gerifexgroup

I have a 2000 Grand Cherokee laredo with a 4.7L V8 (WJ). the radiator has an opening under it and could not supply water to the Engine, so that cause the Engine to over heat. Had a mechanic check and found out that two valve was bad(bent) and also giving a knocking sound when the Engine is on which he believe that the metal is bad. he replaced the two valve and metal (without changing main bearing because he believe the main bearing is good). but after the replcement, the engine sounds fine when cold but it drop to zero point when hot. The engine sounds good when it is first started (Cold). When the engine is hot, it started jecking and shooting and then off. please can any one help in solving this problem for me.

Thanks for any advice