The Stovebolt Site Forums The Shop Area Engine Shop 1959 GMC 336 engine identification questions

I recently purchased my dad's 1959 GMC fleetside VIN# 101 8P PS16062A. This truck has been owned continuously by my dad, then my brother and now me. The truck is in spectacular shape and all of the drive train components are original.

It has (I think) the 336 V8 with a 4 spd manual trans.
The engine has approximately 100k miles and I am thinking of having it rebuilt. I am confused however as to what exact enginge it has.

Based on research to date I think it is a GMC 336 derived from a 1958 Pontiac 370. I would like to be certain of this and would appreciate any help. The only casting code on engine is 530046. There is no GMC number such as 336-35001. The casting number on the intake manifold is 5285 and the number on the exhaust manifold is 528596.

Do I have a 336 based on the 1958 Pontiac 370, or could they have simply put a fully bored 370 in it???

Any info on this would be greatly appreciated.

Thanks,

Ray

Hy Sasto's 59 Gmc, welcome, the serial number for the engine should be on the right (passenger) side of the block just above the oil pan in roughly the center of the block. There are two totally different 336s one for 1958 and one for 1959, so the serial number is very important. You could also try Old GMC Trucks as well for more info, hope that helps.

There were two V8's available, 347 and 336. Don't know that they are "based" on anything. . Your "VIN" is 1/2T short, V8 built in Pontiac MI, second "P" unknown, S= 58-59. Info indicates 336 used in BigBig trucks. 101-8's were 347 with trans SM320.
V8 Engine serial number located right side below manifold to front of drain cock.

Bartamos,

Your response is contradicted by the following. I still don't have a good answer to my question.

The GMC/Pontiac V-8. (by Bill Hanlon) From 1955 through 1959 small (less than 2 ton) GMC trucks with gasoline V8s were equipped with Pontiac V8s. In 55, 56 and 57 they were almost identical (bigger dishes in pistons for even lower compression ratios and Bendix/Stromberg carbs) to same year Pontiacs. In 58 they used the same block as Pontiac, but only bored it to 3.875" giving a 336.1 cubic inch engine instead of Pontiac's 370. In 59 they again used the same block as Pontiac, but only bored it to 3.78" giving 336.9 cubic inches instead of Pontiac's 389. Cranks, heads, rods, were the same as same year Pontiacs -- except the smaller bore GMC engines in 58/59 required different balancing, hence different cranks.

Wikipedia
336
GMC's own V8 was the 336-cubic-inch (5.5 L) OHV/pushrod engine. It used a 3.875 in (98.4 mm) bore and was produced only in 1958 and 1959.
While both the '58 and '59 GMC V8 engines were advertised as 336-cubic-inch (5.5 L), the '58 version was based on the Pontiac 370-cubic-inch (6.1 L), but with a smaller 3.875-inch bore giving 336.1 cubic inches (5,508 cc). The '59 version was based on Pontiac's 389-cubic-inch (6.4 L), but with a smaller 3.78-inch bore giving 336.9 cubic inches (5,521 cc).

Anyone else have any info?

Mystery solved. I never found a GMC number on the block, but I did locate a copy of my dad's original title which had a GMC engine number on it-- 336 05181. Thus, it must be the 336 based on the '58 Pontiac 370 but with the 3.875 bore.

Thanks everyone for your help.

Hello, I recently purchased a very similar truck - 1959 GMC 100 LWB with what is believed to be the original Pontiac 336.
The truck has the same cast code as Sasto's - 530046, and as was the case with him, there was no Serial number or stamped code on the front of the block....

Other codes were as follows:
Block date code - L 10 7
Intake - 528577
Timing Cover - 518034
Head - 528511
Both driver and passenger heads date from Dec. 57 as well.

All seem to point to this being the original engine, but was wondering what, if anything more, could be used to make sure....
Also, the column shifter is absolutely shot and am in the market for a floor shifter for the existing 3 speed:
The three speed is stamped GM-19, case casting 8743368, date casting F 10 7....any experience with a Hurst universal floor shifter and this transmission would be appreciated! Thank you.

Displacement explained:
Early (370 based) 336.1: 3.875" X 3.5625" (short stroke)
Late (389 based) 336.7: 3.78" X 3.75" (long stroke)

Thanks for the reply. Would there be any way to determine early or late without the serial number or tearing into the block?

Good find panic!