Noise in engine????
Thread Starter
Pro
Joined: Jun 2004
Posts: 546
Likes: 25
From: NASHVILLE TN
Noise in engine????
I know this has probably been covered before, but what is the "tapping" noise at idle when you first start a C5. I have had several and they all do it. My brother has a 97 and it also does it. It starts shortly after cranking it up and gets louder until it warms up. I heard the same noise on all of the coupes I have owned, but did not hear it on my Z06. I have heard a brand new Vette at the dealer do the same thing. My brother has questioned the dealer about this and they say it is a normal noise and can't be fixed????? Seems funny that a brand new car should have engine noise. Just wondered what the fellow Vette owners thought of this and if their cars do this also. Thanks for the input. 
Thread Starter
Pro
Joined: Jun 2004
Posts: 546
Likes: 25
From: NASHVILLE TN
Yeah, that is what they told my brother. I wonder why I don't hear it on the Z06? You would think they could correct the problem since it was there all the way back in 97. Wow. Does your car do it also?
Team Owner
Joined: Sep 2001
Posts: 23,283
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From: Lake Elsinore, CA
It's not just C5's that do this. Many GM vehicles do it and, in fact, it can occur in any piston engine given the right circumstances. GM has attempted to address the problem of piston slap or "cold piston knock" by coating the piston skirts with a polymer and tightening the piston-cylinder bore clearance.
From Hib Halverson's "Relentless Pursuit of Power: The Sequel"
"When you decrease the piston-to-bore clearance, you’re more susceptible to hot-scuff because you’ve got a tighter fit. The coating gives us resistance against scuffing," Juriga stated. When asked about possible power losses, he added, "We haven’t seen any measurable hit from a power standpoint because of the tighter clearance."
The LS1/LS6 are first in the Gen III family to use coated pistons. Corvette often leads the way with new technology that eventually sees high volume production. In the near future, all Gen IIIs used in GM trucks will have coated pistons–we’re talking millions of engines a year, here, not just 90,000 or so C5, Camaro/Firebird and export (to Holden’s in Australia) powerplants annually.
This piston knock anomaly that has been occurring in some ’97-’01 engines after start-ups in cold weather is not a durability concern. It’s a pleasability issue on which there was enough input from customers that GM made a production change. Like the revised rings, there’s no performance advantage in switching to the tighter clearance and the polymer-coated piston. Those hearing a cold piston knock are better off ignoring it until the engine warms a little, rather than subjecting themselves to the stress of a dialog with a GM dealer intended to force repair or replacement of the engine.
From Hib Halverson's "Relentless Pursuit of Power: The Sequel"
"When you decrease the piston-to-bore clearance, you’re more susceptible to hot-scuff because you’ve got a tighter fit. The coating gives us resistance against scuffing," Juriga stated. When asked about possible power losses, he added, "We haven’t seen any measurable hit from a power standpoint because of the tighter clearance."
The LS1/LS6 are first in the Gen III family to use coated pistons. Corvette often leads the way with new technology that eventually sees high volume production. In the near future, all Gen IIIs used in GM trucks will have coated pistons–we’re talking millions of engines a year, here, not just 90,000 or so C5, Camaro/Firebird and export (to Holden’s in Australia) powerplants annually.
This piston knock anomaly that has been occurring in some ’97-’01 engines after start-ups in cold weather is not a durability concern. It’s a pleasability issue on which there was enough input from customers that GM made a production change. Like the revised rings, there’s no performance advantage in switching to the tighter clearance and the polymer-coated piston. Those hearing a cold piston knock are better off ignoring it until the engine warms a little, rather than subjecting themselves to the stress of a dialog with a GM dealer intended to force repair or replacement of the engine.
Le Mans Master
Joined: Jun 2004
Posts: 6,269
Likes: 50
From: Dallas Texas
St. Jude Donor '06-'07-'09-'10
Dayamn Patches, you are a fund of information. What happens when the coating wears off. Tried Telfon coated racing pistons years ago, but it didn't stick. No question Hi Performance engines like clearance and you don't hear all the piston and valve train noise over an open exhaust, but it becomes a trade-off on production street cars. 
Instructor
Joined: Jun 2004
Posts: 137
Likes: 0
From: Grand Ledge MI
I was told by one of the largest Corvette dealers in Michigan that this tapping noise is coming from the fuel injection system and is common in the C5's. Since this guy handles many vettes every year, he must be somewhat familiar with them.
MFH
MFH
Le Mans Master
Joined: Jun 2004
Posts: 6,269
Likes: 50
From: Dallas Texas
St. Jude Donor '06-'07-'09-'10
Originally Posted by mfh4
I was told by one of the largest Corvette dealers in Michigan that this tapping noise is coming from the fuel injection system and is common in the C5's. Since this guy handles many vettes every year, he must be somewhat familiar with them.
MFH
MFH
It's common alright, but your dealer is giving you a spin job regarding the FI system.
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Tech Contributor
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St. Jude Donor '05-'06-'07-'10
Originally Posted by 16Again
Piston slap and it's fairly common. No problem (so GM says) 
Bob
Bob
Oh yeah my '97 has the slap. It just doesn't sound right but taken from Patches quote, it's a "pleasability issue, not durability". My car has had it in the two+ years that I've owned her and it hasn't changed at all, no worse, no better. Once I learned about the real cause I stopped worrying about it.Paul
p.s. Fantastic post Patches
Race Director
Joined: Oct 2002
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From: Vancouver
2015 C5 of Year Finalist
St. Jude Donor '05-'06-'07-'08-'09-'10
I also get a ticking sound but if I push the clutch in it disappears. This is also a normal sound. If the car is on a slant when stopped it happens more often. My .02
Melting Slicks
Joined: May 2003
Posts: 3,174
Likes: 0
From: arlington tx
my parents old 2000 chrysler 300M did it and my grannies 2000 chrysler concorde does it also. many cars do it and they say no problemo. mine doesnt do it that ive noticed but then again what noise can u hear when the slp's wake up?
Melting Slicks
Joined: Nov 2003
Posts: 2,947
Likes: 2
From: Atlanta GA
i noticed this "ticking" this morning, it was pretty loud and noticible. I was like man... i really hope i dont need to blow the bank on fixing something internal on the engine... after reading this thread im feel much more relieved 
man i love this place!
man i love this place!
Racer
Joined: May 2000
Posts: 363
Likes: 0
From: Eureka CA
This is soooo frustrating!
When I bought my 97 used in 2002 I did not hear the "ticking" noise. Upon returning from the National Corvette Caravan to Bowling Green, KY on cold start-ups it developed the "ticking or slapping" noise until it warmed up!
Needless to say, I was very disappointed.
I was faced with this "ticking/slapping" noise on every cold start-up for about 10 months then it went away!!!!!!!
Go figure. I didn't do anything to "fix" it. I did buy a can of GM Top End Cleaner, but never used it. Oil was changed on schedule.
So what caused the noise to appear then disappear???????
When I bought my 97 used in 2002 I did not hear the "ticking" noise. Upon returning from the National Corvette Caravan to Bowling Green, KY on cold start-ups it developed the "ticking or slapping" noise until it warmed up!
Needless to say, I was very disappointed.
I was faced with this "ticking/slapping" noise on every cold start-up for about 10 months then it went away!!!!!!!
Go figure. I didn't do anything to "fix" it. I did buy a can of GM Top End Cleaner, but never used it. Oil was changed on schedule.
So what caused the noise to appear then disappear???????
