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Canadian Poncho Homepage -> Canadian Poncho -> General Engine Performance Forum -> A metallic rattling sound, heard at around a steady 2500-3000 RPM. Any ideas?
Post Info TOPIC: A metallic rattling sound, heard at around a steady 2500-3000 RPM. Any ideas?
cdnpont


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A metallic rattling sound, heard at around a steady 2500-3000 RPM. Any ideas?
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For some time now, when driving on the highway. at between, say, 65 to 75 MPH I'm hearing a metallic rattle or clatter like sound coming from my HO350. It can be heard coming through the firewall, and it sounds like its at the rear topside of the motor. It has a somewhat random pattern to it.

It varies with load. When applying load at highway speed, or coasting down, it fades away. Steady state cruise is when it's the loudest. You can make it come and go depending on load. It can seem louder if the engine isn't yet up to temp, and fades somewhat after a long drive. It's not super loud, or loud enough to scare me yet, but it's there and it's not getting any better! It's never heard around town.

I haven't rechecked my lash since the engine went in, but the engine idles without even the slightest hint of ticking or any lifter noise. Lash was the first thing that comes to mind.

I see 40 psi oil pressure at highway speed. 15-20 at idle depending on temp.

Am I hearing piston slap, or a possible rod knock? A loose rocker? I've never had a SB go bad....could this be the beginning of my stroker build?

Any Ideas?



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Captain Beaumont


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That's the sound of loonies and toonies exiting the gas tank

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4SPEED427


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Cracked/broken flexplate?

I had one once on a 283 that made strange sounds. However, I had a pretty lumpy idle and it was obvious at idle as well.

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beaucarlo


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wrist-pin ?

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bob lewis
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beaucarlo wrote:

wrist-pin ?

 A few years back, I tore down my brother in law's 454 for a similar noise and also a low miler. Turns out a cam lobe wore down and the filings worked they're way into the wrist pin causing it to stick. Got to use the proper cam break-in additive these days. 



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4SPEED427


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You've got a dash cam, will it be audible if you make us a video?

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Carl Stevenson wrote:

You've got a dash cam, will it be audible if you make us a video?

 Technology! You got to like it! smile



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66 Beau


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Here's a wild shot, but my 350 HO came with air cleaner. Turns out the stock accelerator linkage just touched the bottom of the air filter housing at certain points. Created an annoying rattle that I finally discovered by accident.

Worth checking anyway ...

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cdnpont


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Carl Stevenson wrote:

You've got a dash cam, will it be audible if you make us a video?

 I don't think the dashcam mic would be good enough to pick it up, but I do have a video camera, an I phone and a nice Nikon camera that shoots movies! I'll hook them all up and let the best one win! I'll try a recording tomorrow maybe.

 No heat riser, and the sound is not like the ringing of a piece of sheet metal on something else. It's a distinct metallic clatter or clack. Like a lifter with too much clearance, or a loose rocker. Not a knock so to speak. Problem is, it's only heard above 2500. The flywheel should be looked at for sure, and I'll have a good listen while revving it parked up through 2500. I'll pull the rocker covers and check the rockers. I know it's easy to be fooled by sounds...but it really does sound internal.

Not too worried as she'll be put away shortly. I'd like to go through and improve this motor at some point, weather that happens sooner than expected, that's fine, but it would be nice to have something not trashed to build off of.

Thanks guys! Keep the suggestions coming!

 



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cdnpont


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66 Beau wrote:

Here's a wild shot, but my 350 HO came with air cleaner. Turns out the stock accelerator linkage just touched the bottom of the air filter housing at certain points. Created an annoying rattle that I finally discovered by accident.

Worth checking anyway ...

 Absolutely! Worth checking everything!



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694279


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i had a big block chev would only do it at 2,000 grand wore out lifter bore

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427carl


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Check the air breather   might be touching 



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cdnpont


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I made a recording off my iphone today at highway speeds, and it sounds awful, pretty cringeworthy at a couple of points. To my ear, I picture a lifter rattling on a lobe, or a loose rocker.

Could it be a collapsed lifter, a bad lobe, bad spring or a simply a rocker out of adjustment? Problem is, it idles without even a hint of ticking. Smooth as can be.

I'll post the sound byte tomorrow.



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cdnpont


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Here's the clip. no

Advance to 1:20 where the fun begins. RPM varies from about 2500 to 4000.

At around 4:20 I put a good load on it starting up a hill.

At idle,

 



-- Edited by cdnpont on Saturday 19th of October 2013 01:14:31 PM



-- Edited by cdnpont on Saturday 19th of October 2013 02:53:20 PM

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66 Beau


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I can't tell - is the rattle speed-sensitive or RPM-sensitive. Almost sounds speed-sensitive and not RPM.... I agree too - sounds more like a bracket or exhaust rattling. Might just be the recording.




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cdnpont


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I think its RPM sensitive, above around 2300 it's really always there in some form, although adding or taking away the load can make it come and go in volume.



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beaumontswanted


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A jumping ignition from coil will sound like that, but just not as loud. A cut open oil filter is good assurance nothing is wrong with moving internal engine parts.



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68 327 4spd


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Sounds like flywheel to me.

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JERICO


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Flywheel bolts loose? Like Carl said, cracked flex plate?



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