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Mysterious sound. Completely stumped.


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Alright y’all... I’m usually not too bad at diagnosing the car, but this one has me completely and utterly stumped. First let me go through everything I’ve done, as some context might help.

This January, I pulled out the engine and changed the rear main seal, oil pan gasket, all the freeze plugs, and scrubbed the engine a bit to get some old gunk off. Then I changed the busted motor mounts and put the engine back in. I haven’t had much time, so it took me till last week to finally hook up all the wiring again and fire it up. The starter pretty much came apart when I tried to start the car; bunch of pieces of metal on the floor and it would just spin and not engage (crappy Duralast starter). I knew that was it. So I bought a gear reduction starter from Tuff Stuff and installed it today. Engine spun over beautifully. Added gas and she lit right up (timing is still off, but haven’t gotten that far). But along with a running engine, I got this loud chirping noise. And I mean LOUD. 

First thought was “belt” so I removed the drive belt (spins the water pump and alternator). That did nothing. Now I’m thinking the crank pulley is spinning and hitting a transmission line, but that’s not it either. Ok, what else could It be? The new starter? But it engages and disengages fine, doesn’t seem to keep starting after the initial fire-up or get stuck. At this point I’m starting to think I mounted the transmission incorrectly. I removed the inspection plate from the transmission and spun it... all the bolts are fine and nothing is scraped or looks off. I then realized I didn’t align the converter drain plug with the hole on the flexplate. Huge no-no, I guess I missed it while putting the whole thing together (the struggle of doing it by myself with a failing engine hoist definitely made me miss that little detail). So at this point, I started turning the engine over with my breaker bar and listened for scraping,  but it spun freely. I didn’t hear any scraping, at least nothing discernible. Still, maybe it could be that?
Here are a couple of videos where you can clearly hear that nasty chirping. Any guesses what it could be? 

Any help is greatly appreciated. It’s been one thing after another, and right when I’m seeing the light at the end of the tunnel, this happens. Thanks, everyone!

 

 

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What is your oil pressure?

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Posted (edited)

Oh right, I did forget to mention the oil pressure. I don't have an oil pressure gauge, so I removed one of the valve covers. Plenty of oil coming out.

And yes midlife, no belt up front. Only thing spinning was the crank.

 

Edited by BigBlue
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Its not as prevalent at high RPM, but gets worse as RPM's slow down, so I agree, a bearing outside of the engine on an accessory, or one thing you could check is the fuel pump arm/cam eccentric. I had a fuel pump once the the arm friction pad fell off and made a strange noise. Just something easy to check. Good luck! The rest of the car looks great!

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Posted (edited)

If you did not loosen and re-align the flex plate with the converter drain plug (you don't say you did), rectify that and eliminate that as a potential source.

Don't want to entourage running engine with that noise too often (damage is occurring somewhere) but using section of rubber tubing as stethoscope can narrow down the area the noise is coming from.

Edited by Bill73Ragtop
correction
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Posted (edited)

Sounds like something's definitely rubbing.   If you get to disassembling things now, i expect enough rubbing has occurred that you'd see a telltale mark.

I'd pull the starter and look for signs of damage.  Like maybe it wasn't fully disengaging.  Some starters are supposed to be shimmed when you install them.  Also pull the cover on the bellhousing and inspect everything inside for some new bare metal that shouldnt be there.

One of those mechanic's stethoscopes is worth its weight in gold.  https://www.harborfreight.com/mechanics-stethoscope-63691.html

Edited by giantpune
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I also had a similar sound years ago but it was the bearing on the alternator.   As you stated you have nothing external connected.  I would get a magnetic pick up tool and remove the inspection plate and pock it around and see if you pick up any metal shavings.  If non then I would remove the starter and inspect and check for any filings there.  As mentioned in the  post above you should be able to narrow it down to at least where in the engine it's coming from.   Good luck and I hope it's an easy fix for you.

Kilgon

 

 

"The only dumb question is the one not asked"

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Excellent suggestions from everyone. At this point my priority will be checking the flexplate/converter area as well as the starter. Odds are it’s in that area, as the rest of the engine hasn’t really been fiddled with much. May even get one of those stethoscopes at harbor freight to help me out. I’ll report my findings soon, hopefully this can eventually be of use to someone else. Thanks for all the help, guys!

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23 hours ago, BigBlue said:

I then realized I didn’t align the converter drain plug with the hole on the flexplate. Huge no-no, I guess I missed it while putting the whole thing together (the struggle of doing it by myself with a failing engine hoist definitely made me miss that little detail). So at this point, I started turning the engine over with my breaker bar and listened for scraping,  but it spun freely. I didn’t hear any scraping, at least nothing discernible. Still, maybe it could be that?

That's where I would start.  The flexplate will flex some but eventually break so you need to take care of the misalignment.  My guess is it's hitting the starter snout.

I had a weird knocking noise I couldn't find. I finally decided to check for a loose torque converter.  Here's what I found

Flywheel.thumb.jpg.8c313e59025e1c999cd0a3377b7c0dcf.jpg

 

Turns out when I pulled the tranny out I also pulled out and lost an alignment dowel. Just that little bit of play allowed around the trans to engine bolts was all it took.

Bob

 

Tachs, Voltmeters, Headlight kits, Wiper delays and more at

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Rocketman's Classic Cougar (and Mustang) Innovations, LLC

 

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Wow Bob, to think something so seemingly insignificant could cause such a huge effect. And here I am thinking that mayyybe I can get away with leaving the torque converter misaligned in the meantime :classic_rolleyes: lol 

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My vote would be something in the flexplate area.

I have found a stetoscope very useful to at least locate the are where the noise is coming from.

 

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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3 hours ago, Sheriff41 said:

I'm surprised no one has suggested the muffler bearing yet! :wrench:

No - that makes a whine.  I would lean more toward a loose wiggly pin in the wobbly shaft.

  • LOL 1

Kilgon

 

 

"The only dumb question is the one not asked"

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On first video I thought it was my wife when I do mustang stuff vs house stuff, but after carefully listening to the second, I could rule that one out... 

I don't think it's a rotating item, bits too irregular vs engine speed and vote as well for external non mechanical item. I'd start by checking engine mounts, then anything that can touch the engine, exhaust header a tad against PS gear would sing nicely... and follow exhaust on both sides after trans for clearance. as you have disconnected all on front, you could use a thick blanket and hear if that absorbs some sound, repeat per side.. 
 

73 modified Grande 351C. (Finally back on the road woohoo!) 

71 429CJ. ( In progress )

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On 5/28/2021 at 12:12 PM, Fabrice said:

I don't think it's a rotating item, bits too irregular vs engine speed and vote as well for external non mechanical item. I'd start by checking engine mounts, then anything that can touch the engine, exhaust header a tad against PS gear would sing nicely... and follow exhaust on both sides after trans for clearance. as you have disconnected all on front, you could use a thick blanket and hear if that absorbs some sound, repeat per side.. 
 

FWIW - On another car a long time ago, I had a similar sound from something rubbing on the frame. I don't recall the specifics but I was able to actually change the sound and ultimately locate it by using a prybar between the engine and frame and move it slightly and the sound would change. So I could see something like an engine mount, trans, exhaust or even one of the accessories rubbing the frame or body. 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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yeah, amazing how miss leading the sound of metal to metal can be.... Hope @BigBlue will find and tell us...

Wonder what the winner's price is too!

73 modified Grande 351C. (Finally back on the road woohoo!) 

71 429CJ. ( In progress )

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I guess it's a problem with your torque converter. A friend of mine has had it with his C4 few weeks ago. A part of the impeller was lose and blocked the torque converter during the starting process. That made the starter break off its seat. Then he had the same knocking/chirping noise I hear on your video. Finally the converter was scrap and the transmission needed a complete overhaul. The blocking which caused the drop off of the starter may have caused the losening of the dowel pin.

just my 2 ct.

Frank

1972 Mach 1, 351C-2V, wimbledon white, blue all vinyl luxury

born in Dearborn, grown in the district of San José, spent a lifetime in California, moved to Germany in 2010

Mustang_Mach1_wallpaper_300_150.jpg proud member of clublogozusammen.JPG.59fb4a10d15cfff9ec756235059135b8.JPG

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1972 Mach 1, 351C-2V, wimbledon white, blue all vinyl luxury

born in Dearborn, grown in the district of San José, spent a lifetime in California, moved to Germany in 2010

Mustang_Mach1_wallpaper_300_150.jpg proud member of clublogozusammen.JPG.59fb4a10d15cfff9ec756235059135b8.JPG

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Ok my turn to guess.

I thinks it coming from a rotating part and the reason it is amplified at the lower rpm, is because it’s slower friction point in generating a frequency that’s within our normal hearing range. As it rotates faster, we can’t hear it as well because it’s outside our hearing.

While that sounds far fetch to some, it may account for the why the volume and repetition do not seem to increase with the rpm. Now, what is it, could be 10 things. But, if I had to wager, I suspect the new starter, since it’s the only new part on the vehicle since the sound started.

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Sounds like a flex plate scraping to me.

kcmash

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  • 3 weeks later...

My WAG guess is flex plate not flat anymore or ring gear not "square" on flex plate. Chuck

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If your engine is a 351C, starter motors are different for automatic transmissions and manuals but bolt right up.  Not sure that is true for 302 engines or what engine you have.  Perhaps if the starter is for a manual it might cause the starter issues you had and maybe the scraping issue.   

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I like the guesses about the flex plate. I had issues with my flywheel rubbing after i assembled my engine. They can rub against the rear engine cover if the cover is not flat or fully seated.

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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