GMC V12

[rocketraider]

Showing my ignorance- I never knew these nasty engines existed until today. Used in 1960-65 GMC HD trucks.

They were apparently pretty thirsty, is why they disappeared from road use.

This one is running on propane and was used as an irrigation engine.

[R W Burgess]

The diesel engines of the time were much more fuel efficient.

My dad had a used V-6 GMC pickup (a similar engine, heads, etc.) at one time, sounded good.

[rhb1999]

I understand GMC also used a 3-cylinder diesel aka as the Detroit Diesel 3-71.

[Bleach]

There are a few more videos with the engine in a 62 GMC.

[rocketraider]

There were several early-60s V6 GMC pickups around home and I see one from time to time at cruise nights. Impressive, torquey engines.

In addition to the 62 GMC flatbed vids, there's a vid of one pulling to 5000 RPM, and it amazed me how quickly it spun up. It was modded a little but still a sweet engine blasting thru its pipes.

[rowan782]

Used in the Viking series I think. Friend put one of these engines in an Oliver farm tractor.

[rhb1999]

BUT, where the early GMC V-6 pickup trucks diesel or gas? I'm thinking at lest some were gas, someone correct me if I'm wrong.

[Bill Harmatuk]

I have an owners manual around here somewhere that I robbed out of a HUGE GMC 10 wheeler,that was being scrapped, (long time ago). It shows the configuration of the 2 V-6 s hooked together. Can't remember how the distributer worked but it had a diagram in the manual. Showed the firing order also.

Wish my scanner worked.

I knew this topic would come up sooner or later.

Bill H

[Bill Harmatuk]

Early V-6s were gas. The V-12 was gas.

Bill H

[rhb1999]

I have an owners manual around here somewhere that I robbed out of a HUGE GMC 10 wheeler,that was being scrapped, (long time ago). It shows the configuration of the 2 V-6 s hooked together. Can't remember how the distributer worked but it had a diagram in the manual. Showed the firing order also.

Wish my scanner worked.

I knew this topic would come up sooner or later.

Bill H

MMmm, I've seen 2 Detroit Diesel 8V engines hooked together, for use in large boats also.

[NTX5467]

THANKS for that uTube link! That vid's been there since Nov 2007? Guess nobody thought to look for "V12" and "GMC" in the same search? LOL

Thanks!

NTX5467

[CarlLaFong]

I have an owners manual around here somewhere that I robbed out of a HUGE GMC 10 wheeler,that was being scrapped, (long time ago). It shows the configuration of the 2 V-6 s hooked together. Can't remember how the distributer worked but it had a diagram in the manual. Showed the firing order also.

Wish my scanner worked.

I knew this topic would come up sooner or later.

Bill H

The V12 had an oddball distributor with two six cylinder caps as well as two carbs and two, separate intake manifolds

[Guest Bob Call]

If you look further into the GMC V12 you will see that only the block, crankshaft and oil pan are V12. All the other parts, heads, distributors, etc are from the V6.

[Rusty_OToole]

The V6 and V12 were designed at the same time to use interchangeable parts. If they were thirsty so were other truck engines of similar power. Fuel economy was one reason diesels took over the heavy truck market. It was lack of sales due to diesel competition that caused their demise.

[CarlLaFong]

If you look further into the GMC V12 you will see that only the block, crankshaft and oil pan are V12. All the other parts, heads, distributors, etc are from the V6.

The distributor was unique to the V12

Antiques pictures | Antiques images

[Dandy Dave]

There was one of these trucks in daily use at a quarry south of here. You could always tell when it was comming as it had a sound all its own. Back when Men were men, gas was cheep, and most big trucks did not have AC, or power steering. We had a 1969 GMC cattle truck on the farm that my dad bought new. It had a V-6. Dandy Dave!

[paulrhd29nz]

Any one notice that the u-tube V12 is running on propane?

The is a beautifully restored 3/4 ton 4X4 fire truck V6 that comes to our local car show.

Paul

[Barry Wolk]

I had half of one of those in this. Biggest pistons I've ever seen.

[Guest Bob Call]

rhb1999

Are you sure it wasn't a 16V71? Like the gas V12's the Detroit Diesel V's used multiple heads per bank on the V12, V16 and V24. The 8V and 16V used the 8V heads (4 cylinders per head) and the 12V and 24V used the 6-71 6 cylinder heads (6 cylinders per head).

[Dandy Dave]

Speaking of Detroit, the the 6V-71's that were used in Ingersoll Rand 1100, and 1400 Air compressors back in the 70's and 80's, were V engines, and had 3 cylinder heads. Dandy Dave!

Edited December 8, 2011 by Dandy Dave (see edit history)

[padgett]

"6V-71's ... were V engines, and had 3 cylinder heads"

Run that by me again please ? Did one run across the V ?

[Barry Wolk]

They were two V-6 blocks that used 4 3-cylinder heads.

[padgett]

Oy. I read that as three ea. cylinder heads and not two three-cyl heads. Knew something did not sound rite.

[rhb1999]

rhb1999

Are you sure it wasn't a 16V71? Like the gas V12's the Detroit Diesel V's used multiple heads per bank on the V12, V16 and V24. The 8V and 16V used the 8V heads (4 cylinders per head) and the 12V and 24V used the 6-71 6 cylinder heads (6 cylinders per head).

No, The whole thing had 4 valve covers, 2 8-V Detroit Diesels linked together back to back. In all the years, working at a yacht building company this was the only 16-V configuration I seen using Detroit Diesel's and they used alot of Detroits going back to the '50's. I don't recall seeing a 16-V Detroit.

[Guest Bob Call]

Sorry about that 12V head mistake. The 71 series was made in 1, 2, 3, 4 and 6 inline, and 8, 12, 16 and 24 vee. Yeah, I know a 1 cylinder isn't an inline or half vee. The 6 cylinder was also made in horizontal configueration (6L and 6N) for low profile like in busses.

16V and 24V were primarily stationary industrial engines to power pumps, compressors, generators, etc.

Edited December 8, 2011 by Bob Call (see edit history)

[Dandy Dave]

"6V-71's ... were V engines, and had 3 cylinder heads"

Run that by me again please ? Did one run across the V ?

3 cylinders per head X 2. Lookey here....

Another link of Detriots in all types of configurations. Swishy hangs around the ACMOC site. (Antique Caterpillar Machinery Owners Club). This link pretty much say's it all about anything Detroit.

Edited December 9, 2011 by Dandy Dave
Added A Link (see edit history)

[Guest Dick Whittington]

I worked for a fleet from the early '60's to the late '80's. In one of the corporate buyouts, we inherited a '66 or '67 GMC tilt cab highway tractor with a V-12 gas engine. One point one mpg was a good day for fuel mileage. It averaged under one mpg more often that over one mpg. One torquey creature though. Hauled poultry meal from the rendering plant to the feed mill in East Texas.

[junkyardjeff]

I never knew they existed until one day at a junkyard I noticed a 60 to 66 GMC semi with V12 badges so I opened the hood and was suprised with what I saw,this truck had the normal p/u cab with a short hood that opened like a 30s truck and 1/2 of the motor was under the floor. I should have tried to buy it as it would have been a neat project but knew nothing about air brakes so I never checked on it.

[Guest Paul Christ]

I first became familiar with the GMC V12 when I started work on my '62 GMC truck (V6).

One of the resources that provided valuable information was the 6066 GMC Guy .

The link below discusses GMC V12 myths;

** click here **

The next link provides general information about the GMC V12;

** click here **

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[Rusty_OToole]

The V12 had ONE cylinder block, topped by 4 heads. They did it this way so the heads would interchange with the V6, a matter of cutting costs and streamlining production.

A local moving company had 3 or 4 of them from new. They were only used for a short time then I suspect the owner died or retired, the trucks sat around for years and years and were finally scrapped with very low miles on them.

The engine was quite low, they were COE style and the top of the engine was flush with the top of the frame. At least that was my impression at the time.

[junkyardjeff]

Probably used too much fuel.

The V12 had ONE cylinder block, topped by 4 heads. They did it this way so the heads would interchange with the V6, a matter of cutting costs and streamlining production.

A local moving company had 3 or 4 of them from new. They were only used for a short time then I suspect the owner died or retired, the trucks sat around for years and years and were finally scrapped with very low miles on them.

The engine was quite low, they were COE style and the top of the engine was flush with the top of the frame. At least that was my impression at the time.