Demoralized

[64dartgt]

Well I put my new mechanics stethoscope to use today to put the end to my denial.  The thump in my completely rebuilt engine (a few years ago but barely driven...less then 200 miles) is clearly from the middle of the oil pan.  What is odd is that it is irregular at times.  At idle it is about once a second but then it occasionally skips a beat and the next beat is double.  If I pull the pan will I be able to see a spun bearing?  Is there any chance it is the oil pickup tapping on something?  The windage tray?  But it is quiet in the back of the pan.  It is just weird that it isn't regular.

I also picked up a $30 wired remote mic made to use to diagnose my 60+ mph rear end noise.

Spending so much money on a car just to have major problems associated with work from reputable rebuilders (engine and rear end) really bites.

I would probably give up if I could get half of what I put into the car already.  It is a nicely optioned 73 Charger (factory sunroof, console, power windows and AC) but it is still just a small block 3rd gen.  It is not like I will ever get even $25K out of it if I put that into it and I am halfway there with not body work or paint yet!

Bob

[Challenger340]

At idle it is about once a second but then it occasionally skips a beat and the next beat is double.
If the engine will run steady, you may wish to remove 1 spark plug at a time right at the distributor, to see if you can "short out", or change the sound of  the knock ?
Wear gloves and use well insulated pliers as invariably the high voltage spark will want to jump to ground, or you for a shock.
Usually a sharp double "wrap" sound is a Wrist Pin, and tinnier than a rod bearing.

You may also wish to tap in a Mechanical Oil Pressure Gauge, to read "actual" Oil pressure while running ? Bearings will invariable drop Oil Pressure substantially, Piston wrist pins won't.

Spending so much money on a car just to have major problems associated with work from reputable rebuilders (engine and rear end) really bites.
That bites !
Is it a performance engine ?   
I can't get into why they don't stand good for their stuff.... suffice to say, we Dyno everything we do here in the Customer's presence, to their satisfaction, BEFORE it leaves.  Just the only way to conduct good business in our market, if there is a problem we would like to know FIRST !
It costs more, but 100% satisfied Customers.

[BSB67]

When did it start?  Has it always been there?

For all of the "I think I have a bad bearing" suspicions that I've been around (on non-raced, fresh motors) they have never been a bearing.

Please describe all of the things that you have done to prove with 100% certainty that it is not a lifter, rocker, exhaust leak, converter bolt......

Tearing into the motor is not the first or second thing you should do.

[64dartgt]

It has always been there.  It is a stock rebuild of a high compression 1971 block with a Comp XE 262 cam, but the engine is 0.060 over and one bore is sleeved.  The rebuilder is a professional and a Mopar guy.  He listened to the sound and did not think it a bearing.  It sounds just like someone thumping on a 5 gallon buckets bottom.  It starts when the oil is warm..

I put a mechanical oil pressure gauge on it and pressure is fine.  I used a mechanics stethoscope and the noise is loudest from the middle of the oil pan.   The noise is not apparent at the fuel pump, the valve covers, etc...

I will happily send a sound file to anyone who would like to help.  The only thing I can think of is to see if I can pull the pan and see what is going on.  Could it be the  oil pickup tube tapping on the windage tray?  The oil pan?  I should see shiny spots if something is rubbing.  A wiped main or rod bearing should be obvious too right?  Can I do it without pulling the engine or is that just easiest. 

Is a shame.  The car runs mint.

[68Charger4me]

I've had a converter bolt hitting the shield and it sounded just like that, just food for thought.

[ws23rt]

You say it sounds like something thumping on a 5 gallon bucket bottom?--

That kind of sound can only come from something like a bucket. --The pan and or the windage tray?

Evidence ----The oil pickup is very close to the bottom of the pan.---The crank is very close to the windage tray. --- Your stethoscope test identifies the middle of the pan.--The oil pickup is near the middle of the pan.---The noise does not correspond consistently with the engine rpm.

My vote is that the oil pickup is not screwed in tight and is tapping the bottom of the pan. The next best thing I can think of is something was left in the pan or above the windage tray. (not as likely).  If in the pan something foreign can migrate under the pickup and engine vibration could smack it from time to time.