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930s rule the wasteland
 
h20cooled7's Avatar
 
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dull knocking noise at hot idle?

is a dull knocking noise at hot idle normal? oil level is on the money and was changed recently. the noise seems to be intermittant, it wont doesnt happen when the car is cold. is this the air pump possibly?should i start saving for a rebuild?
pete
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1980 930 Turbo
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1983 944
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Old 02-03-2007, 01:32 PM
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Buy a stethoscope and trace it.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 02-03-2007, 02:41 PM
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I have seen so many different things cause this. Worn bearings, wrist pins, piston slap, even valve train noise. I wouldn't run just yet but I would start listening and looking at the oil to see if you have bearing wear, loss of oil pressure and so on. You will find that a certain amount of slap is common with these cars and more noticeable at temps because the oil thins out and isn't as much as a buffer.

Piston slap can wear rings faster but not life or death. The RUF short skirt pistons slap so bad you think you lost a bearing! But considered normal.

Without hearing the motor I can only offer suggestions.
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Old 02-04-2007, 09:02 AM
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can i notice bearing wear by smearing the dipstick on a white sheet of paper? when should i start looking to rebuild? the car runs fantastic. the carrera tensioners have not been done ,would this be my noise?
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1980 930 Turbo
1993 Corrado
1983 944
1984 944
2001 VW golf TDI
Old 02-04-2007, 09:10 AM
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What is your idle speed. FWIW, my 87 930 had the same symptoms. When cold, everything was great, however, when it got hot, it had a dull knock as you described. I took it to my mechanic and he told me that if the idle is below spec on some turbos, the intermediate shaft will sometimes make noise. In fact, my idle when hot was around 750 rpm. As he raised to idle up to around 900 or 950 rpm, the sound completely went away. No more issues.

Mike
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Old 02-05-2007, 07:32 AM
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Not really. You would want to send it in and have an analysis done then do it often to look to see if any levels are going up.

Chain tensioners can also make this noise. This is why it is important to determine where the noise is coming from first.
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94 3.6Turbo 6-speed AWD
Old 02-05-2007, 07:43 AM
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Get a stethoscope. I was amazed how good it was at locating noise. I only got a cheap one.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg

Last edited by NathanUK; 02-05-2007 at 09:31 AM..
Old 02-05-2007, 09:28 AM
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