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12-13-2018
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#1 |
 
Join Date: Sep 2018
Location: Groton, CT
Posts: 373
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Slight knocking when cold
It's been fairly cold up here lately, 20-30 degrees.
My 92 has a knock for a while at startup until it gets up to normal water temp and normal oil temp. More pronounced while under load. Oil pressure is normal and not fluctuating, about 70 psi. Sounds like only one cylinder, not like the cold piston slap in my 5.3 Suburban. Once everything is warmed up, the knock goes away. Gets quieter as the temps come up. Car has 18,900 miles on it. So, is this normal, or should I be checking rod bearings?
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1992 ZR1 #442, 2 tops, White, White, Haibeck 415, 3.90 gear, Coilovers 2018 Audi RS5, 2.9 V6 Twin Turbo, Auto, Black, Black 2021 Audi Q3, 2.0T, 8 spd Tiptronic, Navarro Blue metallic, Pearl Beige |
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12-13-2018
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#2 |
 
Join Date: Jul 2007
Location: Bartlett, IL
Posts: 7,144
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Re: Slight knocking when cold
There is a knock or noise of chain slap at start, in cold weather idling I have heard piston slap. Can ou get a video with the noise you are hearing?
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1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978 |
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12-13-2018
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#3 | |
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Join Date: Sep 2018
Location: Groton, CT
Posts: 373
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Re: Slight knocking when cold
Quote:
I'll try to get a sound bite this weekend, but with just a cell phone for video, I'm not sure it will be too helpful..... I have no idea what LT5 chain slap sounds like.
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1992 ZR1 #442, 2 tops, White, White, Haibeck 415, 3.90 gear, Coilovers 2018 Audi RS5, 2.9 V6 Twin Turbo, Auto, Black, Black 2021 Audi Q3, 2.0T, 8 spd Tiptronic, Navarro Blue metallic, Pearl Beige |
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12-13-2018
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#4 |
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Join Date: Jul 2007
Location: Bartlett, IL
Posts: 7,144
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Re: Slight knocking when cold
You only should hear it for about a minute or less on a cold start. Knock could be piston slap or the dual mass flywheel too
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1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978 |
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12-13-2018
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#5 |
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Join Date: Sep 2018
Location: Groton, CT
Posts: 373
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Re: Slight knocking when cold
This noise lasts a lot longer than a minute or two. More like 5 to 10 minutes.
I'll be pulling the pan either this weekend or next to replace the leaking gasket. I'll see if anything wiggles excessively while I'm in there....
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1992 ZR1 #442, 2 tops, White, White, Haibeck 415, 3.90 gear, Coilovers 2018 Audi RS5, 2.9 V6 Twin Turbo, Auto, Black, Black 2021 Audi Q3, 2.0T, 8 spd Tiptronic, Navarro Blue metallic, Pearl Beige |
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12-13-2018
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#6 |
Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,852
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Re: Slight knocking when cold
It may very well be the dual mass flywheel if the engine is running rougher at that temperature. Those temperatures can affect the coils, wires and injectors if they are marginal to begin with. This results in the engine running rough and imbalanced which in turn causes the dual mass flywheel to knock. That’s where I would look first. Bearing problems on LT5’s are very rare especially with those low miles. These engines are known to exhibit piston slap when cold however that should go away within a minute or two depending on the temperature. No reason to be too concerned at this point.
H 
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90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold. |
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12-13-2018
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#7 |
Join Date: Mar 2015
Location: New Zealand
Posts: 382
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Re: Slight knocking when cold
You should try tightening the bolts on the oil pan a friend did and stop the oil leak on his Z
Sent from my SM-G960F using ZR-1 Net Registry mobile app |
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12-13-2018
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#8 | |
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Join Date: Sep 2018
Location: Groton, CT
Posts: 373
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Re: Slight knocking when cold
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Bolts were tightened once already, still leaks. Also going to check the Oil Pressure Regulating Valve Cover Plate.
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1992 ZR1 #442, 2 tops, White, White, Haibeck 415, 3.90 gear, Coilovers 2018 Audi RS5, 2.9 V6 Twin Turbo, Auto, Black, Black 2021 Audi Q3, 2.0T, 8 spd Tiptronic, Navarro Blue metallic, Pearl Beige |
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