1989 Pontiac Firebird Engine noise high rpms

1989 PONTIAC FIREBIRD
100,000 MILES • 5.0L • V8 • RWD • MANUAL
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ARTSYMOND
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After 2500 rpm the engine has a knock. I don't dare push to see if lose of power has occurred. A mechanic told me it was "shot" but wanted to pay me 500.$ seems like it could be solvable but I want a honest opinion. It is a rapid knocking it has to be piston but could it be a cracked valve or stuck valve? I'd like to know what I can do to find out if it is really "shot" or if it is something I could fix I my garage with limited tools or diagnose. It is my fav car fun to drive and would kill me to sale it over a simple fix. Also he told us 6500$ to fix as a poor car enthusiast I can't get a new crate 305... Please point me in a good direction!
Feb 22, 2015 at 9:52 AM
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HMAC300
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rev to 2500 and pull one plug wire at a time to isolate cylinder. a bad piston will sound more like a hard tapping noise and a rod which it sounds like will have a deeper sound. if the rod bearing hasn't spun inside the rod you can put a crank kit in it. Otherwise it's pretty much shot
Feb 22, 2015 at 10:46 AM