The motor is absolutely not worth it. Tearing down for the experience, or to try and identify the issue, would be entertaining. A good running 305 V6 can be had for $200-$500. They are a 100% boat anchor for "performance" and max out at about 3400 rpm. Good torque, well built. If I had this situation and I would buy another or drop in a SBC or BBC. The motor is just rare enough, and has a following, to where the parts are worth money. Pistons, rings, some of the valve train, gears, timing chain, and other parts are either expensive or a bit hard to find for a rebuild. The nostalgia factor of being his Dad's truck, bought new, may have an effect. This is why I'm trying so hard, and seem so silly, to find a way to get it going without teardown. I do realize everyone is probably right and a teardown is already past due. I will report back in a week or two. I am familiar with these motors and they are an engineering marvel. They have a very very strong oiling and water circulation design. Very strong metallurgy. Could withstand the lack of oil and washing.
Motor designed for 200,000 miles back in 1959 after GMC told to cease and desist in selling trucks with Pontiac V8's with a GMC sticker on valve covers.
First GMC V6: HIGH OUTPUT OIL PUMP: capable of pumping 14 gallons of oil per minute, provides extra circulation at all engine speeds . . . extra protection and well oiled surfaces on all vital moving parts. Engine is lubricated as soon as it's started. Cam lobes dip into a built-in reservoir of oil as the camshaft rotates, preventing cam and valve scuffing - a major reason why this engine gives long, dependable service.
135 GALLONS OF WATER: (at 3400 r.p.m.) Are pumped through this engine every minute. With thermostat open, only half the water goes to the radiator, the other half returns to the pump through a by-pass. This results in excellent cooling ability. There is less than four degrees variation in water temperature throughout the engine. This checks the possibility of hot spots. Here's cooling efficiency that is not matched by any other comparable size engine. Life of pistons, valves, valve guides and spark plugs in much greater, and the possibility of head-cracking is held safely in check . . . further proof of the durability and long life that is built into this engine.
FULLY-MATCHED COMBUSTION CHAMBERS Smooth, precision-machined combustion chamber minimizes carbon deposits, hot spots & pre-ignition. & there is uniform combustion in all 6 cylinders for smoothest engine operation. 6 equally-spaced head bolts surround each cylinder to reduce bore distortion, & guarantee gasket sealing for long engine service.
RELIABLE TIMING LINKAGE V-6 roller timing chains are double-strand, for double durability.
FREE-BREATHING INTAKE VALVES Forged from steels with high resistance to warping, pitting, & wear, extra-large intake valves let the V-6 breath freely, for higher volumetric efficiency.
FREE-VENTING EXHAUST VALVES Compared with other engines of equal displacement, V-6's have the largest exhaust valves of all -- to keep back pressure low, efficiency high.
HARD FACES & INSERTS Tough, Silchrome XB-steel exhaust valves, hard-faced with Ni-Chrome
Spark plugs are on the inside at top of motor away from exhaust manifolds. Long reach plugs provide greater heat sinking. Plug wires stay on top of motor.
"SCUFFPROOFING"DIP Before pressure lubrication takes over on engine starts, V-6 cam lobes dip into a special oil reservoir. No "dry scuffing" mare cam or valve-lifter faces!
POSITIVE VALVE ROTATION A positive ratchet action rotates every valve on each cycle. Contact surfaces stay clean for positive seating. Standard, 305C & up
M400 CONNECTING ROD BEARINGS Big, long-life M400 bearings are used in V-6 connecting rods. Low-friction tin & aluminum alloys are backed with a layer of steel for extra strength.
EXTRA-LARGE MAIN BEARINGS Huge, M400 main bearings provide solid support for the crankshaft, & resist wear by spreading the load over extra square inches of bearing area.
PRECISION-FITTED PISTONS In every V-6 the big, deep-skirt aluminum pistons are weight-matched, & precision-fitted to the bores, a cast-in steel band controls heat expansion.
SHORT, RIGID CAMSHAFT Extra-wide camshaft lobes are flame hardened & phosphate coated to resist wear. Four big bearings carry the shaft for precise valve operation.
RUGGED CONNECTING RODS Piston power flows smoothly to the crankshaft through big, forged-steel, I-beam connecting rods -- all balanced to within the weight of a cigarette!
SHORT, STIFF CRANKSHAFT This husky crankshaft helps conserve engine power & extends bearing life, because it has the strength & balance to minimize deflection & vibration.
RIGID, RUGGED BLOCK This block has strength to spare for resisting internal strain -- strength from it's super-tough iron alloy, staggered cylinders & short, deep-skirt design.
M400 is Monel. 80,000-90,000 PSI tensile. High corrosion resistance.
How's this for a demonstration? Spinning motor from the rear.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
