Won't start I just redid the head gasket?

I just redid the head gasket on it and I assembled the timing marks and everything for the timing on the valves line up with the marks on the chain and on the camshaft but for some reason it won't start when I crank it over and I moved to distributor it will make like a loud crunching kind of grinding noise on one side but if I move it back together it won't make that noise and it will crank over like normal but it won't start I've had it start up a couple times but barely was running I had to pedal to the floor and still it didn't keep it running that long before it shut off I don't know why it's not wanting to start I think I lined everything up right it's a fourth time I've had to tear the engine down all the way to the timing chain can anybody please give me some insight on what it probably is and what I need to do