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

[68GMCCustom]

and the tranny is?

[cayoterun]

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

[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

[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.

[cayoterun]

#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

[jeffspower]

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.

[ChevLoRay]

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.

[Scott68-93-97]

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

[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.