I have a 97 z28 with 108k on it... My transmission went out about a month ago and its been sitting at my shop untouched since. Well today i was gonna pull it down to the tranny shop to have the tranny rebuilt so i fired it to have it pulled and when i did so it started knocking horribly... i shut it off because i had no idea what it was. I started it back up a few minutes later and let it run.. there was a bad knock then after oil pressure came up it quited down a little but is still loud its more then just a slight tick. I have no idea what would cause it since it ran fine when i parked it. Any ideas?

 

Depends on what kind of "knock" it is. Could be a bad lifter. Could be a rod knock...
What does it sound like? It is high pitched almost a metallic "tingy" like or is it low and deep?

 

i dont know how it would be a rod knock since it was fine right before i parked it.... it honestly sounds like someone is hitting the valve cover with a hammer i know what piston slap sounds like and i know what a bent rod sounds like this is a bad slapping almost noise

 

Have you taken the valve covers off yet?

 

lifters bled down?, I would let it run for a little while after you get it back together and see if it clears up if it is a tick like sound, if it is a deep sound it may be more than a lifter.

 

well it sounded like it was for sure coming from the passenger side so i tore the valve cover off last night and at first glance everything seems to be alright... im gonna take my rockers off tonight and see if i broke a rod or something.... my brother thinks one of my valves is stuck shut after sitting for so long and after i started it i broke a valve spring or something

 

Maybe someone started your car and reved the hell out of it?
ayways best of luck, i hope it is something minor.

 

if it sat for a month your lifters could of bled down. like the other person said, run it for a minute or two and see if the lifters pump back up once they get some good oil back in there. i would also see if any of your rockers are loose

 

i let it run for a minute but it still knocked louder then **** so i just shut it off... i tried to do a compression check last night but i cant even get to the damn spark plugs this car is retarted to work on haha

 

Is the car in an Auto shop? Doesnt anyone there know anything about cars?

 

it was probably because the oil bleed down from sitting for a while, just like when you change your oil it ticks loud until it builds oil pressure.