Kocking.. Won't Start

My girlfriends 97' Lumina with 160000 miles knocks really hard and won't start after sitting for a couple of hours. It takes a few tries to get it started... Suggestions?

Hmm, losing coolant but can't find where? Most likely the engine is toast..

It was leaking anti-freeze a few months ago..We had some kind of gaskets replaced and everything seemed fine. I did notice something on the drive way but I figure it was from air conditioner. What do you think.. Anti-Freeze level did kind look low? Anything we can do right now?

Sounds like it spun a bearing or something equally awful.

It has always knocked it's just getting worse... I am not a real big car enthuasits.. So what are you talking about? How much to fix?

I'll assume the "knock" is piston slap, which sooner or later is going to blow the engine. I'll also assume that the engine still starts, just not right away. Correct me if my assumptions are wrong. First thing to check is for cloudy/milky oil. This would indicate coolant in the oil and that's bad, indicating a head gaket or another intake issue. How long has it been since a tune-up has been done? Most hard start situations involve worn plugs, bad wires, etc..., so don't look for big problems until regular maintenance has been done.

I assume you had the intake gaskets changed? It may have not been caught quick enough and did damage to the rod/main bearings, and possibly the cam bearings. Piston slap is also a real scenario. Either way, your looking at most likely an engine replacement..

Would it always do it... if if was a slap.. Girlfriend says it only happens sometimes.. Not all the time..

The coolant isn't leaking and the oil looks fine. The car didn't knock when I tried it. It only happen maybe 2 of 5 times but when it does happen it won't start. Possibly be just needed a full service.. Plugs wires.. the works?

Actually, piston slap is a common occurance with 3X00 engines. GM admits it, but states it's normal. Piston slap will dis-appear once the engine is warm, because the piston will swell up and fit the cylinder better.

It doesn't slap after being started.. It only knocks while being started.. I listen to it yesterday... Its not really loud but it does sometime cause the car not to start...

Hmm, that's odd. Starter gear, flywheel maybe? It's hard to say without listening to it.

Car hasn't done it now for a few days.. Starts fine.. possibly bad gas?

I have no idea.. I'm stumped.