The Stovebolt Site Forums The Shop Area Engine Shop Engine swap.....big V6 to V8????

Okay, this is in a 1968 GMC 6700 (IIRC the number). It's a "truck"....prob called a 2 ton. It's a dump truck, if ya want to know. It's a friends, so I'm just doing some research.

Any how, it use to have a V6 Diesel, but someone swapped in a V6 Gas (the big V6)...suppose to have been the direct replacemnt when the V6 diesels died. Any how, if that engine ever died, what can bolt right up to the tranny? Can a 350 bolt up? From the 70's????

The tranny is a 5 speed and the rear end is a two speed axle.

Corrected. It is a GMC 5500. GVWR is under 24,000lbs.

Engine is a front support and bell housing support type...

No V8's will swap that I know of. That brings up an interesting question . . . was the V6 a 6-53 or 6-71? And if so, does the 305 family of GMC 6's have the same bellhousing as the 6-71's? And if that is the case, the one V8 that would fit fine is a 8V-71! :confused:

I guess I'll have to do some digging around under the hood then...

I'd say that the big gas V6 shares the same engine bolt pattern with the 6V53 Detroit.

Ken
The only gasoline V8 that may fit there would be the 637( a Big V6 gasoline with a pair of cylinders extra). Also a 702 V12 would do! Guess Jolly has all these anwers.

Below is Jolly's website on GMC trucks.

He has pages about engine ID and where to find the serial numbers. He also has a page showing which trannies were used.

GMC Trucs

Link not work for me.....

A bit sideways to the topic, but it appears from Jolly's page that the same 4-speed tranny attached to Chevy small blocks (a 283 in my case) will bolt up to the 305. Is that true?

Okay, now the link worked. (Before, the link was asking me to download something.....)

Edit-
The engine isn't stock...but... the 5500 was listed as "factory" being the 401 V6. The truck was originally coverted by the WA state Dept of Trans... when the diesel died, so I guess. It was bought by a school district from the state and then he got it from the school 2 years ago.

I'll have to look for an engine id and see what kind of "Big 6" is in it...

Edit 2-
Looking at the site, I know one thing...the engine is not from 68...since the the carb is a single barrel!!!! That much I do remember seeing!!! Man, who knows what engine it is...

Jamie,

They can use the same tranny, as long as the bolt pattern between the tranny and the bellhousing is the same, but the bellhousing for a small block (for a complete answer: all L4 153/151, L6 194/230/250/292, all V6-90' 200/229/262, all V8 - small blocks, all years up the new LS series engines, all the W 348/409, and all the bigblocks)do share the very same bolt pattern. But the big V6 truck engines do not. For sure they do not use the same engine to bellhousing bolt pattern. I may be wrong, but I see the same engine to bellhousing bolt pattern shared by the 53 series Detroit diesel 2 stroke engines and the big gasoline truck engines, the 305/351/401/478 V6, 637 V8 and the 702 V12. Dunno if the series 53 and 71 have the same bolt pattern either.

Well, I was wrong....the carb is a two barrel, looking at the intake and mounting holes.

Engine said 351C 0XXXX (x= forgot number) Looking at Jolly's site, I think it might have had the GM diesel (the one they said was replaced w/ gas engines a lot). I'll have to look at the VIN and see.

If I read the engine right, it's a 351 V6 and I'm guessing it has about 180HP and 312ft/lbs (gross). Enough to move it...

It was probably equipt with the toroflow GMC V6 originally. They were not considered very good engines.

The 305/351/401/478 family of V6 engines are fairly interchangeable.

Why would you want a small block V8 in that big of a truck? You would not be able to do the work you already do with the 351C V6. The V6 engines are very strong and reliable engines that produce a lot of torque at relatively low RPM's where a truck needs it the most. In a truck that big the small block would not really improve the gas mileage like in a pickup either.

But yes they can bolt in if you change the motor mounts and bellhousing to the small block version.

Ken, The detroit diesels I believe used a different bolt pattern from the light and medium duty GMC V6. But they did make the bigger V6's with the same SAE bolt pattern found on the detroits.

Well, until now, I knew "NOTHING" about the V6 GMC engines. I was worried, that if it ever went out, what can bolt up to the tranny. I guess if they are "strong and reliable", then I won't worry about ever swapping the motor.... since if it got to that point, it'll probably be another 20 years down the road (LOL).

As I said, this truck is a buddy's (and I wanted to know more about it), but he lives in the city and I'm in the country. So I get to "borrow" it more....

Edit-
This dump truck has a 23,000 GVWR. It's small for a dump truck, but bigger the the 1.5 tons. Ya see, it's as long (front bumper to dump gate, closed), as my full sized regular pickup! Small box, but it can fit in places (well, most) that a pickup can and dump!

Those little V6's are good for 300K + miles with a little care. Rebuild cost on one is hovering around $2-2.5K to have a mechanic do the install.

I have been very happy with these motors in my trucks (several 65 & 66 GMC 3/4 & 1 ton pickups).

That's not bad for rebuilding an engine.....

That bridge will be crossed when one gets to it.... if that bridge comes.

could of had a toroflo diesel most of the 71 series detroit diesels had a sae-1 and sae-2 bellhousings and are part of the timming gear covers but my detroit manuals are buried some where in storage so i'm not sure of the 53 series

The 351 will last you a long time as long as you don't run it wide open all day long. It will outpull a sbc any day of the week. we had a fleet of them in a lumberyard where I worked. One two ton had the Roadranger tranny, 5 speed overdrive with 2 speed rear end. I was able to haul 10 tons of sheetrock at 80 mph (as high as the speedometer went) without any problem. I would guess I had that truck at 100 empty.

No, my buddy, as mentioned, lives in the city. He purchased this for $1200 mainly to haul grass from his yard (big yard) to the dump (or where/whom ever it goes to).... he uses a 25HP Kubota tractor 4x4 to mow and the loader on it to load.

The truck can be considered retired. Be lucky if it will get 500 miles on it a year.... I didn't know much about this motor, so I wanted to do some research and I told him what I found too.

I'm borrowing it for some farm projects in the next few weeks. I plan to make a few trips hauling manure to put in the field. Only bad thing is, that engine likes to drink gas.... ugg.... oh well. (And I have a 500gal bulk storage tank too)