, affords me the opportunity to speculate in person on the dimensional challenges at hand.
First of all....I sure wish you had a mid-'60's GMC to relocate that power-plant into.
That being said, The double six configuration...(other than the weight) sure wouldn't interrupt the passenger compartment nearly as much as you might think.
I encourage you to measure twice on this one.
If you were to mount it so the front six sat a few inches forward of where the stock V-6 sits....shorten up the fan assembly....cut the firewall and floor-boards a bit.....you might be able to get by with picking up the dog-house engine cover off of a P-30 van or something like that.
Bucket seats, a little fabbing....convert the "industrial/Truck bell housing bolt pattern to the light truck set-up...
Maybe go with an over-drive automatic tranny.
The weight thing sounds bad, but it's no big thing to put 1500 pounds over your steer axle. Some of that weight will transfer back anyway.

I'm thinkin' it might not be that extreme of a conversion, if you look closely at the amount of real estate available behind the core-support.
Maybe.

We'll be watchin' you.

[watahyahknow]

Originally Posted by A.T. RockDriller

Ok....
I sure didn't think I would be chipping in on this ....but.......
Here ya' go.
Me, having a GMC V-6 in the ol' '63, right out there in the driveway, affords me the opportunity to speculate in person on the dimensional challenges at hand.
First of all....I sure wish you had a mid-'60's GMC to relocate that power-plant into.
That being said, The double six configuration...(other than the weight) sure wouldn't interrupt the passenger compartment nearly as much as you might think.
I encourage you to measure twice on this one.
If you were to mount it so the front six sat a few inches forward of where the stock V-6 sits....shorten up the fan assembly....cut the firewall and floor-boards a bit.....you might be able to get by with picking up the dog-house engine cover off of a P-30 van or something like that.
Bucket seats, a little fabbing....convert the "industrial/Truck bell housing bolt pattern to the light truck set-up...
Maybe go with an over-drive automatic tranny.
The weight thing sounds bad, but it's no big thing to put 1500 pounds over your steer axle. Some of that weight will transfer back anyway.

I'm thinkin' it might not be that extreme of a conversion, if you look closely at the amount of real estate available behind the core-support.
Maybe.

We'll be watchin' you.

for the doghouse you could use a bucket from a wheelbarrow cut and welded to fit , its steel and will weld to the floor nicely
as for coupling two sixes : http://twotogo.homestead.com/index.html

[72armyswbtruck]

Gonna be one crazy ride....

[bad6772]

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........

[ChevLoRay]

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.