Technical Odd BBC Noise, take a guess!

Hey all! My 366 BBC-powered Bus developed an odd noise that has me concerned, since my wife and I live in the bus, and are 1000 miles from home.
-Rebuilt 366 by a speed shop, the works! New valvetrain, pistons, rods.. The works.. Has about 2000 miles on it so far, tons of power, oil pressure etc..
-Noise is metallic, like a wrench tapping on metal HOWEVER...
-Noise is irregular, (Slow), no tempo, not constant, not very loud
-Noise is coming from harmonic balancer area (Cannot find exact even with stethoscope)
-Noise is only at idle, when engine is hot
-Noise goes AWAY with RPM, even a slight increase quiets it down
-Drove 200miles to next campground with the noise, it's not any louder or worse. The engine is fine otherwise.....
-I read it may be the mechanical fuel pump, and heard pinching the fuel line would alleviate the issue if the rod or pump was the problem.. But no change...

Million dollar question... What is it??? I'm not in a good place to tear into the engine but do have the tools and skills to do so if it means not windowing the block...
Edit: Auto Trans and sound is not coming from there, just checked. In Fayetteville, NC currently. Headed to TN Next.

Edit: Removed fuel pump, rod is fine. Lever arm is loose and makes noise when jiggled back and forth, hopefully, this is the issue!? When I got the engine rebuilt I re-used the pump.. Heading to NAPA tomorrow for a new pump.

 

Thoughts thoughts, balancer coming apart, fuel pump making noise, I've had that happen ,timing chain slapping around at idle but once our rpm increases it kind of gets rid of the slop? Good luck

 

Torque convertor bolts or cracked flex plate?

 

Torque converter bolts or cracked flexplate

 

Automatic or Manual trans?
Have you pulled the belts off the front and run the engine?

 

May want to mention the area you’re currently in, where your next top is, etc. someone my be near by, or know where you can take it for another set of eyes/ears.
I feel for you, being far away from home and having an issue.

 

Just checked, all quiet from the bell housing area

 

Auto trans, noise is not from bell housing area. Have not pulled belts yet but, did give a listen to all accessories, all sound good.

 

Small exhaust gasket leak.

 

From my experience that would make a constant ticking sound

 

Flexplate bolts not tight.

 

Removing the belts can also help pinpoint noises coming from cracked, loose or bent pulleys, or loose, cracked or misaligned accesory mounting brackets. Check the fan blades while you're at it.

 

Depends how good the combustion is on that cylinder at idle.. still worth checking.

 

This ^^^^^ is a great diagnostic. It will eliminate water pump, steering pump, alt, ac.
I bought a 69 Gran Prix that the owner thought was a rod knock, turned out to be the balancer/dampener. His loss, my win.

 

Alternator mount bolts loose can cause strange noises.

 

Thinking fuel pump arm/spring. Pinching fuel line will not affect that noise.

 

Really? What would be a good diagnostic for the fuel pump? Remove it and see if the rod is mashed up or the arm jiggles?

 

thats a good possibility, some rebuilds use a bronze tip pushrod and the cam eats them up, it takes a fair amount of driving before you see it, if it continues it'll mushroom the engine side of the drive rod and you'll play hell trying to get it out.

 

Speaking of the FP, and danged if I can remember, but does the BBC have the hole you put a long bolt in to hold the rod in place when installing it? If so, maybe someone used too long of a bolt and it’s still nicking on he rod. Wick check if it has the hole/bolt in it.

 

I haven't had a big block in years, but it seems to me you could pull the fuel pump and run it on the fuel in the carb long enough to check. I don't think it's pressurized, but you can pull the pushrod and reinstall the pump if your worried about oil loss

 

cracked flexplate. drop the inspection cover and look closely around the crank flange portion of the flexplate. i had one last year that cracked in a full circle except for about a quarter inch. same symptoms you are describing. its not an expensive fix, and would not take that long to replace - just aggravating.

 

Yep the 366 has a 3/8" bolt hole in the front of the block to hold the FP push rod up while changing the pump, and a pipe plug below the FP mounting hole to remove the rod if necessary.

 

Similar to flex plate, a cracked water pump pulley or lower pulley.

 

Not pressured so much that a temp block off could not be fashioned from whatever material you can find,

 

I had the same problem on an O/T car with only 8 miles on it, I bought it off the showroom floor. Took it back into the dealership and they said the harmonic balancer came apart in pieces. Once they replaced that I never had the problem again.

Larry

 

Pull the pump and fire the engine. Sometimes they break the spring and it gets noisey. If the noise goes away you need to replace the pump.

 

I vote fuel pump. As said run it and verify it's making the noise. Remove the pump and start it and see if the noise is gone. Simple test.

 

Bad power steering pump

 

I like to use a short length of garden hose or heater hose to help locate noises...hold one end near your ear, other near the suspected source of noise. Be careful!

A few years ago I had a not very old fuel pump fail slowly in a strange way...the pivot pin for the arm worked out of where it was crimped into the housing.