Weirdest engine rattle ever, BBC454. Help!

[Barbapapa]

Very strange - the noise is load-activated at certain RPMs but doesn't change pitch/frequencey with engine speed. Therefore, it almost can't be a rotating assembly, such as the flywheel or damper.

Zwede, here's some more random guessing and thinking out loud. Packard's comment brings up motor mounts, rear trans mount and also the differential mounting. Sorry for suggesting the motor mounts after you ruled them out but are you sure about the motor mounts? Weird things happen when the motor moves, lines and hose get tugged, maybe something around the radiator and electric fan? Apologies again but a good way to check the motor mounting is the leave the hood up, parking brake on and let the clutch out trying to load the motor as you peer at the engine looking for movement.

[jeff swisher]

Zwede i had a similar problem with a ford with an aod trans...sounded like the converter had broken parts in kind of your situation ...same pitch ..I replaced converter ...that did not help..It ended up being the little stop or washer on the starter between the drive gear and the nose cone.....That little sucker would tink tink tink against the flexplate only under certain situations like you stated ..

[allblowdup]

Have had a windage tray rattle like that once against the oilpan. Really weird noise.

[bill jones]

-Since the only thing you changed was to the hydraulic clutch---I'd wonder if you have totally ruled out throwout bearing getting tickled by the clutch fingers----like if the crank end play and maybe minimum throwout bearing freeplay are getting happy with each other.

-whatever you do---when you find the answer it'd be nice to hear the results of this ordeal.

[zwede]

Lots of excellent ideas. Thanks!

I did find a ripped motor mount and replaced it but no change in the rattle.

I also removed the oil pan and made sure the windage tray was tight and not close to anything.

I took a good look at the starter nose (removed splash shied). It's not near the ring gear.

The throwout bearing touching occurred to me. I lightly pushed the clutch in and the noise did not change. I figure with pressure on the pedal the bearing should spin with the clutch.

I will try to make a recording of it tomorrow.

Thanks again and please keep the ideas coming.

[Barbapapa]

Do you have inserts in the header collectors or sidepipes, auger type muffler/sidepipes? Thingies inside of the exhaust near the collectors are prone to coming loose and making mettalic rattles.

BTW, this thread is like a morning crossword puzzle at coffee time, we'll all miss it when you fix it but hope you do.

[zwede]

Very conventional exhaust system. 4-1 full length headers (hooker supercomp 1 7/8"), mufflers in the back, rear exit. No inserts, just a wideband O2 sensor in the collector. I checked that it's tight and the weld nut is secure (no cracked welds).

[ZEROMAN91]

I think your rattle is in the oil pan. I had the spot welds break on a corvette pan once and it made the same noise as you are desrcibing.

[Procision-Auto]

We'll have Zwede checking the colour of his floor mats before this
thread is done.

[SWR]

We'll have Zwede checking the colour of his floor mats before this
thread is done.

Hopefully they don't have a Western Diamondback pattern on them...

[Baprace]

As long as we are grasping straws on this very strange condition, HOW about the thrust bearing being worn and last but not least, fuel pump arm return spring or the pushrod that activates it ? Please keep us informed on this one..

[zwede]

Zeroman: I took the oil pan off and checked it. Couldn't find any bad welds and anything loose.

My floor mats are brown.

Baprace: I really hope the thrust bearing is OK as the short block was done by someone who seemed to really know his stuff.

The fuel pump is electric and mounted in the back.

I made a recording this morning. I'll check it tonight to see if it's any good (the microphone isn't the best).

[ZEROMAN91]

sorry about my post i missed where you said you took down the oil pan

[af2]

Have you reset or checked the lifter preload?
Had a similar one do that.

One other thing came to mind.
Did you check all the bearing clearances?
I had a small block 25 years ago that had been rebuilt with standard bearings and a .010 crank that had a similar sound also.

[SchmidtMotorWorks]

Does it run smooth and make good power?

A flat ex cam lobe can match some of those symptoms, even the frequency because it doesn't pop back into the intake on every 4 cycles.