The Stovebolt Site Forums The Shop Area Engine Shop 1955 2nd Series GMC V8 identification

A friend has a 55 2nd Series GMC with a good sized V8 in it, original to the truck, that had the V8 badging as well. How can i identify the size of the motor? I think it is the larger size which i think is a 318 V8 cu in Pontiac motor. It has the 4 barrel intake and carter carb. Has been sitting for a long time and i assume it is stuck. Any rarity to this engine if it is original? Thanks for the help.

318 is a MOPAR engine. '55 Pontiac is a 287. '56 Pontiac is 316.

'55 Chevy would be 324 or 265. The 324 was an Oldsmobile engine.

Assuming it is an original "GMC" V8 it is basically a Pontiac V8 from 1955 with dished pistons lowering the compression ratio from the Pontiacs 8.0:1 to 7.6 if I remember right. Look for the engine serial number on the passenger's side as shown below. The first 3 digits are the engine size. In 1955, Pontiac called the engine a 287 while GMC called it a 288. There are rumors in the GMC Master Parts Book that some of the 55.2 trucks came equipped with 316 cubic inch (1956 Pontiac 317) engines, but I've never seen one.

In any case, none of the Pontiac-based GMC V8 engines came from the factory with a 4 barrel carb. They were all Bendix-Stromberg WW-203 two barrel carbs.

Check the data plate on the driver's side door jam. A 55.2 model would have a serial number like 1028YP12345
where 10 is the model number, 10 is 1/2 ton, 15 is 3/4, 25 is 1 ton
where 1 is the wheelbase length, in 1/2 ton 1 = 114", 2 = 123"
8 is 8 cylinder. If a 6 cylinder there is no 6, just blank space
Y is the year. Y = 55.2, X = 56, T = 57, S = 58/59
P is the plant that the truck was built in, P = Pontiac Michigan, C = Oakland California
12345 these trailing digits are the actual chassis serial number.

Chevrolet never used an Oldsmobile engine, the only V8 available in the 1955 Chevrolet was the 265. GMC did used Oldsmobile and Pontiac engines through the years.

Mike B

Pontiac Block Casting.
1955 287 (288) 518037
1956 316 521560
The block casting number is located on the right side (passenger's side) of the engine block below the cylinder head surface and is centered between the freeze plug holes.

Pontiac V8 4 Barrel intake casting number.
55 278 (GMC 288 55-56) #521512
56 316 (GMC 316 55-56) #521570
They are located on the number 1 intake runner by the thermostat

The two intake are interchangeable. But like Bill said “none of the Pontiac-based GMC V8 engines came from the factory with a 4-barrel carb, so it could have been added later.
Rarity ?

Chevy used to run Buick V-8 engines in some of the larger trucks.

George

George is correct, Chevrolet used the 322 Buick Nail Head engine in the 1956/57 9000 and 10000 Series trucks. This was the only engine available in these trucks in both 2 and 4 barrel configurations. In 1958 the 348 became the new engine for the big trucks with the 322 still being used on the School Bus Chassis only, it seems school systems didn't want to be the guinea pig for new engines, so the tried and true 322 stayed on for a couple more years just for them.

The Chevrolet version of the Buick 322 was made with a few upgrades to make it stand up to the challenges of heavy truck use. The water pump was made with a longer shaft housing to accommodate the roller bearing and the timing chain was a double roller (cars used a single roller). It's also rumored the block had a higher Nichol content, but I've never been able to confirm that.

Mike B

370 Olds engines were used in trucks, too!

Ed

Just to be clear, they were only in the GMC's.

Mike B

I was by the truck and took a picture of the engine mount for the V8, but forgot to get numbers off of it, hope to do that next time i am by it. I've never seen a V8 with the engine mount in the very front like this one. Again, looks like original equipment to me.
And the truck did have the v8 emblems on the fenders.

It is the original type mount. I broke one on my '57. I had a fan shroud (added with A/C) that made a helluva racket when the fan hit it going around left turns with a little throttle. At least I knew something was wrong.

Ouch, that doesn't sound good at all !

I was able to ID the engine as a 1959 Pontiac V8 389. The block had 532000 stamped on the PS which coincides to a 1959 engine. So it's obviously not original to the truck. But i'm guessing the truck came with a V8 originally since it had V8 Badging on the fenders. I was surprised to find that the 389 engine was not stuck!

Definitely a Pontiac engine- - - -those horizontal rubber hoses in front of the block were common to all the Pontiac engines in the 1950s and early 60s. The Carter AFB carb is from somewhere in the middle to late 1960s, I believe, so it's definitely not original equipment. Looks like you've got somewhat of a mixmaster there, or at least an "upgrade" to some newer parts sometime during its earlier life!
Jerry

'59 was the last year of the "horizontal rubber hoses". They were part of the "reverse flow" cooling where the cooler flow from the water pump went to the heads first and then down into the block. In 1960 Pontiac changed over to the more conventional flow into the block first, then into the heads.

Carter AFB carbs were available on Pontiac V8 engines as early as 1957, so yours may be original (or original type) to the engine.

This page (from a Pontiac Master Parts Catalog) MAY help you identify a '59 engine. I say MAY, because the early '59 engines were identified by a decal on the passenger's side valve cover (probably long gone on yours), but late '59 engines had a letter code stamped on the front of the block passenger side just below where the head joined the block.