Have a rattle in the vehicle (91 Chev K1500, 4.3 V6). Sounds like it is coming from the engine, but not certain.
What does piston slap sound like?
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Piston slaps bear a strong resemblance to rod knock noises.
There are several videos of this on different cars, assuming there are car-specific versions. In this video shared, the very first comment tells the poster that the noise he or she is hearing is not piston slap, rather rod knock.
Quote:
Its a rod knock. Piston slap is audible during acceleration from a cold start that lasts for about 5 to 8 minutes of driving.
Rod knock is a hollow, metallic tapping noise that sounds like a cross between shaking a can of spray paint and tapping on a cylinder with a hammer.
Not to be a Debbie Downer to you, but, is there any way you can show us a video or hear some kind of audio of this noise? Is the engine moving during the rattle? Many things could be going on.
Also.
There are several videos of this on different cars, assuming there are car-specific versions. In this video shared, the very first comment tells the poster that the noise he or she is hearing is not piston slap, rather rod knock.
Quote:
Its a rod knock. Piston slap is audible during acceleration from a cold start that lasts for about 5 to 8 minutes of driving.
Rod knock is a hollow, metallic tapping noise that sounds like a cross between shaking a can of spray paint and tapping on a cylinder with a hammer.
Not to be a Debbie Downer to you, but, is there any way you can show us a video or hear some kind of audio of this noise? Is the engine moving during the rattle? Many things could be going on.
Also.
Before I started working on my first turbo system for my Fiat Spider back in 1998, in preparation, I installed this high dollar knock-retard system called a J&S Safeguard. The owner told me he actually designed this system for a Fiat 131 which uses the exact same engine as my Spider.
Before I even installed the turbo, the system said the knock sensor was picking up engine knock. I couldn't hear any detonation or any other unusual noises otherwise. The odd thing was I filled up with Sunoco's racing fuel just to see if this had any effect and it actually seemed to effect it in a positive way.
I tried moving the knock sensor to different locations on the engine but eventually gave up on the system, sold it on Ebay and went with a Jacobbs Boostmaster which allowed an automatic of retard under boost and now I run a simple 5 pin GM HEI control module with a fixed 5 degree retard when the turbo spools up.
I had posted this on one of the Fiat forums and the designer was doing a Google search to see what people were saying about his product when he saw my post and emailed me to tell me why he said it didn't work on my car. He said the knock sensor (made by GM) was prone to confusing engine knock with piston slap. He said in my case, the system would not work.
When I replaced a headgasket a few years ago I was cleaning some of the carbon buildup off the pistons and noticed at TDC, I could actually move the pistons by hand like the guy in the video was doing.
But the thing is, this has never caused me any problems. The reason for the headgasket replacement is Fiat twin cams are prone to leaking on the exhaust side below the distributor as well as the gasket between the exhaust cambox and head gasket in that same location. The head gaskets usually blow at 60K miles anyway so adding a turbo probably shortened it a bit. So I wanted to catch it before it actually blew.
Otherwise this is the same engine I had rebuilt back in 1992. I have no idea how many miles is on this block.
Every now and then when it's really cold outside, I will here what sounds like piston slap on my Subaru then it goes away when the engine heats up. I understand Boxer engines are supposedly more susceptible to this for some reason. Otherwise in the summer, my Subaru does not generate any piston slap. Just at subfreezing temperatures.
Before I even installed the turbo, the system said the knock sensor was picking up engine knock. I couldn't hear any detonation or any other unusual noises otherwise. The odd thing was I filled up with Sunoco's racing fuel just to see if this had any effect and it actually seemed to effect it in a positive way.
I tried moving the knock sensor to different locations on the engine but eventually gave up on the system, sold it on Ebay and went with a Jacobbs Boostmaster which allowed an automatic of retard under boost and now I run a simple 5 pin GM HEI control module with a fixed 5 degree retard when the turbo spools up.
I had posted this on one of the Fiat forums and the designer was doing a Google search to see what people were saying about his product when he saw my post and emailed me to tell me why he said it didn't work on my car. He said the knock sensor (made by GM) was prone to confusing engine knock with piston slap. He said in my case, the system would not work.
When I replaced a headgasket a few years ago I was cleaning some of the carbon buildup off the pistons and noticed at TDC, I could actually move the pistons by hand like the guy in the video was doing.
But the thing is, this has never caused me any problems. The reason for the headgasket replacement is Fiat twin cams are prone to leaking on the exhaust side below the distributor as well as the gasket between the exhaust cambox and head gasket in that same location. The head gaskets usually blow at 60K miles anyway so adding a turbo probably shortened it a bit. So I wanted to catch it before it actually blew.
Otherwise this is the same engine I had rebuilt back in 1992. I have no idea how many miles is on this block.
Every now and then when it's really cold outside, I will here what sounds like piston slap on my Subaru then it goes away when the engine heats up. I understand Boxer engines are supposedly more susceptible to this for some reason. Otherwise in the summer, my Subaru does not generate any piston slap. Just at subfreezing temperatures.
I only heard piston slap one time...it was on a test drive of a 2000 Camaro SS at my local Chevy dealer. It slapped pretty good on cold startup. But after 2-3 minutes of idling it was gone. From what I've read that's pretty typical of of LS1 piston slap.
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Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
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Originally Posted By: aquariuscsm
Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
Yep. Every time I've heard it, it started quieting down almost immediately. Unless the cylinder bores are past service limits or something.
Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
Yep. Every time I've heard it, it started quieting down almost immediately. Unless the cylinder bores are past service limits or something.
Originally Posted By: KingCake
Originally Posted By: aquariuscsm
Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
Yep. Every time I've heard it, it started quieting down almost immediately. Unless the cylinder bores are past service limits or something.
Yes as soon as the pistons expand a bit.
Originally Posted By: aquariuscsm
Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
Yep. Every time I've heard it, it started quieting down almost immediately. Unless the cylinder bores are past service limits or something.
Yes as soon as the pistons expand a bit.
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I had two 3000GT's,a 96 and a 98. My 98 would always slap for maybe 2 seconds at every startup. It's like you could literally hear and feel the oil being pumped up and coating the cylinders,stopping the slap. It only did this on 10W30 synthetic. With 10W40-20W50 dino it never slapped. I'm guessing the 10W30 synth drained completely off and back into the pan,whereas the thicker dinos stayed up in the engine better? My 96 never slapped. I always used Syntec 10W30 and 10W40 in it.
My car has a bit of piston slap. It's kind a muted sound, a bit like a quiet rod knock. Only when the engine is cold and mostly under acceleration. The sound fades during the first mile or so of driving, and then disappears. As the pistons warm-up, the piston skirt expands, eliminating the cold clearance that causes the piston slap.
I have a 2004 LM4 version 5.3. It was a dead end variant made for two years only. Aluminum block with cast iron headers (dumb move for cost savings I assume). Cold piston slap is very pronounced but goes away within a couple of blocks. However, it can be heard more softly when warm and you're in the garage or near a wall probably contributed to by the aluminum bock. At least you always hope that's what it is. The only times I have been able to defeat it both cold and hot was to use a 0-40 with an HTHS of 4.0 or above. RL 0-40 in my case but others might be just as good. With it quieting down I was able to rule out an exhaust leak caused by the aluminum/cast iron interface (which is also a known issue with the LM4). I am now back to 5-40 Motul (HTHS 3.7) and the slap is back too. But Motul Xmax is about half the cost so ..... slap ain't so bad.
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Originally Posted By: CT8
Originally Posted By: KingCake
Originally Posted By: aquariuscsm
Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
Yep. Every time I've heard it, it started quieting down almost immediately. Unless the cylinder bores are past service limits or something.
Yes as soon as the pistons expand a bit.
That's been my experience as well.
Rod-knock is there all the time, hot or cold. Worst one I ever heard was on a V8 Thunderbird belonging to a neighbor's meathead kid. The noise could be heard across the street, a heavy, deep-sounding thud; sounded like a single bearing had gone bad.
Originally Posted By: KingCake
Originally Posted By: aquariuscsm
Piston slap I've heard only lasts for a few seconds upon first startup. 2-4 seconds max.
Yep. Every time I've heard it, it started quieting down almost immediately. Unless the cylinder bores are past service limits or something.
Yes as soon as the pistons expand a bit.
That's been my experience as well.
Rod-knock is there all the time, hot or cold. Worst one I ever heard was on a V8 Thunderbird belonging to a neighbor's meathead kid. The noise could be heard across the street, a heavy, deep-sounding thud; sounded like a single bearing had gone bad.
Originally Posted By: KingCake
that piston slap video you posted sounds more like rod knock to me...
x2 thats not slap thats knock LOL
My 2002 chevy had slap,250K miles and still runs
that piston slap video you posted sounds more like rod knock to me...
x2 thats not slap thats knock LOL
My 2002 chevy had slap,250K miles and still runs
Originally Posted By: otis24
Have a rattle in the vehicle (91 Chev K1500, 4.3 V6). Sounds like it is coming from the engine, but not certain.
Most of the time it sounds like a rattle in the engine when its cold but goes away within a few minute, it can however sound like a just like a rod knock especially on Subaru engines.
I looked at a ej22 that had a diagnosed light rod knock, it sure sounded like one even with the stethoscope, the problem was when it got really warm after 30 min or more it went away. I figured it cant be a rod and suggested running it to see if it got worse, its still exactly the same 50k miles later.
Have a rattle in the vehicle (91 Chev K1500, 4.3 V6). Sounds like it is coming from the engine, but not certain.
Most of the time it sounds like a rattle in the engine when its cold but goes away within a few minute, it can however sound like a just like a rod knock especially on Subaru engines.
I looked at a ej22 that had a diagnosed light rod knock, it sure sounded like one even with the stethoscope, the problem was when it got really warm after 30 min or more it went away. I figured it cant be a rod and suggested running it to see if it got worse, its still exactly the same 50k miles later.
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