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Help me identify this engine noise..
1970 911t, engine rebuild about 6 years ago. Just last week this rhythmic sort of rubbing engine sound started. There at idle and increases with revs. No change in performance. Coming from fan area so assumed it was the fan rubbing on the housing. Removed the pulley and belt and fan seems to spin fine. No cracks on shroud. Can alternator make this sound? Any other areas to look? Hope the video helps. Thanks.
https://youtube.com/shorts/xJYv4shA4_Y?feature=share
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1970 911T/S coupe Irish green 2013 991 coupe aqua blue sold 1978 911SC Targa Venetian blue/cork sold 
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09-24-2024, 05:23 AM
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Run the engine for a short time [30 seconds] without the belt to rule out a problem with the fan etc.
Quote:
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"But instinct is something which transcends Knowledge We have undoubtedly certain finer fibres that enable us to perceive truths when logical deduction or any other wilful effort of the brain is futile" Nikola Tesla |
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09-24-2024, 05:41 AM
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Senior Member
Join Date: Sep 2001
Location: Chesapeake, VA
Posts: 1,699
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Almost sounds like you have a spark plug that is loose...
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Chris 1988 911 Carrera Targa (driving project started JAN 2022) 1970 911E - Long since gone 1972 911 Targa - gone 1987 911 Carrera - gone Retired FA-18C Driver |
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09-24-2024, 05:51 AM
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Now in Florida !
Join Date: Aug 2012
Location: York Beach, Maine and Anastasia Island, Florida
Posts: 406
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Agree that it sounds like a compression leak.
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1983 911SC Coupe Hot Rod - Platinum - Twin plugged 3.4, DC-60 cams, PMO 50's, 1 3/4 headers, Bill Rader 915 w/LSD 1976 914 2.0 Lime Green Metallic - Completely stock |
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09-24-2024, 07:09 AM
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After listening to it again, It does sound like a loose spark plug, or maybe [hopefully not] snapped head studs ?
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"But instinct is something which transcends Knowledge We have undoubtedly certain finer fibres that enable us to perceive truths when logical deduction or any other wilful effort of the brain is futile" Nikola Tesla |
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09-24-2024, 08:54 AM
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New-ish 911SC Targa Owner
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did the 1970 911T have the smog pump ports on all the cylinder heads? if they were "plugged", perhaps one plug has rattled out. Would be the same noise as a loose spark plug.
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'83 Targa 300k w/ freshened 3.0 with 930/52 case# 6770540 ARP and Raceware hardware - AEM Infinity 506, Triumph T595 ITBs, B&B headers, Dynomax muff, Fidanza FW, Alum PP-203whp |
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09-24-2024, 08:59 AM
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Great advice.
I'll run the engine briefly with the belt off. I can try to check if any of the spark plugs are loose assuming noise continues after belt off. I'm not sure about the smog pump. I don't think so. Pulley only has one groove for one belt but regardless I'll look into that too.
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1970 911T/S coupe Irish green 2013 991 coupe aqua blue sold 1978 911SC Targa Venetian blue/cork sold
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09-24-2024, 09:20 AM
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I think the cadence of the noise rules out the fan. Sounds like a rocker, or compression leak, possible broken head stud ( ?) Difficult to determine based on the audio.
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'77 1973 911RS Backdate, 2.7 liter w/webers '70 911ST , 3.2 liter '82 '74 911 IROC Tribute , 3.0 in progress '75 911 RSR street car in progress '77 930 Replica '75 993 GT2 EVO race car , 3.6 TT '79 928 5 speed money pit in progress |
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09-24-2024, 10:42 AM
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I think smog pumps ( air pump) were on the later models, beginning in '74 . Could be mistaken.
I would check compression on all cylinders as a starting point.
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'77 1973 911RS Backdate, 2.7 liter w/webers '70 911ST , 3.2 liter '82 '74 911 IROC Tribute , 3.0 in progress '75 911 RSR street car in progress '77 930 Replica '75 993 GT2 EVO race car , 3.6 TT '79 928 5 speed money pit in progress Last edited by pocv0; 09-24-2024 at 10:48 AM.. |
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09-24-2024, 10:46 AM
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Sounds more mechanical to me. I'd start by removing the valve covers and check head studs and rockers. Do a valve adjustment while you're in there.
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Walt 82SC 3.0 81SC 3.6 |
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09-24-2024, 11:04 AM
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Ok. For what its worth when driving at speed its less noticeable but maybe thats just a frequency thing.
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1970 911T/S coupe Irish green 2013 991 coupe aqua blue sold 1978 911SC Targa Venetian blue/cork sold
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09-24-2024, 11:19 AM
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Join Date: Nov 2023
Location: Kent, UK
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Just a note. If you decide to do the valve adjustment, this must be done with the engine stone cold.
In case you didn't already know. Hope this helps. |
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09-24-2024, 01:52 PM
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PCA Member since 1988
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Quote:
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1973.5 911T with RoW 1980 SC CIS stroked to 3.2, 10:1 Mahle Sport p/c's, TBC exhaust ports, M1 cams, SSI's. RSR bushings & adj spring plates, Koni Sports, 21/26mm T-bars, stock swaybars, 16x7 Fuchs w Michelin Pilot Sport A/S 3+, 205/55-16 at all 4 corners. Cars are for driving. If you want art, get something you can hang on the wall! |
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09-24-2024, 03:12 PM
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Ran without the belt. Definitely not the fan.
Don’t have the toolkit so I’ll order the spark plug socket and check that next. If not that then move onwards and remove valve covers.. And just did oil change… Hope I can figure this out before Fall driving season is over. Just got the wheels tires and suspension sorted out too. |
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09-24-2024, 03:20 PM
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PCA Member since 1988
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nhs15: If you don't have the toolkit that came with the car, try to replicate one (without spending $1500!). The spark plug tool that came in any of the 911 kits is exactly the right length to reach the plugs past the sides of the engine bay, and it is knurled on the outer end to that it's easy for you to grab and spin with your thumb and fingers.
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1973.5 911T with RoW 1980 SC CIS stroked to 3.2, 10:1 Mahle Sport p/c's, TBC exhaust ports, M1 cams, SSI's. RSR bushings & adj spring plates, Koni Sports, 21/26mm T-bars, stock swaybars, 16x7 Fuchs w Michelin Pilot Sport A/S 3+, 205/55-16 at all 4 corners. Cars are for driving. If you want art, get something you can hang on the wall! |
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09-24-2024, 04:06 PM
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gduke2010
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bump, back to the top
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09-25-2024, 06:55 PM
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Quote:
Ivan
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1985 911 with original 501 761 miles...807 506 km "The difference between genius and stupidity is that, genius has its limits". Albert Einstein. |
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09-26-2024, 12:07 AM
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Well the spark plugs all seemed tight. Valve adjustment next?
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09-28-2024, 06:27 PM
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interesting..can you make another video from the front of the engine and moving slowly side to side..or even from the bottom? How about loose heads?It really sounds like puffing..
Ivan
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1985 911 with original 501 761 miles...807 506 km "The difference between genius and stupidity is that, genius has its limits". Albert Einstein. |
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09-28-2024, 11:40 PM
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https://youtube.com/shorts/dkzO3Rn23TU?feature=share
https://youtube.com/shorts/TS0mNsOdXpQ?feature=share https://youtu.be/-DukRGWVD30 https://youtu.be/4l2zDb7pA6E
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1970 911T/S coupe Irish green 2013 991 coupe aqua blue sold 1978 911SC Targa Venetian blue/cork sold
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09-30-2024, 09:49 AM
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1985 Porsche 911 3.2 Carrera Sport
Jeanine
1985 Porsche 911
2011 BMW 550i
