Knock/rattle at lowish rpm. 455 *teardown/rebuild pg5*

I am. and I have a timing tape on the balancer

I just ran it up in the driveway:
850 (idle): 10
1000: 16
1200: 18
1400: 18
1600: 20
1800: 22
2000: 22
2200: 24
2400: 26

Its an oem distributor, 1112110, date code looks to be 1J27

 

Good Info, thanks! I can try taking the initial down to 6* and see what that does, but I remember the idle not being as nice from when I initially set it up.

 

I had the vac advance disconnected on the latest #'s and test drives. It's a crane adjustable dialed back to about 8-10*. I just figured one less variable tracking down this noise.

 

Runs about 190-200 in stop and go around town, 180 thermostat. I could not find the UR5 in town (small town), but I could try the A.C. Delco equivalent

 

Set the initial way back to 4* btdc, to where the idle is rough. It's better, the rattle is a bit higher in the rpm and throttle range, and a bit quieter. Obviously not going to drive it around like this, but might be on the right path. I'll grab a set of those plugs. I greatly appreciate your time and help Larry!

 

No change with the R43TS. I bought a 160* t-stat that I will try in the morning, on this trip though it was 170-180*f

 

I have not been very agressive on the throttle for fear of hurting something. I know diagnosing via written words is near impossible, but it sounds like a can with rocks in it. At idle and quick revs in park it sounds great. I poked around with a long screwdriver as a stethoscope at idle, everything has a similar light sewing machine tick, aside from the alternator and bracket backing a lower grinding sound.

My only other thing I can relate it to is a spun rod bearing on a 94 Trans Am, with the noise as you float or let off the gas, definitely not that noise on the buick.

 

I think I'll disconnect the torque converter and give the flywheel another look. The bolts are snug, but maybe there is a crack under them. Running out of other ideas... All the engine and trans mounts are in good shape. Stock exhaust manifolds, no clearance issues

 

Flywheel and TQ converter check out fine, and the harmonic balancer does as well. I fetched a borescope from work (A&P Helicopter mechanic) so I'll stick that in the cylinders and wherever else it fits and see what I see..

 

Drivers side, nothing stands out in the cylinders, the pistons are dished with the triangle notch, looks just like these
https://www.summitracing.com/int/pa...-_-shopping-_-srese1-_-keith-black-kb-pistons

There is a good coating of carbon, which I think is due to the terrible edelbrock carb that had been backyard modified, on the car when i bought it

 

How good is the fuel in the tank?(sorry if this was discussed before, I didn't read the beginning of the thread)

 

About 6 weeks, new tank with efi pump and lines, topped off today with 8 gallons of fresh chevron 93 octane and about 10oz of seafoam leftover from another project

 

Looking at the plugs and what they tell you would have more validity than suspecting the ignition system type.
You might be able to see obvious signs of heat range issues as well as too much timing on the plug.
A good read would be to search "4 seconds flat plug reading" (?) . Good pics too.

I see now you have already addressed this but the plugs need to be visually inspected.

Another issue with a recently rebuilt engine is that the valve seats might be ground with an interference angle leaving very little contact width, or inadequate contact making the face of the valve run hotter.
I didn't catch it yet, but did the borescope show sharp edges in the combustion chamber?
Both of these issues 'could' make it difficult to curve a distributor without det. problems.
They could supercede a colder plug by being the initiation point of detonation.
Loose flexplate or crank bolts would also cause some noise, but the plugs or scope should show up obvious det. signs.