will not crank at all

[srGS-t]

ok I have fuel i have spark......but yet it will not crank. it just trys to turn over......every now and then it will back fire threw the tail pipe or even threw the t-body. im lost i mean i cant think of anything......i changed the starter and i look at the timeing marks and the look to be right on sooo what else could cause this....please help anybody

 

[madtech707]

By saying "will not crank." you mean that the crankshaft does not turn at all. Right? If so then try turning the crankshaft manually with a ratchet and socket on the crank pully bolt. If you can turn it by hand then your problem is in your starting system. If you can't turn it by hand then most likely your starter wont be able to ether. Meaning that you serious mechanical interferance in the engine ifself.