My 81 WONT RUN

Ok I have a 1981 GMC Sierra with an in line 6. I have replaced the alternater, battery, spark plugs, spark plaug wires, distributer cap, rotor button, starter sylenoid, and ignition coil. The problem is this: When I turn the key, the engine will turn over but it won't run. Any suggestion????? Please reply.

I'll assume you checked for spark and there is non.
first check to make sure the distributor rotor is turning while the engine is cranking if not the distributor is damaged or the timing gear on the crank is destroyed. if the rotor turns check for 12v at the positive coil terminal, if it's not there check the fuses and ignition wiring/switch. if you have 12V and no spark it's probably the ignition module.

if it has spark make sure it's getting fuel.
no fuel could be a clogged fuel filter, bad pump or empty tank(I hope not!)
If you have spark and fuel the thing should run if it sputters but won't catch try turning the distributor untill it starts.
okay theres one more possibility. low compression this might occur if it's been flooded, the gas will wash oil off the cylinder walls. you can add a little bit(teaspoon should do it) of oil to each sparkplug hole to bring it back. good luck!! hopefully this helps you in your diagnosis.

oh it's actually the timing gear on the cam that bites the dust not the crank usually.