I have a GMC 336 that I'm using in a 1958 GMC 3/4 ton NAPCO I'm restoring. The engine is in the shop now. Anyway, the guys at the shop called me and wanted to know if I had an early, mid, or late GMC 336? The block serial number is 33603131. I believe this is an early block based on the Pontiac 370. It also has completely dished pistons. Not the partially dished pistons. Block casting number is 530046. Just wanted some verification from someone "in the know" to make sure I'm correct before I tell the shop to order engine rebuild kit. Appreciate the help.
The only reason to run dish-top piston is so a truck can haul a max weight cargo load at wide open throttle, lugging the engine down while burning the cheapest grade of regular gasoline available without running into detonation problems. Unless you're building a truck that actually works for a living, not a Cowboy Cadillac, run a set of flat tops that fit the bore and stroke and get the benefit of a little more power. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
You're right. That is the early one. The later one was based on the Pontiac 389. I can't remember if it had dished pistons, but I don't think so. I also think the bore and stroke on the 2 may have been different. But I could be wrong on that. Haven't had one of those apart since around 1972. All the later ones had a problem with oil leaks where the oil filter mount attached to the block. I remember that very well. Wasn't easy to fix, either.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Never worked a truck Pontiac engine, but Pontiac passenger engines like flat top pistons.
Jon.
Good carburetion is fuelish hot air The most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes! The Carburetor Shop
The early 336 V8 (engine serial number less than 336035000) used '58 Pontiac 370 crankshaft dimensions while the late 336 V8 (engine serial 336 035001 and up) used '59 Pontiac 389 dimensions. Never heard of a "mid 336".
Picture shows the location of the engine serial number on the passenger's side of the engine.
Last edited by Bill Hanlon; 01/29/202212:11 AM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
