"Interesting" metallic, rhythmic engine noise - Alfa Romeo Bulletin Board & Forums

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post #1 of 13 (permalink) Old 03-19-2017, 06:20 PM Thread Starter
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Question "Interesting" metallic, rhythmic engine noise

Hello knowledgable and experienced ones,

I recently posted about a cracked 1-4 exhaust manifold and a noise coming from the engine that I thought was caused by that faulty part. the sound has been present in my '91 Spider since I bought it last September but has gotten more prominent over the past 4 months. Though I have read on these pages that a cracked manifold CAN produce a flickering metallic sound, I'm really thinking that something else is causing it.

At first I thought it was a valve shim problem but as I listened today, it sounded as though it was coming from the front of the engine - near the pulleys. It does sound metallic but also "brassy" and "tinky." When the engine idles there's just a hint of the sound but as I rev up the engine it increases with the speed of the acceleration. As I listen again to the attached video, it almost sounds like a belt noise. When I'm crusing it is intermittently constant - that is, it rings for a few seconds, quiets of a few seconds and then starts up again, over and over again in that kind of series, all in a steady rhythm. It is quite noticeable standing outside the car and when sitting in the cabin. Oil pressure, engine temp, power and acceleration don't seem to be affected. It's mainly annoying and must be signifying that something isn't right.

Anybody have ideas? Water pump? - documentation says it was replaced in 2014. Belt? - also replaced then. Actually, it sounds even more metallic in person.

This video I uploaded to Youtube will take you there. www.youtube.com/watch?v=aVUzGu_QCTg

Last edited by rjlowden; 03-19-2017 at 06:27 PM. Reason: Just changed a couple of words in the last paragraph.
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post #2 of 13 (permalink) Old 03-19-2017, 07:18 PM
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Have you replaced the cracked manifold?

1969 1750 Spider Veloce w/dual webers, 1969 1750 Berlina, 1971 1750 Spider Veloce w/ dual webers, 1985 Spider Veloce 23,000 orig. miles, {Two} 1986 Spider Veloces, 1987 Spider Veloce bought new, 1988 Quadrifoglio, 1991 164S, Plus several more. I think they are breeding.
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post #3 of 13 (permalink) Old 03-19-2017, 07:31 PM
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Get a mechanics stethoscope and start checking stuff.

Tom

1991 Spider
1963 Giulia Spider (1750 engine)
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post #4 of 13 (permalink) Old 03-19-2017, 07:35 PM Thread Starter
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No, unfortunately the one I ordered from Centerline didn't fit so we had to reinstall the old one but with new gaskets and bolts. I'm on the trail for another but they're hard to find.
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post #5 of 13 (permalink) Old 03-21-2017, 03:06 AM
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that engine wobbles too much for my liking...so, possibly the crank pulley rubbing intermittently on sway bar as you rev and the engine wobbles and contacts....bad mounts I'm guessing?

Photo shows mine was just starting to rub (a feeler gauge might have fitted in there, just!) when I noticed the shot engine mounts.
New engine mounts and now my fingers fit between the gap!

PS: old photo so that gungy oil is gone, and the slightly frayed belt is changed
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Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.

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post #6 of 13 (permalink) Old 03-21-2017, 07:44 AM
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I used to have a late 70's spider that had a sheet metal heat shield tack welded to the downpipe below the exhaust manifold. I don't know if your '91 has something similar. A few of the tack welds fatigued over time, allowing the shield to vibrate at certain RPM's. The sound would be like what you describe: a metallic ringing.

My loose heat shield caused no harm, other than driving me nuts. I eventually used a chisel to break the other tack welds, and lived without the shield. Of course, a new part would have been a better solution.

Jay Mackro
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'65 Guilia Sprint GT
'67 Duetto
'91 164L

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post #7 of 13 (permalink) Old 03-21-2017, 09:54 AM
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FYI
Original Alfa Romeo Spider 2,0 Krümmer / Auspuffkrümmer 115880170500 | eBay

can't think there'd be a difference to euro and USA manifolds and not the cheapest part (these guys never are) and in Germany......but if all else fails worth keeping in mind I suppose!

Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.
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post #8 of 13 (permalink) Old 03-21-2017, 10:09 AM Thread Starter
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Thank you all for your input. I'll check out that possible crank pulley rubbing as well as the heat shield. My stethoscope arrives tomorrow; that may help locate the sound. I'm also thinking about taking the car over to the Nick Falcone shop near Philly to have a few things checked out.
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post #9 of 13 (permalink) Old 03-21-2017, 12:46 PM
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I think your going to find that its the exhaust leak.

FYI. The 91 and later exhaust manifolds are slightly different from the standard 2 pc factory headers. Alfa had to curve them a little differently to clear the power steering.

1969 1750 Spider Veloce w/dual webers, 1969 1750 Berlina, 1971 1750 Spider Veloce w/ dual webers, 1985 Spider Veloce 23,000 orig. miles, {Two} 1986 Spider Veloces, 1987 Spider Veloce bought new, 1988 Quadrifoglio, 1991 164S, Plus several more. I think they are breeding.
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post #10 of 13 (permalink) Old 03-21-2017, 04:50 PM
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A mechanics stethoscope is some of the best ten bucks or so that I've ever spent.
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The passenger seat is 15 miles an hour faster than the drivers seat.

currently
74 GTV restored daily driver
71 Berlina in resto
the ones that got away:
1959 750 series Giulietta Spider Veloce
1962 Giulietta Spider normale
1965 Giulia Sprint normale
1972 GTV
1974 GTV
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post #11 of 13 (permalink) Old 04-03-2017, 07:56 PM
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Theres a set of S4 manifolds on ebay. Decent price also.


1992 Alfa Romeo Spider Exhaust Manifold with Heatshield | eBay

1969 1750 Spider Veloce w/dual webers, 1969 1750 Berlina, 1971 1750 Spider Veloce w/ dual webers, 1985 Spider Veloce 23,000 orig. miles, {Two} 1986 Spider Veloces, 1987 Spider Veloce bought new, 1988 Quadrifoglio, 1991 164S, Plus several more. I think they are breeding.
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post #12 of 13 (permalink) Old 04-03-2017, 08:11 PM Thread Starter
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Yep, looks like it IS one. I believe I'll bid. Thanks, Jim.
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post #13 of 13 (permalink) Old 04-10-2017, 01:41 PM Thread Starter
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The sound is gone! Vince Votto, the Master Mechanic at Nick Falcone in Bala Cynwyd, PA replaced the belt that ran the A/C and the alternator and it was no more. What a difference. The air conditioning is not working for a different reason but we'll take care of that later. It turned out to have nothing to do with the manifold. By the way, I did bid and win the '92 manifold on eBay. It includes the entire set of 1-4, 2-3 and two heat shields. Hoping for the best. Thanks, Jim G. for pointing me in that direction.
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