need help rb20 major issue

[pepegurr]

i went outside earlier to go to the store and the car would not start(was running fine but rich yesterday) im getting a LOUD knock sound from somewhere on top of the motor. it sounds almost like a valve sticking only way louder. its getting fuel, spark, & air but no ignition, not even a backfire or missfire. the sound is coming from either the #5 or #6 cyl, intake side. if anyone has any ideas or can at least point me in the right direction that would be wonderful as im clueless and this is my first rb.

[mott6904]

check to see if your timing belt jumped and a compression test.

[pepegurr]

i think it jumped time cuz its spinning over really easy but what i dont understand is how it could do that when it was running fine yesterday when i parked it. makes no sense unless the tensioner went bad right as i shut it off.

[mott6904]

i dont know... but if i had to take a stab at it i would say that if the belt was loose then the sudden rapid movement on the crank applied by the starter made the belt either rip the teeth off or just jumped. either way if it jumped it bad news.

[virus77]

timing belt gone?

[pepegurr]

the timing belt is a little loose but it is there and still has all the teeth. im goin to try to figure this out but if its gonna cost more than 1000-1500 im just gonna go ahead and put in my ls2 and call it a day. then the only question is what to do with the rb.

[mott6904]

you need to check the timing marks. just because the belt doesnt have any missing teeth doesnt mean it didnt jump. If its loose and engine turns over really fast then its a good chance it jumped and bent the valves.

[pepegurr]

i checked the timing marks and they are dead on, now im really confused. how loud would a collapsed lifter be? i can take a video if it would help*edit* i just spun the motor over by hand slowly and didnt encounter any resistance but it still makes the noise. could it be a sticking valve?

[themadscientist]

You rotated the motor with your hand and you got a knocking sound? You have a serious problem. Pull the valve cover where the sound is coming from and you may scream.