From the factory, GMC 302 engines had either a 4.000" or (if needed because of machining problems) a 4.005" bore. Check the Engine Serial Number Suffix chart to see which your engine left the factory with. Even though the factory Maintenance Manual says the letter is placed AFTER the serial number (a suffix), I've only seen the letter as a prefix, never a suffix.
At the factory the actual bore of each cylinder was measured and then had a properly fitted piston installed. See the "Cylinder Bore Selected Sizes" chart.
Last edited by Bill Hanlon; 05/16/20253:24 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.
