Engine: Knock in lower end

[corum]

The car is a 62 Hawk. Automatic, all stock except for Mallory distributor. About two weeks ago a sudden engine knock appeared. With the stethoscope I can hear it in the oil pan. Other symptoms:
--no drop in oil pressure
--noise is worse at idle esp when you rev her a little; it goes away at speed and seems to run fine
--less of a fairly loud clunk clunk as engine warms; also less frequent
--the noise indicates that something is loose

My various shade tree mechanic thoughts:
--bad crankshaft bearing?
--bad oil pump?
--bad timing gear?
--broken flex plate?

When I have time in the next week or so I am going to drop the oil pan and take a peek. I have asked a local mechanic to take a look as well, since I have had no real experience with a problem like this (and may not know what I am looking at unless it is very obvious).

Have any of you had similar problems? Any thoughts on what may be the cause of this? As always thanks so much for your time!

[Flashback]

I would check the flex plate, FIRST.

[52-fan]

I would check the flex plate, FIRST.

Me too. If the engine runs well except for the noise, check the simple things first.

[studegary]

You should be able to identify if the noise is coming from the front or rear of engine. This would lead you to timing gear/fuel pump or flex plate (of course could be something else).
If it is the flex plate, you should mostly notice it on first applying a load.
Is the engine/transmission combination original? If not, it may not have been aligned (dialed-in). This will cause flex plate damage/breakage and should be fixed along with the flex plate (if that is the problem).

[karterfred88]

Sounds "flex-plate-ish" to me. Loose rods etc. don't quiet down with warmth and driving. Cracked flex plate will produce a bad knock, but as things warm up, warp as they are supposed to and sometimes get quiet--just before they finally break. Other knock that sounds bad, is when the fuel pump bolts back out and let the pump move on the front cover. Easy to check that, flex plate a little more involved.

[tempestan]

I agree that it sounds like a flex plate issue........and probably the easiest to check. tempestan

[hobiejack11]

I would go with the flex plate as my first long distance diagnosis for several reasons, You say it started all at once, rods or mains usually don't and surely don't get quieter when the oil gets hot. If it were bearings there would be an obvious drop in oil pressure. You can isolate a rod knock by pulling of the plug wires one at a time. Main bearing knock is detected most loudly when the engine is revved up to around 2K and then allowed to run over as it slowly decreases in speed (run over). A cracked flex plate will sound exactly as you described.