need help. loud hitting noise when starting

[justin4260]

i went out to start my truck this morning. i just put a new battery in it and i was going to adjust the air fuel mixture. when i turn the key the engine turns over but then i hear a really loud hitting noise by the started it sounds like. the noise is so awful i stopped turning the key as soon as i heard it. i would take a video of the noise but id rather not make it again. i tried to start it one more time and it did the same thing. i checked the fly wheel and there are wear marks on a lot of the gears. some grinder down spots and some just were it rubbed of the black dried grease.