Piston Slap
Instructor
Joined: Aug 2010
Posts: 124
Likes: 0
From: Bowling Green Kentucky
Piston slap sounds like rattling a coffee can full of marbles and is common on engines like ours that have a short-skirt piston design. This is a "typical" long-skirt piston:
And here is a short-skirt style piston:
Notice on the first piston that there is a long "skirt" extending well below the piston pin - unlike the second picture. The longer skirts produce more drag and friction in the engine, which is part of the reason they don't use them in our engines.
The "slap" is the sound of the piston skirts hitting the cylinders walls as thrust direction changes. You only hear it when the eninge is cold because the pistons heat up as the engine gets hot, the clearance betweem the pistons and the cylinder walls reduces and the sound becimes inaudible.
As many of these engines as we've seen go 250K miles and more, I doubt it's anything to worry about. It may sound disconcerting, but it's just the nature of the beast.
And here is a short-skirt style piston:
Notice on the first piston that there is a long "skirt" extending well below the piston pin - unlike the second picture. The longer skirts produce more drag and friction in the engine, which is part of the reason they don't use them in our engines.
The "slap" is the sound of the piston skirts hitting the cylinders walls as thrust direction changes. You only hear it when the eninge is cold because the pistons heat up as the engine gets hot, the clearance betweem the pistons and the cylinder walls reduces and the sound becimes inaudible.
As many of these engines as we've seen go 250K miles and more, I doubt it's anything to worry about. It may sound disconcerting, but it's just the nature of the beast.
Thanks for the explanation mcm95403! This slapping seems to me like it would either damage the cylinder walls leaving minor dings, or leave marks on the side skirts, is that idea flawed? Or are the metals so hardened due to the immense heating and cooling that the minor "slapping" that occurs is "childs play" so to speak, meaning that no damage is done internally.
Le Mans Master
Joined: Sep 2010
Posts: 5,520
Likes: 5
From: Long Island NY
Mine started at about 50K or so and I have been assured by more than one Chevy tech that this is normal and will have no effect on reliabilty or longevity. I find it worse during the colder months and almost a non issue during the warmer months. When it is present all I do is let the car idle for about 1-2 minutes before putting it into gear and the noise is gone. You can only hear it when you first start the car cold and just drive without letting it warm up a bit and even then the noise disappears after about driving for about 15-30 seconds. I now have 74K on the clock and the car runs great, THANK GOD!
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
Thanks for the explanation mcm95403! This slapping seems to me like it would either damage the cylinder walls leaving minor dings, or leave marks on the side skirts, is that idea flawed? Or are the metals so hardened due to the immense heating and cooling that the minor "slapping" that occurs is "childs play" so to speak, meaning that no damage is done internally.
Race Director
Joined: Aug 1999
Posts: 11,119
Likes: 672
From: SE Pennsylvania
St. Jude Donor '03 thru '26
Oldtimer
% of LSX engine with piston slap ?
FWIW: at the Porsche-forum. they have piston slap in their engines as well ! Misery loves company.
Burning Brakes
Joined: Aug 2002
Posts: 1,090
Likes: 8
From: Indianapolis Indiana
I have 3 C5s, a 2000 A4, a 2001 A4 and a 2001 MN-6. All 3 slap when cold. Its annoying but I try to ignore it. I trust the guys on here are right that its not something to get concerned about.
