1988 chevy 5.7runs fine but has werid knock in bottom

[88stepside]

hi i have just put in a new 350tbi in my 88 step side the motor came out of a 90 gmc 4x4 it ran great was sitting around for a few months , it ran fine but i put it in my truck and it runs good but has a knock and like a pinging sounds from the bottom i have took off the fly wheel to see if it was cracked but to find nothing it runs great no power loss do sent smoke runs great just this knocking sound from the bottom near the oil pan what else could it be, please help me out this is my third motor that s been nothing but problems thanks.

 

[Klumpper]

Does it sound like there's parts of a tin can rolling around in the bottom? If so, it may be a spun bearing. If it's just a light tick, it might be a lifter or rocker. If it's a heavy tick, there's a possibility that it's a cracked piston or head, stuck lifter or bent push-rod, but you said you're not getting lost power.

'do sent smoke' - come again???

 

[chevy_man]

The only way to tell 100% is to start disassembling the motor until you find out what's broken. Funny enough, mine started doing probably the same thing a couple days ago. Does the noise go away under load?

 

[Swims350]

had an 86 do the same thing it went away once you hit the gas but on idle it had a low end knock, not a tick pr peck but a knock. We pulled it and found some bearings worn down and causing some slack in the rod end, which I figure was making the knock.