Bottom End Knock? HELP :)

[RandomGuy]

I never witnessed / seen this first hand... but can anyone post detailed info on how bottom end knock or problems can sound like

I really hope its my exhaust bumping... but the noise is coming from the intake manifold side im afraid (im not sure, but htats what it soudns like from inside the car....)

No noise at idle... no noise at normal driving... but if u punch it even slightly, The "knocking" sound comes.... It is really getting to me... Any ideas? I HOPEEEEEEEEE its not the bottom end.

by the way its a 100% stock mitsubishi starion turbo w/ new top end 1000 miles ago.

[curtis73]

Rod knock sounds like someone hitting the block with a hammer. Valve clatter sounds like a "snick snick" near the top of the engine. Piston slap sounds like halfway between the two.

An exhaust leak usually sounds like a "tick tick" or "spit spit".

[MagicRat]

Curtis is correct about the sounds, there. It's tough to diagnose sounds on the net, but your description is pretty good.
I don't think its any kind of valve train noise, because usually that noise occurs all the time, and is not throttle dependent.

Are you sure its not preignition (ping?) Have you tried premium gas, or an octane booster additive? Have you tried retarding the ignition just a bit?
(I recall your engine should have a knock sensor......maybe your's isn't working?)

If you are not so lucky, you could have a bad rod bearing, (that makes a deeper clunk) or a bad piston pin, (makes a sharper rapping sound) or piston slap.
Piston slap often is worst at cold idle, but dminishes as the engine warms up and the piston expands.

Without any other info, I think its possible you have a loose or bad main bearing (not rod bearing) on the crankshaft.

The following also produce noise, but usually are heard at idle, too:
-Sometimes a bad harmonic balancer (on the front of the crankshaft) sounds just like a rod knock.
-A loose or cracked flywheel (or flexplate in an auto trans car) can also produce knock sounds.