Yikes, this noise!

[Berlinvet]

Good day everyone. After perusing this forum for a while it’s time to ask directly about a problem I’ve encountered with my 327 SBC.

Backstory: recently I bought a 1968 C10 Fleetside LB 327 with a TH400 from an acquaintance. The truck had overheated on the highway but limped to a storage shed here in San Antonio. That was 18 years ago. The PO had rebuilt the engine to some extent, including a bore out. However he’s not too sure what else was done apart from piston rings and a few other basics. After evicting all the rats that had made a home in the cab I replaced the fuel tank,added inline fuel filters and installed new radiator and hei ignition. Oil levels looked good and eventually the engine fired up. After turning over by hand and leaving 10cc of Marvel Oil in each cylinder for a week. Changed the oil then. First big issue was a failing fuel pump diaphragm and copious amounts of gasoline in the engine oil. Instead of 5 quarts I must have drained about 10 quarts of oil-fuel mix. Replaced fuel pump and resolved the issue. Exhaust manifolds were both cracked and replaced. Topped up transmission fluid and took her out and back into the garage.

Next time the engine was started I noticed a grinding metal on metal sound that appeared to originate from the back and lower need of the engine. Scraping metal on metal with lots of friction would aptly describe it. Upon closer inspection the sound, which increased in intensity and pitch with increasing rpm appeared to come from the vicinity of the oil pan/starter/torque converter. Flywheel clearance to starter is within spec.

Transmission was pulled, torque converter removed flywheel inspected. Flywheel appears firmly bolted, doesn’t oscillate. The grinding noise is now gone but there is still a knocking banging noise coming from the back of the engine right above the oil pan.

Plan: install new torque converter and see what happens. Need to get brake lights to work then she’s ready for inspection. Not sure what’s going on or how to proceed with diagnostics. Any ideas?

[Grumpy old man]

post a you tube video and link it here so we can hear it .

[Berlinvet]

Pic

[garyd1961]

Could be a cracked flexplate/flywheel or either a main bearing spent. I would check the flexplate first.

[Berlinvet]

Flexplate seems to be ok. Didn’t see any cracks, backed out bolts. It’s still on the engine and when running doesn’t wobble or anything.

[Steeveedee]

With the engine off, slightly tweak the flex plate front to back and listen for any creaking, at a few locations. With that much dilution of the oil, if it was driven like that it could now have a spun rod bearing.

[Mikes68C10]

Originally Posted by Berlinvet

The grinding noise is now gone but there is still a knocking banging noise coming from the back of the engine right above the oil pan.

Sounds like you need to pull the oil pan, and check connecting rods/main bearing caps for excess play, sounds like a spun connecting rod bearing, giving that banging noise is the connecting rod being smacked around on the crankshaft.

Back in the early 80's a friend and I went through 3 short blocks in his 67 Camaro from Friday night through Sunday night, we had swapping engines down to a science, with each successive engine ending in a glorious loud final bang and a connecting rod (or remains of one) hanging though the side of another SBC (283's) or through the oil pan... yeah, I've hear that banging sound before

[AussieinNC]

To test for a spun rod bearing, remove the spark plug wire from one of the rear cylinders and start the engine...

If the noise is the same, shut down the engine, replace that spark plug wire and remove the other side rear spark plug wire and restart the engine...

The noise will not be as violent or harsh when the cylinder affected is not firing.

If the noise drops in level...(it wont totally disappear)...you have a spun rod bearing and the engine will need to come out...

Most likely scenario was the original failure of the fuel pump diaphragm allowed fuel to enter the oil pan, diluting the oil and causing the rod bearing failure.

[cornerstone]

Nice truck! Great colors.

[Berlinvet]

Thanks for all the replies. Will attempt above measures on Tuesday and I'm really hoping the engina can stay where she is....