So I pulled my motor and installed cam and GT40 heads. While I had the trans out i installed a new clutch. Reinstalled motor and it ran great let idle for approximately 20 mins then I heard a noise like something may contact in the motor then it was back quiet and running great. I switched off and pulled valve covers just to take a look and everything looked good. I put a bar on the crank and it turns over about 1.5 turns in either direction then stops like it hits something?? I first thought valve to piston clearance but since it was running great for the first 20 mins could that be possible. Could it be that a bolt backed out of the flywheel or timing component?? I did use loctite.I also installed comp cam valve springs. Any help would be appreciated I really hate to have to tear it back down.