Thread: chevy small block 355 metallic sound

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I have recently rebuilt a chevy 350.

Specs:
bored .30
dart 2.02 heads
1.6 summit rockers
lunati cam Gross Valve Lift (Int/Exh): .489/.504
RPM high rise intake
670 street avenger carb
Street fighter distributor MSD
forged pistons 4 valve relief
forged rotating assembly
clevit bearings all around

hp rebuild kit on tranny, new clutches, bands, you name it.
racing performance shift kit.



So i started it up to break it in like normal, ran perfectly fine, no rattling or any noise. so the break in was complete. I changed the oil with 10w30 valvo. dumb mistake, should of used rotella. But any ways. I drove it about 20-50 miles. i noticed this metallic weird ass rattling noise. It only appears when the motor is starting to get warm. and when you reeve it up, it doesn't get loud but when the motor comes back from a high reeve to a low idle, it starts to make a major rattle noise. Very metallic, very random noise. Well i took my timing cover off to check if my camshaft bolts backed out, they haven't and everything looked like it should. When it's idling i can hear it in the engine bay but not under the car. strange, right? the oil is fine and coolant looks fine. I've rebuilt a few motors, mainly mopars, 440's and i did a 12 valve cummins. I never heard this noise in my life besides when my friends truck had camshaft bolts backing out and it started to grind on the timing cover. The flex plate is tight along with torque converter. all my rockers move how they should when running. My friend thinks it's my turbine in my torque converter going out. but wouldn't i hear it under the car verses above the car?

I would wonder about valve lash. It would come from the top, but of course from valve covers.
How was the timing chain?

take off the valve covers and watch the pushrods as its idling/rattling-----if any pushrods aren't spinning, its wiped out the cam lobes/lifter bottoms


also if sound is from back of block---loose flex plate, torque converter, flex plate on backwards, maybe even stuck starter drive

Did you put the flywheel cover back on? I have put them on bent and they make a very metallic sound.

I figured the problem out. I pulled the motor today and i noticed my front main bearing was smashed. the crank would wobble at a certain rpm and go away. ordering a new crank and gasket set. i'll post pics of the mains when i tear the motor apart. I could tell it was smashed after i took the timing sprocket off.

Originally Posted by t-top havoc

I would wonder about valve lash. It would come from the top, but of course from valve covers.
How was the timing chain?

timing chain was loose a little. I grabbed the front of the crank and pulled up and the chain got more slack in it. so i pulled the motor. and i seen that i flattened my main bearing.

So i got done taking the motor apart. all crank was basically grounded down by the mains, mains are complete shot, and the crank is too. It was like a monster clawing its way out. the whole crank wobbled.

So are you saying the crank was bent, and that caused it to chew up the main bearings? I don't understand "...basically grounded down by the mains".

Originally Posted by rspears

So are you saying the crank was bent, and that caused it to chew up the main bearings? I don't understand "...basically grounded down by the mains".

the crank wasn't manufactured correctly. crank is cast steel, powered metal. if you don't get the metal at the right temp it will be like butter. in this case, my crank was butter. you can take a needle and slide it across the journal and it'll put a decent scratch in it. took it to my machinist. he tested it. eagle is junk along with cast cranks. bought a forged steel 4340 scat crank this time.

also, exact same words he said, "the mains bearings should of lost, but in this case, the crank lost." my main journals are shot complete, it actually shaved them all down so my crank would wobble on my main bearings.

Was this a new Eagle crank? I'd think that Eagle would stand up to the failure, but then you didn't want another one so it's a moot point. Since you had all of those crank particles circulating in the oil are you doing a total tear down/flush before dropping the new SCAT crank in there?

I would give you odds that the main bearings were installed wrong and/or oil galley plugs

I didn't know they still metalized cranks heard of it back in the 70s but thought it went by the wayside.??? OH and NEVER used one

Would love to see some pictures - if the tolerances were that loose there must have been zero oil pressure? How do the rods look? Is everything blue in color from extreme heat? You may have a completely toasted engine on your hands..